Showing papers in "Journal of Morphology in 1977"

A scanning electron microscopic study of the sacculus and lagena in the ears of fifteen species of teleost fishes

Abstract: The ulstrastructure of the saccular and lagenar maculae were studied in 15 species of teleost fishes, using the scanning electron microscope. Particular attention was paid to hair cell orientation patterns, composition of the ciliary bundles on the hair cells, hair cell distributions, and supporting cell types. The hair cells on both otolithic organs are divided into several groups with all of the hair cells in each group oriented in the same direction. The posterior region of the saccular macula in all species had dorsally oriented hair cells on the dorsal half of the macula and ventrally oriented hair cells on the ventral half. The cells on the anterior end of the macula were oriented anteriorly and posteriorly, with the posterior group, in most species, being on the dorsal half of the anterior region of the macula. There was considerable inter-specific variation upon this basic pattern. Inter-specific variation on the lagenar macula was considerably less than on the saccular macula. The basic pattern in all of the species includes one dorsal cell group and one ventral cell group. There are four more-or-less discrete ciliary bundles, each varying in the relative size of the kinocilia and stereocilia. Intermediary forms were also observed, making it difficult to differentiate ciliary bundles in some instances. It was apparent, however, that several of the ciliary bundles were found in particular macular regions.

Tongue evolution in the lungless salamanders, family Plethodontidae. II. Function and evolutionary diversity.

Abstract: A recently presented model of tongue projection dynamics is used to generate a series of predictions concerning morphologies to be expected under selection for increased distance of projection, increased speed of projection, and increased directional versatility. A general understanding of biomechanical events and the model are used as points of departure for making specific predictions concerning details of structure in skeletal, muscular and connective tissue components of the tongue and associated structures. Comparative methods are used to examine these predictions in the genera of plethodontid salamanders. These salamanders are known to project their tongues to different degrees, and this knowledge is used to test the hypotheses concerning morphological specialization. Three distinct groups of plethodontid salamanders have evolved specializations for long distance projection, and these genera differ from one another in important ways in respect to specific character complexes. For example, the tropical genera and Hydromantes use CBII as the major force transmission element in the skeleton, while Eurycea and its allies use CBI in this role. Hydromantes differs from both in having a uniquely proportioned and structured hyobranchial skeleton and associated musculature. Less extreme specializations for tongue projection are found in different combinations in three other groups. Finally, two distinct groups of generalized species having only limited tongue projection capabilities are recognized, each having a unique complex of inter-related features. Each of these eight groups is recognized and characterized as a functional mode, and hypotheses concerning the biomechanical meaning of the character complexes of each are formulated.

Ultrastructural study of the normal degeneration of the intersegmental muscles of Anthereae polyphemus and Manduca sexta (Insecta, Lepidoptera) with particular reference of cellular autophagy.

Abstract: In studying ultrastructural changes in metamorphosis-related degeneration of intersegmental muscles in Antheraea polyphemus, particular attention was directed to the mechanisms and timing of degradation of organelles and myofilaments. At emergence, the muscles are typical slowly contracting insect muscles, with a few dense body lysosomes and occasional autophagic vacuoles containing mitochondria. During the early phases of degradation the number of autophagic vacuoles, dense bodies, and lamellar bodies increases rapidly, along with an expansion of the Golgi system and the T system. Free glycogen particles and glycogenosomes are demonstrated by the PATAg test. Between 7 and 20 hours after ecdysis the T system continues to expand, the fibers subdivide, and the contractile system is degraded. Myofibrils fragment; myofilaments are not enclosed in isolating membranes at the time of their dissolution. The destruction of individual filaments occurs rapidly, with few intermediate stages being seen, while thick filaments tend to disappear earlier than thin filaments and Z-line material. The process is generalized and not confined to specific regions of the fiber. Autophagy destroys cell organelles in apparent synchrony with the first signs of nuclear pycnosis. By 20 to 30 hours after emergence, the fibers are reduced to lamellae of polynucleate sarcoplasm containing no organized contractile material. The sarcoplasm is filled with autophagic vacuoles containing mitochondria, dense lamellar or residual bodies, and ribosome-rich sarcoplasm. The number of mitochondria is drastically reduced at this time. In the final phases of involution (40–49 hours after emergence) shedding of the residual sarcoplasm precedes the expulsion of the pycnotic nuclei into the hemocoele. These results indicate that autophagy is responsible for the selective destruction of mitochondria, glycogen particles, ribosomes, and other organized sarcoplasmic structures. The one exception is the dissolution of the myofilaments, a process which remains undefined but which appears to be independent of lysosomal activity.

Morphology of the macula neglecta in sharks of the genus Carcharhinus

Abstract: Ears from several species of carcharhinid sharks were studied by gross dissection, light microscopy, transmission electron microscopy, and scanning electron microscopy. Structures along a possible sound transmission path to the ear are described, but main consideration is given to the structure of the macula neglecta. The macula neglecta is composed of two patches of sensory epithelium which line part of the posterior canal duct. In an adult shark the larger of these contains 224,000 sensory hair cells oriented so as to detect forces directed posteroventrolaterally in the duct. The smaller patch contains 43,000 hair cells oriented so as to detect oppositely directed forces. These receptor cells project through numerous small terminals to a total for both patches of 4,700 myelinated nerve fibers. Cytostructural variations throughout the hair cell population are also reported. Estimated acoustic properties of the tissues in this complex and the processing potential of the neural elements are interpreted as suggestive of auditory function. A mechanism based on the geometry of the receptor arrays is proposed to explain behaviorally observed instantaneous sound localization from the farfield. Evolution of the macula neglecta is reviewed, and evidence for homology of the macula neglecta and amphibian papilla is presented.

Development of dorsoventral polarity and mesentoblast determination in Patella vulgata

Abstract: In Patella vulgata the 32-cell stage represents a pause in the mitotic activity prior to the differentiation of the mesentoblasts mother cell 3D. At the onset of this stage, the embryo is radially symmetrical. Nevertheless, the plane of bilateral symmetry is indicated as it passes through the macromeres forming the vegetal cross-furrow. From the early beginning of the 32-cell stage, all four macromeres introdude far into the interior and tough the centrally radiating cells of the first quartet of micromeres. The two cross-furrow forming macromeres (3B and 3D) intrude the farthest and come into contact with the greatest number of micromeres. Finally, the contacts are extended significantly and maintained with only one of these macromeres. From that moment, this cell can be called the macromere 3D and the dorsoventral axis is determined. The evolution of the internal cell contacts between the micromeres of the first quartet and the macromeres indicates an essential role of the former in the determination of one of the latter as the masentoblasts mother cell, and thus in the determination of dorsoventral polarity.

The osteology and musculature of the pectoral limb of small captorhinids.

Abstract: The osteology of the pectoral limb of small captorhinids is described and figured in detail. A cartilaginous sternum was present. The glenoid was not a simple sliding or rocking joint, as was previously supposed, but considerable rotation was also an integral part of the humeral movement. The structure of the elbow joint is such that when the lower arm was extended, its distal end swung forward and extended the anterior reach of the hand. When the lower arm was flexed, the posterior reach of the hand was extended. Articulated specimens allow a recontruction of the manus. There was no well developed wrist joint, but rather the manus, as a whole, was a flexible structure. A pisiform was present. Sesamoid bones were developed in the tendons of the palmaris communis profundus muscle. Study of forelimb musculature of living reptiles based on dissections and the literature indicates that its evolution has been very conservative. The forelimb musculature of small captorhinids probably was very similar to that of all living reptiles except turtles.

The coelomocytes of the earthworm Lumbricus terrestris: morphology and phagocytic properties

Abstract: The coelomocytes of Lumbricus terrestris have been classified and described, based on Wright's stained preparations and on living cells. The five major categories consist of basophils, acidophils, neutrophils, granulocytes and chloragogen cells. Both the acidophil and chloragogen cell groups contain two subgroups. Granulocytes also exhibit heterogeneity with respect to staining properties of granules. Some possess acidophilic granules, some basophilic granules, and others contain both types. Granules of acidophils have been observed to be occasionally excreted from the cells. All cell types, with the exception of chloragogen cells, produce pseudopodia and are capable of phagocytosis, a vital component of the earthworm's immune response.

Feeding in golden hamsters, Mesocricetus auratus.

Abstract: Simultaneous cine and electromyographic records of freely feeding, unanesthetized golden hamsters show that their motion and muscular activity during mastication differ from those of albino rats (Weijs, '75). Rats show only propalinal motion while hamsters show lateral translation as well. The masticatory muscles of hamsters and rats are generally similar, but their molar dentitions differ. The interlocking molar cusps of hamsters restrict propalinal protrusion and retrusion when the molars are in occlusion; however, hamsters readily unlock occlusion by a twisting movement in the horizontal plane. Rats may perform propalinal movements even with the teeth in occlusion. In mastication the hamstery's jaw moves laterally as well as vertically and anteroposteriorly. Chewing orbits typically reverse after one to three orbits. Reversal begins at the start of the upstroke and involves a lateral shift in the opposite direction with the mouth closed. Electromyograms show that symmetric and asymmetric activities of closing protrusive and closing retrusive muscles produce a unilateral force couple on both sides. (This couple accompanies a midline closing stroke.) When the mouth is closed, unilateral activity of closing retrusors and closing protrusors also induces lateral translation. A bilateral force couple pits the retrusors of one side against the protrusors on the opposite side. Simultaneous with lateral excursion to the opposite side of midline and the action of these closing muscles, the anterior digastric and lateral pterygoid muscles of one side fire asymmetrically. The mandible moves downward coincidently with bilateral activity of the digastrics and lateral pterygoids. As the jaw opens further, activity differences of the lateral pterygoids accompany a shift of the mandible toward midline. At the end of the downstroke, all masticatory muscles studied are silent. The jaw returns to midline when the adductors fire asymmetrically at the start of closing. Trituration appears to coincide with an initial simple protrusion, which is subsequently accompanied by lateral translation. Different food types are reduced by distint chewing patterns with the differences clearest when the teeth are near occlusion. During gnawing the lateral pterygoids and digastrics fire longer, and the closing muscles fire less strongly. Chewing patterns in golden hamsters appear more generalized than those of rats; the differences may be directly associated with the ability of hamsters to store food in their cheek pouches.

Semicircular duct and ampulla dimensions in cat, guinea pig and man.

Abstract: Predictions from the classic theory of semicircular canal operation, the torsion pendulum model, depend upon labyrinthine dimensions and the physical properties of the endolymph. The dimensions of the semicircular canal, duct and ampulla in cat, guinea pig and man were determined from measurements of magnified sections of decalcified temporal bones. Estimates of the effect of shrinkage were obtained from measures in fresh material and it appears shrinkage is probably only a fairly small factor. The dimensions so obtained were used to provide new estimates of the short time constant and other mechanical parameters of the torsion pendulum model in the three species.

Comparative study of the stomatogastric system of several decapod crustacea. I. Skeleton.

Abstract: The skeletal structure of the stomachs of several decapod Crustacea is described in detail. The general organization of the ossicles is similar for all species and the homologies of the elements can be recognized despite large variations from group to group. The Reptantia are characterized by a complex ossicle organization while the Natantia, on the other hand, are characterized by a simple organization. The various types of ossicle organization found in the decapod stomach can be arranged in a series ranging from simple to complex. The Brachyura have the most complex ossicle system and the Penaeidea the most simplified. This graded series of complexity closely follows the evolution of the Decapoda.

Efferent connections of the striatum in Tupinambis nigropunctatus.

Abstract: The striatum of the lizard Tupinambis nigropunctatus lies in the lateral wall of the telencephalon and consists of two major subdivisions: the dorsal striatum and the ventral striatum. Electrolytic lesions were placed in all parts of the striatal complex and in adjacent areas and the subsequent anterograde degeneration was studied using the Nauta-Gygax and Fink-Heimer techniques. Lesions in the dorsal striatum cause terminal degeneration in the ventral striatum both ipsi- and contralaterally. In addition, projections have been found to the lateral amygdaloid nucleus and to parts of the dorsal striatum not affected by the lesion. Following lesions in the ventral striatum fiber degeneration could always be observed in the ventral peduncle of the lateral forebrain bundle. Corresponding terminal degeneration was found in the anterior and posterior entopeduncular nuclei, the tegmentum mesencephali, the substantia nigra, the prerubral area, the mesencephalic central grey and the lateral cerebellar nucleus. When the large celled part of the ventral striatum was involved in the lesion additional degeneration could be traced to the nucleus rotundus via the dorsal peduncle of the lateral forebrain bundle.

The free swimming Pipa larvae, with a review of pipid larvae and pipid phylogeny (Anura: Pipidae).

Abstract: This paper describes the morphology of the free swimming Pipa larvae, compares them with Xenopus, Hymenochirus, and to some extent, Rhinophrynus larvae, and presents a morphological diagnosis of pipid larvae. Pipa and Xenopus have very similar chondrocrania. Hymenochirus is superficially different but has the same diagnostic features. The differences appear related to its small size and predatory habitus. Other aspects of anatomy, especially the filter apparatus are very different in each genus. The filter apparatus of Pipa is somewhat reduced and seems modified for the retention of relatively large (20+microns) particles. Similar adaptations may have been annectant to predations in Hymenochirus, which lacks a filter apparatus. However, varying states of seven character complexes, which cut across the varying ecology, show that there are two basic pipid lineages, each currently confined to Africa or South America, respectively. Recent finds of fossil South American Xenopus indicate that these two lineages separated before the continents did. This does not warrant the recognition of two subfamilies because Xenopus and Hymenochirus are too different. Pseudhymenochirus is not an intermediate between them; it is a primitive Hymenochirus. Eight character states separate pipid and rhynophrynid larvae.

The fibrocartilage skeleton and related structures of the ventral pouch of Balaenopterid whales

Abstract: The mandibular symphysis of rorqual whales, whales of the genera Megaptera and Balaenoptera, is characterized by a Y-shaped fibrocartilage structure that lies in the substance of the muscular ventral pouch of these animals. The stem of the structure joins with the symphysis and is usually indicated externally by an unfurrowed median strip of blubber that has been called the "cutwater" by earlier writers. The arms of the Y pass back and are superficially indicated in all rorqual whales as a ridge running parallel to the rami of the mandibles. This fibrocartilage skeleton of the pouch is most closely related to the mylohyoid muscle. The function of the fibrocartilage Y is probably linked with the jaw mechanics of these whales, but its precise function is otherwise not known.

Semicircular canal radii of curvature (R) in cat, guinea pig and man

Abstract: The radii of curvature (R) of the horizontal (Rh), anterior (Ra) and posterior (Rp) semicircular canals were measured by a new technique (called ROTA) for cat, guinea pig and man. For each canal, data points from the osseous canal were rotated and plotted by computer such that the plane of the sheet of computer plot corresponded to the plane best fitting that canal. The radius of each osseous canal was determined and where necessary, the radius of the arc of data points was corrected for thickness of the absent tissue. For cat, guinea pig and man there are differences in R between canals within a labyrinth suggesting that if other things are equal there could be differences in the average mechanical sensitivity of the canals, which is consistent with physiological recordings from primary vestibular neurons in the cat. The Rs determined by ROTA are compared with Rs determined by conventional histological means.

Structure and carbohydrate histochemistry of the esophagus in ten teleostean species

Abstract: The histology and carbohydrate histochemistry of ten teleostean esophagi were compared. Structurally, the four layers of a typical vertebrate digestive tract were consistently present. The epithelium was always stratified and in all but one species (Ictalurus nebulosus) contained taste buds. Esophageal mucous cells were not the typical goblet cells seen in other vertebrates but appeared to be of six different types, pairs of which were associated with particular families. In esocids, poorly developed mucous acini and serous monogranular cells were present. In all species, the subepithelial connective tissue was not divided into definitive lamina propriae and submucosae due to the absence of muscularis mucosae. Variably present in this connective tissue region were argentophilic fibers and in esocids only, randomly dispersed striated muscle fibers. The arrangement of the muscularis was reverse to that of the general vertebrate plan. In mucous cells, three general types of epithelial mucosubstances were identified and in broad terms were recognized as sulfomucins, sialomucins and neutral mucosubstances. Morphological differences were accompanied by differences in carbohydrate localization, each esophageal epithelium containing at least two different mucosubstances. However, the mucosubstances identified in each mucous cell had a profile of characteristics different in some respects from any other. Thus teleostean esophagi appear to perform an integrated diversity of functions as reflected by their complex morphology and carbohydrate histochemistry.

Tergal modifications associated with abdominal glandular cells in the Blattaria.

Abstract: Tergal abdominal modifications of 30 species of Blattaria (Dictyoptera) were studied by means of histological scanning electron microscopy techniques. Despite marked anatomical diversity of the glands, only a few basic types of cells are present. Male tergal glands which are involved in sexual behavior generally have glandular cells filled with electron transparent vacuoles (type 3a) and those with dense myeloid secretion (type 3b); in addition some have large cells without ducts, not in contact with the cuticle and surrounded by other cells (type 2). External setae, usually associated with these structures, are mechano-receptors or mechano-chemoreceptors. Glands not involved in courtship (e.g., defensive glands) usually have large glandular cells with a ductule that reaches the end apparatus secreted by the glandular cell itself (Type 3) but lack types 2, 3a, and 3b. Species which do not have distinctive tergal modifications may have concentrations of microscopic pores or openings associated with glandular cells on certain segments. The chemistry of the secretions produced by tergal glands is unknown for most species. This paper emphasizes the need for behavioral and biochemical studies to elucidate the biological significance of cockroach tergal glands.

An electron microscopic study of early developmental stages, myogenesis, oogenesis and cnidogenesis in the anthomedusa, Podocoryne carnea M. Sars.

Abstract: This descriptive electron microscopic study of the blastogenetic medusa development of Podocoryne carnea focuses on the earliest stages of primordium formation, myogenesis, oogenesis and cnidogenesis. The events which take place at the cellular level prior to the formation of stage 1 (Frey, '68), which are characterized by ecto- and entodermal accumulations of undifferentiated I-cells and the beginning of transdifferentiation of epithelial cells, have been subdivided into four distinct stages (U1-U4). The genealogy of cells participating in medusa differentiation indicates that some cell types of the medusa are derived by transdifferentiation from the polyp's epithelial cells, while others originate by differentiation from I-cells. The myogenesis of the subumbrellar muscle cells resembles vertebrate myocardiac differentiation in many respects.

Comparative studies on the structure of reproductive organs of four botryllid ascidians.

Abstract: Reproductive organs of four botryllid ascidians, Botryllus primigenus, Botryllus schlosseri, Botrylloides violaceus and Botrylloides leachi, were studied histologically. In every species, the egg follicle consisting of an egg and its inner and outer follicles, is attached to the follicle stalk, the vesicle being composed of a flat epithelium, which in its turn is connected to the atrial epithelium or to the brood pouch specialized from it. In B. schlosseri, the egg is ovulated into the atrial cavity and remains there held by the brood cup, of which the inner epithelium is derived from the follicle stalk and the outer one from the atrial epithelium. In B. primigenus, the brood pouch develops as a diverticulum of the atrial cavity, around the entrance of which a fold differentiates from the atrial epithelium and closes the pouch during embryogenesis. In both species of Botrylloides, the brood pouch is formed by the outgrowth of the thickened atrial epithelium into the blood space, the entrance of which is closed during embryogenesis. The discarded outer follicle completely disintegrates soon after ovulation in B. schlosseri, but part of it remains throughout embryogenesis in the blood space in B. primigenus or projecting into the interior of the brood pouch in Botrylloides. In primigenus, the testis, when it accompanies the egg follicle, is placed at the bottom of the brood pouch and the sperm is shed through the pouch prior to ovulation. In B. schlosseri and the Botrylloides species, the testis is located independently from the egg follicle and the sperm matures after ovulation.

Synaptic organization of the nucleus rotundus in some teleosts

Abstract: Synaptic organization of the nucleus rotundus was studied with the electron microscope in three teleost species belonging to the same order In spite of the different histological organization (non-laminated, incompletely laminated, and laminated), the same kinds of axon terminals (S and F) are observed in all species A fibrous layer which is clearly formed only in the laminated nucleus is composed of F1 terminals and dendrites from a layer of small cells The same kind of synapses formed between F1 terminals and dendrites of small cells are also found among glomeruli in the non-laminated and incompletely laminated nuclei The main constituents of glomeruli are S and F2 terminals and dendrites of large cells in the non-laminated and incompletely laminated nuclei, and are S terminals and star-like structures which correspond to the tips of the dendrites of large cells in the laminated nucleus The star-like structure contains numerous mitochondria and clusters of small polymorphic vesicles Some of the vesicles aggregate at thickened cell membranes of the structure as in presynaptic dendrites

Ankle flexor muscles in the cat: length-active tension and muscle unit properties as related to locomotion.

Abstract: The mechanical properties of the whole muscle and fast-twitch muscle units of the cat hindlimb pretibial flexors have been explored and related to normal locomotion. Tibialis anterior (TA) is parallel-fibered and functionally crosses a single joint, the ankle, whereas extensor digitorum longus (EDL) is pinnate and spans the ankle, knee, metatarsophalangeal and interphalangeal joints. The active tetanic tension of TA remains near its peak value over a range of muscle lengths associated with normal ankle movement. In contrast, the length-tension curve of EDL is sharply peaked. However, normal corollary action of the knee, ankle and metatarsophalangeal joints during stepping minimizes EDL's excursion and maintains it at or near a length optimal for peak tension development. EDL is capable of producing synchronous but sterotyped digit and ankle movements while TA provides for independent ankle flexion at all relevant joint angles. The mechanical properties of 84 TA and 98 EDL fast-twitch muscle units were studied by measuring twitch contraction time (≤45 msec), peak tetanic tension, response to repetitive stimulation, and contractile fatigue resistance during electrical stimulation of single alpha axons, functionally isolated from ventral root filaments. These mechanical properties were essentially similar for both muscles with the exception of mean peak tetanic tension which was 30% lower for TA units (14 gm-wt) than for EDL units (20 gm-wt). A high proportion of units in both muscles demonstrated fatigue resistance which is reflective of the repetitive, phasic demand upon these muscles during locomotion.

Initiation of the actinotrichial development in the early fin bud of the fish, Salmo

Abstract: Ultrastructural analysis of initial development of actinotrichia, the skeleton anlage of the pelvic fin buds, was performed on the rainbow trout, Salmo gairdneri. It shows that the first actinotrichial rudiments appear in the subepidermal space of the pseudoapical cap. No mesenchymal cell bodies or their filopods are present. Hyaloplasmic protrusions of the basal epidermal cells are seen in the subepidermal space, limited by a dermoepidermal boundary reduced to a discontinuous thin adepidermal lamina without a collagenous layer. These morphological data suggest that the epidermal pseudoapical cap probably initiates the development of actinotrichia. Later, mesenchymal cells invade the subepidermal space and are probably involved in the further growth of actinotrichia.

Spermatozoa of Ciona intestinalis and analysis of ascidian fertilization

Abstract: The complex array of vestments which surrounds the ascidian oocyte indicates that spermatozoa of these urochordates may be highly modified to effect penetration through the egg-envelopes and to achieve successful fusion with the female gamete. Examination of the spermatozoa of Ciona intestinalis reveals, however, that they lack an acrosomal vesicle and do not possess detectable amounts of actin. Furthermore, the spermatozoa do not undergo observable morphological alterations when exposed to ammoniated seawater, a treatment known to produce aggregation and an acrosome reaction in other organisms. Ciona spermatozoa do contain significant quantities of proteases. It is hypothesized that the localization of these enzymes may be related to the ridge-like surface ornamentation which is observed as a component of the head region of Ciona spermatozoa.

Structural correlates of forelimb function in fur seals and sea lions.

Abstract: Dissections, manipulation of ligamentary preparations, analysis of limb proportions, and quantitative aspects of forelimb myology are used to correlate forelimb morphology in fur seals and sea lions (sub-family Otariinae) with previously published data as to their locomotor function (English, '76a). Comparisons to structure and function in generalized fissiped carnivores are then used to elucidate locomotor adaptations in fur seals and sea lions. Unique features of forelimb function during swimming in these pinnipeds include the amounts of abduction-adduction and rotary movements used. Modifications of the size, attachments and fasicle architecture of the muscles and the structure and range of possible movement of the joints suggest that in fur seals and sea lions these movements (1) take place about the glenohumeral (shoulder) joints, (2) that the movements are probably finely controlled, and (3) that they contribute to the generation of massive forward thrust via the cooperative activity of muscles capable of generating large amounts of force throughout the range of movement. Recovery movements occur through a similarly large range, and modifications of forelimb anatomy either to minimize or overcome water resistance are noted. The adaptive significance of these modifications is interpreted as allowing fur seals and sea lions to swim at speeds necessary to feed on the fast swimming prey presumably abundant in their adaptive zone.

Mechanics of the syrinx in Gallus gallus. II. Electromyographic studies of ad libitum vocalizations.

Abstract: Records of electrical activity in the tracheal muscles of domestic chickens were obtained for a variety of ad libitum vocalizations. Primary attention was given to an analysis of events during the most complex call, crowing. Three pairs of muscles, Mm. tracheohyoideus, tracheolateralis, and sternotrachealis, can affect the configuration of a chicken's syrinx. The firing patterns of the three muscle pairs are related to their different abilities to affect the tension of the syringeal membranes. The influence of M. tracheohyoideus is most indirect and imprecise, and its role the least clearly defined. It appears to adjust the position of the trachea so that the syrinx is isolated from unpredictable and/or undesirable consequences of nuchal position and tracheal elasticity, and also helps draw the glottis caudad, thereby deepening the pharyngeal chamber. The other two muscles interact to control the tension of the vocal membranes. M. sternotrachealis relaxes the membranes by drawing the drum of the trachea caudad, or, via the syringeal ligament, by rotating the pessulus cranioventrad, or both. M. tracheolateralis tenses the membranes and/or prevents caudal movement of the origin of M. sternotrachealis, a necessity if the syringeal ligament is to rotate the pessulus. Vocalization depends on both syringeal configuration and appropriate air flow. Hence, tracheal muscles, syrinx, air sacs, and ventilatory muscles cooperate to form a vocal system. Cooperation elicits a surprising degree of redundancy. At least one call, a high pitched wail, may be produced by two very different techniques.

Structure of the sinus hair follicle in the big-clawed shrew, Sorex unguiculatus

Abstract: The structural features of sinus hair follicles in Sorex unguiculatus were studied by macroscopic dissection, serial section light microscopy and electron microscopy. The shrew has about 540 sinus hairs regularly arranged on the snout. The maxillary nerves innervating them are extremely thick, while the optic nerves are very thin. Thus the follicle must be one of the most important sense organs in this animal. In the follicle the ring sinus is well-developed and the trabeculae of the cavernous sinus are reduced in number and thickness. The ring bulge is not a unified structure but a pair of bodies which consist of head, stalk and attachment plaque. It is characterized by the presence of numberous thick collagen fibrils (400 nm) and appears to be mechanically rigid. Lanceolate nerve terminals, free endings, Merkel cells with nerve terminals and unmyelinated fibers are observed, but encapsulated endings are lacking in and around the follicles. Straight lanceolate terminals on the posterior side of the follicle are thick and three-sided in cross section, while those on the anterior side are thin and two-sided. Free endings are located on the anterior side of the follicle. These and other findings are discussed on the basis of the assumption that the Sorex sinus hair follicle is more specialized as a vibrating system than in other mammals.

The cranial nerves of the colubrid snakes Elaphe and Thamnophis

Abstract: The cranial nerves of adult Elaphe obsoleta quadrivittata and late embryonic Thamnophis ordinoides, were studied, respectively, by dissection and by microscopic examination of serial sections. There are 11 cranial nerves in these snakes; the spinal accessory (XI) cannot be identified. In general, the nerves are similar to those of lizards. Certain nerves usually combine into a trunk: the oculomotor (III), trochlear (IV), ophthalmic division (V1) and abducens (VI), form the ocular trunk, whereas the glossopharyngeal (IX), vagus (X), and hypoglossal (XII), compose the craniocervical trunk. No terminal nerve is found. The first nerve exists as the independent vomeronasal and olfactory proper nerves. There is a large lagenar (auditory) part of the eighth nerve. The three main divisions of the trigeminal nerve (V) have the widest distribution in the head. In addition, there is a pterygoid division (V4) in snakes, innervating the muscles of the upper jaw series of bones. The V4 is best developed in snakes among all vertebrates. A chorda tympani of VII is present. The glossopharyngeal is a small nerve. The vagus comprises a large laryngeal branch and a larger visceral nerve to the trunk. The hypoglossal heavily innervates the tongue musculature. There are four cephalic parasympathetic ganglia: ciliary, preorbital, infraorbital, and inferior alveolar. Several of the ganglia may also include sympathetic cell bodies. The ciliary ganglion innervates intraocular smooth muscle, whereas the other ganglia supply the various cephalic glands. No distinct superior cervical sympathetic ganglion is recognized. Sympathetics distribute in the head through the craniocervical trunk and its communications with the facial and trigeminal nerves.

Studies on the gill ciliation of the American oyster Crassostrea virginica (Gmelin).

Abstract: Latero-frontal, para-latero-frontal, and frontal ciliary tracts on the gill filaments of Crassostrea virginica (Gmelin) were studied with light microscopy and scanning electron microscopy. Latero-frontal cirri are complex structures composed of varying numbers of paired cilia. The multiple pairs of cilia which constitute a single cirrus are closely appressed for a portion of their length; they then branch laterally from the central axis in a plume-like fashion. Latero-frontal cirri of adjacent gill filaments create a filtration sieve which should be capable of retaining particles smaller than 1 μm in diameter. Para-latero-frontal cilia are short, closely spaced cilia arranged as a staggered row along the frontal side of each tract of latero-frontal cirri. Latero-frontal cirri and para-latero-frontal cilia occur on ordinary, principal, and transitional gill filaments. Frontal ciliary tracts of ordinary filaments are divided into a central, ventrally directed coarse tract, flanked on either side by a dorsally directed fine ciliary tract. The coarse tract is covered by cirri which are comprised of five to eight cilia, while the fine frontal tracts are made up of individually functioning cilia. The frontal ciliary tracts of principal and transitional filaments bear only dorsally directed fine cilia. The unique direction of effective beat of the coarse frontal cirri of ordinary filaments, in combination with the action of fine frontal cilia and the strategic location of mucus producing cells, is used to describe a possible mechanism for the sorting of filtered particles.

The actions of three hamstring muscles of the cat: a mechanical analysis.

Abstract: An analysis of mechanical and architectural aspects of three hamstring muscles in the cat, semitendinosus (ST), semimembranosus anterior (SMa), and semimembranosus posterior (SMp), is presented based on whole muscle tetanic tension profiles. Length-active tension curves for each muscle were obtained by electrical stimulation of the whole muscle with a train of stimuli at 100 pulses per second (pps) for 600 milliseconds. Information from motion picture analysis (Goslow et al., '73) and electromyographic (EMG) activity (Engberg and Lundberg, '69) as seen during the step cycle is combined with analysis of joint torques to present a picture of the differential functions of the three muscles. The length-active tension characteristics of ST and SMa are such that they develop high amounts of tension throughout their physiological excursions. Maximal tension is produced over a much more limited range by SMp. A division of labor for the three muscles is proposed: the one-joint SMa is shown to be a primary hip extensor whose action facilitates smooth oscillation of the leg. Torque and electrical activity during the step cycle indicate the two-joint ST is a primary knee flexor. The more limited range of maximum torque and variable EMG pattern of the other two-joint muscle, SMp, relate to the fact that it has primary activity during high speed gaits when it may act to initiate spine flexion and assist in hip extension. Excursion and activity data have led to the conclusion that biarticular muscles (ST and SMp) may benefit from the combined action of two joints to maintain near maximal tension and torque during active phases of the step cycle. Thus, biarticular muscles may have evolved as much for the mechanical and physiological benefits they derive as for two-joint action itself.

Intrinsic organization of snake dorsomedial cortex: An electron microscopic and golgi study

Abstract: The intrinsic organization of medial cortex in snakes, primarily of the genera Natrix and Boa, was studied using Golgi and electron microscopic techniques. The area has three distinct layers, each containing a characteristic population of neurons. Stellate cells comprise a relatively small population of neurons with their somata and dendrites restricted to layer 1, the most superficial layer. Their axons course horizontally in layer 1. Candelabra cells form the largest population of neurons in medial cortex. Their somata lie densely packed in layer 2 and are joined by specialized junctions. Ascending dendrites extend from the somata into layer 1. They consist of spine-free proximal segments and spine bearing distal segments. Descending dendrites extend from the somata into the upper half of layer 3. The proximal segments bear few spines but branch into several tapered, distal segments which have a moderate covering of spines. One or two axons originate from the descending dendrites and descend through layer 3. The axons bear collaterals in the deep half of layer 3 and eventually bifurcate in the alveus. The medial branches run into the septum; the lateral branches course through other cortical areas. The axons bear frequent varicosities within medial cortex. Periventricular cells lie in the deep half of layer 3, either singly or in clusters. Their ascending dendrites extend radially into layer 1 where they branch into distal segments which resemble those of the candelabra cells. Their descending dendrites arborize horizontally in the alveus and bear a moderate covering of spines. Ependymal cells line the ventricular surface and send radial processes through the area's depth bearing lamellate processes.

Avian scale development. Absence of an “epidermal placode” in reticulate scale morphogenesis

Abstract: Timed-sequence studies have shown that reticulate scales on the ventral footpads of birds do not undergo "epidermal placode" formation during their morphogenesis, but arise as symmetrical evaluations similar to the scales of snakes and lizards. Unlike the scutellate scales on the dorsal surface of the foot, in which the formation of an "epidermal placode" and its subsequent morphogenesis result in disticnt outer and inner epidermal surfaces, the reticulate scales elaborate only one type of epidermal surface.