Showing papers in "Journal of Anatomy in 1983"

Muscle development in large and small pig fetuses.

Abstract: The largest and smallest littermates were chosen by weight from litters of 38 days' gestation to 1 day post partum. Complete frozen sections of the semitendinosus muscle were used to provide a qualitative and quantitative account of the development of the primary and secondary generations of muscle fibres. The results showed that the time of formation of primary and secondary fibres, and the numbers of primary fibres formed, were the same in both large and small littermates. The number of secondary fibres formed, however, was lower in the smaller fetuses and resulted in there being a 17% difference in total fibre number at birth. Primary fibres in small fetuses were smaller, due to the smaller central myofibril-free region. This small size may have restricted the available surface area for secondary fibre formation. Fibre hyperplasia was found to cease between 85 and 95 days' gestation, and so the fibre number difference is likely to be permanent.

Analysis of the dental morphology of Plio-pleistocene hominids. I. Mandibular molars: crown area measurements and morphological traits.

Abstract: This study has used accurate measurements of crown area and precise assessments of the morphological traits of mandibular molars in an attempt to define the metrical and morphological characteristics of early hominid taxa. A total of 196 Plio-Pleistocene hominid molars were either allocated to one of six informal taxonomic groups or considered as individual cases. Accurate measurements of crown base area made from occlusal photographs have enabled us to estimate the effects of interproximal wear on crown areas. The average correction factor over the three molar types is around 2-4% with a maximum of 6%. The patterns of distribution of extra cusps show interesting differences between taxa. None of the M-1S in the two groups of 'gracile' hominids from East and South Africa bears a C6, but it is common in the two 'robust' taxa. The distribution of a C7 is the reverse of this, it being rare in the robust' taxa, and more common in the 'gracile' groups. There is thus no simple relationship between cusp number and tooth size. Our observations on the protostylid suggest that though it is more common in the 'robust' australopithecines than the 'graciles', when it does occur it is more strongly expressed in the 'gracile' group. The combination of simple metrical data, and the assessment of morphological traits, can help in the classification of enigmatic or incomplete specimens. Some isolated teeth from the collection at Koobi Fora can confidently be assigned to Australopithecus boisei, and useful guides have been provided for taxonomic assessment of the skull KNM-ER 1805, and the mandibles KNM-ER 1506 and 1820.

Growth and development of muscle fibres in the rainbow trout (Salmo gairdneri).

Abstract: The growth of red and white muscle was investigated in the rainbow trout, using fish from 2.2 cm to 71 cm in length. In the white muscle, fibre hyperplasia, initially, accounted for all muscle growth but its relative contribution decreased as the contribution from fibre hypertrophy increased. At and above about 65 cm there was no hyperplasia, and this corresponded approximately to the stage when there were no more fibres in the smallest size class (less than 20 microns). The results for the red muscle are more variable and hence more difficult to assess. Although red fibre hyperplasia may continue throughout growth, at 34 cm there are no fibres in the smallest size class, which possibly indicates no new fibre formation beyond this stage.

Analysis of the dental morphology of Plio-Pleistocene hominids. II. Mandibular molars--study of cusp areas, fissure pattern and cross sectional shape of the crown

Abstract: Accurate measurements of the absolute and relative size of individual cusps, the arrangement of the primary fissure system and the shape of coronal cross sections of the tooth crown have been used to investigate the pattern of variation in Plio-Pleistocene hominid mandibular molar teeth. Teeth were either grouped into one of six taxonomic categories or considered as individual cases. Univariate analysis of relative cusp areas shows that the two taxonomic categories of 'robust' hominids from East and Southern Africa have relatively small mesial cusps, but a relatively large entoconid and hypoconulid and Principal Component plots of the data show that the 'robust' categories can be distinguished on the basis of relative cusp size. Other evidence suggests that these differences are not likely to be the result of allometric phenomena. Fissure pattern was analysed using the X/Y coordinates of defined reference points. Patterns were compared by Procrustes analysis and the relationships between teeth contained in the resulting similarity matrix were portrayed using Principal Coordinates plots and a nearest neighbours table. The positions of the posterior fovea and the mesial longitudinal fissure were important for distinguishing taxonomic categories. The shape of the coronal profiles proved difficult to quantify, but there were consistent and distinct differences between the South African 'robust' sample and teeth included within the East African Homo category. When these results are combined with those of a previous study of overall crown size and the distribution of extra cusps, they allow the affinities of isolated teeth or contentious specimens to be assessed. For example, our results show that KNM-ER 1506 and 1802 are more similar to the East African Homo group than any other category, and they indicate that though SK 1587 and 1588 are small teeth, they nonetheless are closest to the South African 'robust' category in terms of relative cusp size, fissure pattern and crown profile shape. The closest affinities of the Taung First mandibular molars are also with the South African 'robust' sample.

Pulse shape of magnetic fields influences chick embryogenesis.

Abstract: A total of 295 chick embryos was exposed during the first 48 hours of development to pulsed electromagnetic fields of 100 Hz and 0.4 to 104 microTeslas (micro T), and findings were compared with those in 364 control embryos. General morphology was analysed and supplemented by light microscopy studies. Exposure to electromagnetic fields with a pulse rise time of 100 microseconds produced teratogenic changes when intensities of 1.0 and 13.9 micro T were used but not with lower or higher intensities, demonstrating a 'window' effect and ruling out the possible influence of a rise in internal embryonic temperature. Exposure to an electromagnetic field of 1.0 micro T specifically altered organogenesis of the truncal nervous system and drastically reduced the alcian blue-stained components, whereas with an intensity of 13.9 micro T, there were abnormalities in the circulatory system and foregut, altering cell-to-cell contacts in the walls of developing vessels. When embryos were exposed to intensities of 0.4 and 1.0 micro T with 2.0 and 42 microseconds pulse rise times, teratogenic effects were greater and alterations involved all developing systems. The most powerful effects were obtained with 1.0 micro T and 42 microseconds rise time. The findings confirm the sensitivity of chick embryos to electromagnetic fields of extremely low frequency and intensity and indicate that pulse shape may be a decisive parameter determining strong, slight, or no modification of embryonic development. Mechanisms of action of electromagnetic fields are still unclear, but induced alterations in extracellular glycosaminoglycans could be a causal factor in the observed malformations.

Ultrastructure of normal and torn menisci of the human knee joint.

Abstract: Normal human menisci obtained at autopsy (seven cases) and the injured and uninjured portions of torn menisci obtained at surgery (nine cases) were studied with the electron microscope The surface of menisci is composed of collagen fibrils surmounted by an electron-dense surface coat Most of the cells in menisci are chondrocytes but a few fibroblasts and cells of an intermediate form difficult to classify as either fibroblasts or chondrocytes also occur Mast cells are found at the vascularised periphery of the meniscus Myofibroblasts were found in the injured portions of menisci in three out of the nine cases studied A territorial matrix containing fibrils and proteoglycan particles with associated filaments is seen around or adjacent to chondrocytes, but sometimes this matrix is sparse or absent The interterritorial or general matrix comprises collagen fibrils of widely varying diameters (25-180 nm) set in a sparse interfibrillary matrix containing proteoglycan particles A few mature elastic fibres and several small or immature elastic fibres and collections of electron-dense filaments are seen in the general matrix Also seen in this region are calcified bodies and matrical lipidic debris derived by the shedding of cell processes and in situ necrosis of cells Other features seen in the matrix of the injured portion of the meniscus include: (1) membrane-bound cystic structures; (2) parting and fraying of collagen fibrils; and (3) pools of proteoglycan particles

Histology and fine structure of the muscularis mucosae of the human urinary bladder.

Abstract: Study of biopsy specimens has revealed the presence of a muscularis mucosae in all regions of the human urinary bladder. The muscularis mucosae is discontinuous and consists of irregularly-arranged muscle bundles composed of relatively small-diameter smooth muscle cells. These cells are both morphologically and histochemically distinct from those forming the detrusor muscle, being rich in non-specific cholinesterase and glycogen. However, like detrusor muscle, the muscularis mucosae is richly supplied with acetylcholinesterase-positive nerve fibres. In the electron microscope, the constituent smooth muscle cells possess an extensive sarcoplasmic reticulum and large, peripheral clusters of dense glycogen granules; the myofilaments are confined to the central regions of the cells. Numerous intercellular junctions occur between adjacent cells while presumptive cholinergic nerve terminals containing small agranular and large granulated vesicles lie in close proximity to the muscle cells' surface.

Axon diameter and myelin sheath thickness in nerve fibres of the ventral spinal root of the seventh lumbar nerve of the adult and developing cat.

Abstract: The axon diameter (d) and the number of myelin sheath lamellae (nl) were estimated in electron micrographs of cross sectioned ventral spinal roots of the seventh lumbar nerve of adult cats, kittens and cat fetuses. Myelination started between the 40th and the 45th day after mating (about 3 weeks before birth). From birth onwards the calibre spectrum consisted of a group of small fibres and a group of large fibres. During the first two postnatal months the point distribution of the number of myelin lamellae plotted against the axon diameter appeared more or less linear. This point distribution pattern became curved from the 10th postnatal week onwards, and a function of the general expression: nl = C0 + C1d + C2 log(d) could be fitted to describe the regression. In adult cats, the mean number of myelin lamellae/axon diameter ratio was about 30 in the group of small and about 15 in the group of large fibres. Observations on immature animals indicated that the difference between the two fibre groups could have been established already during the third postnatal week. Considerable myelin production took place after the age of 1 year. The cross sectional area of the myelin sheath in the alpha fibre group increased about 10% after the age of 1 year, while in the gamma fibre group it increased as much as about 85%. The absolute amount of myelin per unit fibres. Differences and similarities between myelin production in the two fibre groups are discussed.

The re-innervation of olfactory glomeruli following transection of primary olfactory axons in the central or peripheral nervous system.

Abstract: The re-innervation of the olfactory bulb has been studied in rats in which the primary afferent axons were transected either in the peripheral nervous system, on the intracranial side of the cribriform plate, or in the central nervous system, in the nerve fibre layer of the bulb. Both procedures resulted in denervation of glomeruli on the dorsal surface of the olfactory bulb. Re-innervation of these glomeruli was first seen approximately three weeks after operation and was largely completed by the sixth week, irrespective of the site of the lesion. The similarity of the timing of re-innervation following the two procedures indicates that the cut fibres did not regenerate from their sites of transection. It is much more probable that the re-innervation axons were those of neurons newly generated in the olfactory epithelium. This view is supported by the results of other investigations, in which retrograde degeneration and subsequent replacement of the neurons have been found to follow transection of the olfactory nerves. After transection of the olfactory nerves, the new axons entering the bulb grew through the site of the lesion, across the interface between peripheral and central nervous tissue, through the nerve fibre layer and into the glomeruli. Thus, they followed the same course as normally growing primary olfactory axons. After the afferent fibres had been cut within the olfactory bulb, the site of transection was transformed into a scar composed largely of astrocytes. No olfactory axons grew through the scar and none passed beneath it in the deeper layers of the bulb. However, by tracing the anterograde axonal transport of horseradish peroxidase, it has been shown that axons immediately rostral to the lesion terminated in the re-innervated glomeruli. These denervated glomeruli were, therefore, probably re-innervated by axons that grew through the intact central nervous tissue of the nerve fibre layer on either side of the lesion.

The human vertebral column at the end of the embryonic period proper. 2. The occipitocervical region.

Abstract: The present investigation of the cervical region of the vertebral column at eight post-ovulatory weeks is the first such study based on precise reconstructions of staged embryos. At the end of the embryonic period proper, a typical vertebra is a U-shaped piece of cartilage characterized by spina bifida occulta. The notochord ascends through the centra and leaves the dens to enter the basal plate of the skull. The median column of the axis comprises three parts (designated X, Y, Z) which persist well into the fetal period. They are related to the first, second and third cervical nerves, respectively. Part X may project into the foramen magnum and form an occipito-axial joint. Part Z appears to be the centrum of the axis. The articular columns of the cervical vertebrae are twofold, as in the adult: an anterior (atlanto-occipital and atlanto-axial) and a posterior (from the lower aspect of the axis downwards). Alar and transverse ligaments are present. Cavitation is not found in the embryonic period in either the atlanto-occipital or zygapophysial joints, and is generally not present in the median atlanto-axial joint either. Most of the transverse processes exhibit anterior and posterior tubercles. An 'intertubercular lamella' may or may not be present, i.e. the foramina transversaria are being formed around the vertebral artery. The spinal ganglia are generally partly in the vertebral canal and partly on the neural arches, medial to the articular processes. During the fetal period, the articular processes shift to a coronal position and this alteration appears to be associated with a corresponding change in the location of the spinal ganglia.

A histological study of the innervation of developing mouse teeth.

Abstract: The innervation of developing mouse teeth between initial formation and crown formation was investigated using silver-stained serial sections. The developing innervation correlated with the stage of development of individual teeth rather than the chronological age of the mice. Nerves approached the developing dental papilla during the bud stage and formed a basal plexus below the dental papilla in the early cap stage. Nerve fibres from this plexus spread into the dental follicle as it began to develop. However, nerves did not enter the dental papilla until crown formation commenced, when the innervation was fairly rapid. Innervation commenced in the incisor teeth as soon as dentinogenesis started but not until a thin layer of enamel had been formed in the molar teeth. Although some of the early fibres were associated with blood vessels, many nerves lay free in the pulp. The absence of nerves in intimate relationship to the presumptive dental regions during the inductive phase of tooth development suggests that neural induction plays no part in the initiation of odontogenesis. However, it is not possible, from a purely histological study such as this, to attribute any function to the nerves at other stages of tooth development until the neurotransmitter content, and hence the type and likely function of the nerves, is established.

Receptors of the metacarpophalangeal joints: a histological study in the bonnet monkey and man.

Abstract: The histology of metacarpophalangeal joint receptors has been studied in bonnet monkeys (Macaca radiata) and in one human hand, using gold chloride and silver techniques. Paciniform corpuscles were the most numerous encapsulated receptors found; fewer Ruffini endings were present and these were exclusively in the palmar articular tissues. No Golgi endings were seen. It is suggested that these findings indicate a specialisation of the articular sensory apparatus towards detection of dynamic mechanical changes. Unencapsulated nerve endings were also found. Many of these were in close relation to blood vessels.

The role of movements in the development of sutural and diarthrodial joints tested by long-term paralysis of chick embryos.

Abstract: Chick embryos were paralysed in ovo with a neuromuscular blocking agent between 8 and 20 days of incubation. To evaluate the role of muscular activity in the development of sutural articulations, sutures of the cranial vault of control and paralysed embryos were studied histologically and the findings compared with the effect of the agent on the development of the ankle joint and some synovial joints of the jaws. Paralysed embryos showed a consistent lack of development of joint cavities in synovial joints. In most embryos, fusion of opposing cartilaginous elements had occurred. In contrast to synovial joints, sutural articulation showed a micromorphology comparable to that of controls. The findings indicate that different embryonic factors regulate the development of sutural and synovial articulations. Movements of neuromuscular origin play no essential role in the morphogenetic development of sutures, but are a prerequisite for the formation of joint cavities and other specialised structures of synovial joints.

Innervation of the gall bladder and biliary pathways in the guinea-pig.

Abstract: The innervation of the gall bladder and the biliary pathways was studied in guinea-pigs by means of histochemical methods for catecholamines and for acetylcholinesterase on whole mount preparations, on cryostat sections and on sections of plastic-embedded tissues. The gall bladder contains on average 367 neurons in a ganglionated plexus which lies at the outer surface of the muscle coat. The overall appearance of this plexus is rather similar to that of the submucosal plexus of the duodenum. From the gall bladder the plexus extends into the cystic duct, the hepatic duct and the common bile duct, but from the middle portion of the common bile duct downwards, it is positioned at or near the inner surface of the muscle coat. Concurrently with the marked increase in muscle thickness in the lower parts of the common bile duct, another ganglionated plexus appears, which is truly intramuscular. The latter plexus is highly developed, lies usually between longitudinal and circular muscle and resembles in appearance the myenteric plexus of the duodenum, with which it is in continuity. Throughout the biliary system, the extent of the ganglionated plexus is roughly related to the extent of the musculature. An exchange of adrenergic fibres between the ganglionated plexus and perivascular nerves is observed in the gall bladder. Another nerve plexus, without ganglia but rich in adrenergic and acetylcholinesterase-positive fibres, lies between the mucosa and the muscle coat. Very few nerve fibres run into the musculature of the gall bladder. On the other hand, in the thick musculature of the lower portion of the common bile duct, several intramuscular nerve fibres are found.

Osteoclasts and monocytes have similar cytoskeletal structures and adhesion property in vitro.

Abstract: The distribution of some cytoskeletal structures (microtubules, microfilaments, intermediate filaments) has been studied by indirect immunofluorescence microscopy and affinity purified antibodies in osteoclasts isolated from medullary bone of laying hens and in hen blood monocytes cultured in vitro. Both cell types show similar patterns of distribution of cytoskeletal structures and this further supports the concept that these cells are closely related. Osteoclasts and monocytes are also similar in their adhesion patterns, because they adhere to fibronectin-free areas and show closely comparable cell-to-substrate interactions when observed with interference reflection microscopy.

Ultrastructural changes in articular cartilage after experimental section of the anterior cruciate ligament of the dog knee.

Abstract: Ultrastructural changes in articular cartilage were studied in joint laxity induced by severing the anterior cruciate ligament of the right knee in sixteen mature dogs. The left knees provided controls; sham operations on six other dogs consisted of stab incision only, leaving the ligament intact. Cartilage from the medial tibial condyles was examined at intervals from two days to eighteen months later. In the superficial zone of the cartilage, collagen fibrils became abnormally widely spaced at four days, and narrower fibrils appeared from seven days after operation. Chondrocytes, particularly in the middle zone, became more active, with hypertrophy of cytoplasmic organelles detectable from four days. Superficial cells were initially healthy and became more numerous while their lipid content increased. The articular surface was fissured from two months and cell degeneration was rarely seen until several months after operation. These findings correlate with previous biochemical studies and are similar to early changes noted in degeneration of human articular cartilage.

Incidence of the metopic suture in adult Nigerian skulls.

Abstract: This study was carried out on 206 adult Nigerian skulls for the incidence of the metopic suture Metopism was present in 34% of cases, and a metopic suture (complete or incomplete) was observed in 3497% of the skulls The metopic suture was present in the lower part of the frontal bone, in various shapes, in 3010% of cases The most common shape observed was linear type (2427%) Inverted U-shaped, and wide side to side excursion, were found in 049% of cases of each kind, these being the least common form of the suture The incidence in the upper, upper middle and lower middle parts of the frontal bone was 049% in each type

Postnatal growth and differentiation of muscle fibres in the mouse. II. A histochemical and morphometrical investigation of dystrophic muscle.

Abstract: Postnatal development of three hind legs muscles, the soleus, plantaris, and gastrocnemius, of dystrophic mice (ReJ 129) was investigated with histochemical and morphometric methods. The results were compared with normal postnatal development. Especially during the second week postnatally, there was severe fibre necrosis with no apparent preference for any particular fibre type. This period of necrosis was shortly followed by a wave or regeneration during the third week that could not, however, compensate for the loss of fibres. In dystrophic animals of 4-5 months of age, the number of fibres was reduced by 40-70%. Cross sectional areas of dystrophic muscles rarely, if ever, exceeded values for normal animals 14 days of age, while body weights were also drastically reduced. Growth and differentiation of the nonaffected fibres proceeded almost normally during the first month. During the second month, the "slow' fibres in the soleus muscle, and the "fast-oxidative-glycolytic' fibres in the plantaris muscle were hypertrophied, while, incidentally, some "fast-glycolytic' fibres showed hypertrophy; but in this case the average size of the fibre type was not increased. After two months, a general fibre atrophy was observed. The fate of the regenerated fibres was difficult to trace, especially in muscles older than one month. It is assumed that a number of them were capable of developing into "adult' fibre types histochemically. During the course of the disease the percentage of "intermediate' fibres increased markedly, whereas nearly all "fast-glycolytic' fibres disappeared. Because of these shifts in fibre profiles, the plantaris and the gastrocnemius muscles obtained a rather "juvenile' and "oxidative' aspect. Changes in the histochemical character of the soleus muscle were less spectacular. In dystrophic muscles, no new fibre types were found, compared with normal muscles. Rather, fibre types were present at the wrong moment, or occurred in quantities unusual for the age concerned.

Age changes in the bone density and structure of the lumbar vertebral column.

Abstract: Old age is associated with a decline in bone density in lumbar vertebral bodies in both sexes, although the rate and amount of the decline is greatest in females. The bone translucency index method, described in this study, is a sensitive method of estimating bone density. The primary reason for this decline is the significant decrease in the number of transverse trabeculae of lumbar vertebrae in old age. It is postulated that the increase in vertebral end plate concavity and the increased horizontal dimensions of lumbar vertebral bodies in old age follows as a direct consequence of the selective loss of the transverse trabeculae.

Light microscopic, histochemical and ultrastructural studies of human lymph node paracortical venules.

Abstract: The light microscopic, histochemical and electron microscopic appearances of human lymph node paracortical high endothelial venules are described, and indicate that the vessels are metabolically active and involved in secretion. A comparison is drawn between these vessels and the majority of lymph node vessels lined by flat endothelium. The evidence suggests that these vessels are identical to similar vessels in the lymph nodes of experimental animals and which are known to be the site of selective migration of lymphocytes into lymph nodes. The correlation between the structural and cytochemical findings and their probable function is discussed.

The fine structure of autonomic neurons in the wall of the human urinary bladder.

Abstract: Using fresh biopsy specimens, intramural ganglia of the human urinary bladder have been examined by electron microscopy. The fine structural features of these neurons were compatible with their classification as parasympathetic in type. In several ganglia, groups of neurons were observed lying in close apposition to one another without any intervening satellite cell cytoplasm. Apart from occasional septate junctions the apposing membranes lacked any specialisation. The majority of terminals occurring in association with these intramural neurons were axosomatic in location. The terminals contained numerous small agranular and occasional large granulated vesicles and structurally were presumptive cholinergic in type. Occasional axon varicosities packed with a heterogeneous population of small agranular vesicles, large vesicles of variable density and multivesicular bodies lay in close association with the ganglion cells. The functional significance of these morphological features in terms of ganglionic transmission has been considered.

Fine structure of the canine tapetum lucidum

Abstract: The structure of the canine tapetum lucidum appears to be basically similar to that described in some other carnivores, but specific distinctions are present. The reflecting rodlets of the dog are similar in their dimensions to those of the cat, but they are more closely packed, resulting in a unique value for the wavelength of maximal reflectance. In addition, the rodlets are less precisely orientated, as compared to those of the cat, a condition which appears to result in a less efficient reflectance from the dog tapetum. It has also been shown that the dog does not possess a retinal tapetum lucidum, as had previously been suggested.

Three dimensional growth of the mouse isocortex.

Abstract: The three dimensional growth of the mouse isocortex was examined by plotting the variations in intermediate layer depth on orthogonal projections of the telencephalic surface at successive periods of development; a histological status was assigned to each depth. Thus portrayed, the development of the isocortex was seen as a propagated sequence of histological change, commencing at a rostral focus coextensive with the caudatopallial angle and thence spreading across the telencephalic wall. Growth was asymmetric about the focus of origin and terminated in a rostrocaudal direction as the spread of neuron production reached and extinguished a growth zone along the sagittal perimeter of the hemisphere. The possibility of mouse isocortical histogenesis representing a variation of a general mammalian pattern was noted, as was the evolutionary and methodological significance of the apparent coincidence of the origin of the gradient of isocortical neuron release with the region of cortex representing oropharyngeal structures. An alternative form of representation of the isocortical gradient, as the summation of a number of radial strips of tissue each with a similar history of neuron release and migration, was used to lay a foundation for a three dimensional model.

Localisation of motoneurons supplying the extra-ocular muscles of the rat using horseradish peroxidase and fluorescent double labelling.

Abstract: This paper describes a qualitative and quantitative investigation into the location of the motoneurons innervating the extra-ocular muscles of the rat. Injections of horseradish peroxidase, bisbenzimide, propidium iodide and DAPI-primuline were made either in one or simultaneously in two muscles. Unlike those of the cat, rabbit and monkey, the motoneurons which make up the oculomotor nucleus of the rat are not arranged in spatially separate subgroups belonging each to its corresponding extra-ocular muscle, but instead allow a high degree of superposition among the motor pools which they compose. The motoneurons innervating the lateral rectus and inferior oblique muscles are all homolateral; those of the medial and inferior rectus muscles are mainly homolateral with a few contralateral exceptions; and those of the superior rectus, levator palpebrae and superior oblique muscles are mainly contralateral with a small minority of homolateral exceptions. As well as from the main motor pools with which they are associated, the medial rectus, inferior rectus, superior rectus, levator palpebrae, superior oblique and lateral rectus muscles all receive innervation from motoneurons lying among the fibres of the fasciculus longitudinalis medialis. All these observations are supported by quantitative data.

Ultrastructure of the myocardium during development from early fetal life to adult life in sheep.

Abstract: The ultrastructure of the developing fetal lamb myocardium was studied in a series of animals spanning 29 days of gestation to term, and compared with newborn and adult animals. All major ultrastructural features which characterise the adult myocyte were found in early fetal life, although with considerably different degrees of development of specific features. Notably, myofibrils at 29 days of gestation are sparse and show little organisation. With advancing gestation there is an increasing number of myofibrils and the development of well defined striations. Thus, at term, the fetal tissue is not substantially different from the adult myofibril in the appearance of sarcomere structure. The observation of contractile tissue paucity and disorder in early fetal lamb myocardium is difficult to reconcile with available physiological data, which show an extraordinary pumping performance of the heart in vivo, and requires further investigation.

The Harderian gland, its secretory duct and porphyrin content in the mongolian gerbil (Meriones unguiculatus).

Abstract: The Harderian gland, its secretory duct and porphyrin content were examined in the mongolian gerbil (Meriones unguiculatus). The gland consisted of tubules lined by a single layer of epithelial cells and a myoepithelial network. The tubule cells were often binucleate and possessed lipid vacuoles in the apical half of the cell, a corona of granular endoplasmic reticulum surrounding the nucleus, and cytoplasmic 'slashes'. The latter are probably derived from dense membranous couplets and may be precursors of the lipid vacuoles. Holocrine and merocrine secretion was observed. Interstitial cells included plasma cells, mast cells and (predominantly) melanocytes which render the gland black. The gland was surrounded by a collagen capsule and an outer layer of highly attenuated (possibly endothelioid) cells. Within the gland, the secretory duct was lined by a single layer of normal tubule cells. Outside the gland, the duct enlarged to form an ampulla, from which clefts led off to deep crypts. The ampulla and clefts were lined by cells with small dense apical granules and stubby microvilli; some possessed lipid vacuoles. The crypts were lined by serous cells with active Golgi regions. At the duct opening, ampullary cells became squamous and goblet cells occurred. Geometric crystalloid deposits (with a layered structure of 7.6 nm periodicity) occurred at cleft-crypt junctions. Islets of extra-glandular ductal tissue were occasionally found within the gland. Porphyrins were detectable both by chemical assay and fluorescence microscopy. There was a trend for female glands to have a higher content than males. Solid intraluminal accretions of porphyrin and/or lipid were present.