The gross osseous anatomy of the spine has been the subject of much study but the internal architecture and trabecular anatomy of thoracolumbar vertebrate has not previously been well described. This study is based on high resolution x-ray images of 56 isolated thoracolumbar vertebrae and thick sections obtained from them. A previously undescribed array of trabeculae was documented which originated from the medial corner of the base of the pedicles and extended in a radial array throughout the vertebral body. This trabecular array persisted even in severely osteoporotic specimens. The cortex of the vertebral canal thinned abruptly near the base of the pedicle creating what may be a stress concentration at this site. This corresponded to the site of origin of the trabecular array. The presence of this possible stress concentration, in proximity to the trabecular array, may provide an explanation for the trapezoidal shape of the bony fragments that are frequently retropulsed into the spinal canal in axial load type burst fractures, common in this area of the spine.

Apoptotic cells of the human growth plate have not previously been demonstrated in situ. We have investigated the distribution of apoptotic cells in costosternal growth plates and bone of premature infants aged 4–11 d with a gestational age of ∼ 26 wk. In addition, we investigated the immunolocalisation of apoptosis-related proteins within the growth plates and associated bone. A proportion of late hypertrophic chondrocytes and osteocytes within newly formed primary spongiosa showed evidence of highly fragmented DNA. The incidence of osteocyte apoptosis decreased as the distance from the chondroosseous junction increased. Tissue transglutaminase (tTG) expression was associated with apoptosis of osteocytes and hypertrophic chondrocytes. In contrast the presence of tTG was demonstrated in osteoblasts and bone lining cells but it did not colocalise with evidence of apoptosis. The anti-apoptotic gene product Bcl-2 was absent from the growth plate but was present in osteocytes. Visual assessment indicated a greater occurrence of the protein in cells occupying regions of low apoptosis. P53 was not demonstrated in the growth plate or bone. These findings would indicate that human growth plate chondrocytes appear to show little provision for ensuring cell longevity. In contrast osteocyte apoptosis appears negatively correlated with the skeletal distribution of Bcl-2 protein in the human infant, implying a potential selective vulnerability in individual cells. Lack of Bcl-2 and the high incidence of osteocyte apoptosis in the more rapidly remodelling bone of the human infant suggest a potential role of osteocyte apoptosis in the remodelling process.

Knowledge of the structure and function of the central canal of the human spinal cord is important in understanding the pathogenesis of syringomyelia. Analysis of the morphology of the central canal is difficult using isolated histological sections. A 3-dimensional reconstruction technique using digitised histological sections was therefore developed to visualise the morphology of the central canal. The technique was used to study the canal in the conus medullaris and filum terminale of 1 sheep and 4 human spinal cords. A variety of morphological features were demonstrated including canal duplication, a terminal ventricle and openings from the canal lumen into the subarachnoid space. The findings suggest the possibility of a functionally important fluid communication in the caudal spinal cord which may have a sink function.

In the acinus of the sheep and mouse liver, lymphatic vessels are restricted to the portal tracts. Vessels less than about 25 μm across form a network around portal venules, and are closely associated with the limiting plate of hepatocytes. The perisinusoidal space of Disse is continuous with the interstitial space of the portal tracts at the origin of the sinusoids. It seems likely that excess interstitial fluid derived from the sinusoids flows along the perisinusoidal space of Disse to enter the portal tracts near the portal venules, and then enters the small lymphatics which lie adjacent to those venules. It then enters the larger vessels, which are adjacent to hepatic arterioles and bile ductules.

The shapes of cervical (C1–C7) and upper thoracic (T1, T2) vertebrae from the rat and the grey-headed flying fox have been analysed by Fourier analysis to investigate the types of variation present and to try to isolate bones according to position along the vertebral column and species. It was found that the T2 vertebrae of the rat are very different from all others in the study, that C2 and C6 vertebrae are very similar and that the remaining vertebrae split according to species.

The thermogenic potential of the interscapular brown fat pad in the naked mole-rat Heterocephalus glaber, that exhibits poikilothermic thermal responses to changing temperatures is reported. Histological and ultrastructural study of the brown fat pad showed that it consists of layers of skeletal muscle interposed between the layers of brown adipose tissue with both unilocular and multilocular adipocytes. Large numbers of mitochondria were present between and around the lipid droplets of these cells. Glyoxylic acid condensation, used to demonstrate catecholaminergic nerves, was evident in low concentrations in the connective tissue between the brown adipocytes. A 3-dimensional computer-aided reconstruction of the fat pad showed the extent and ramification of nerves and blood vessels between the adipocytes. These findings show that although the naked mole-rat is regarded as an endothermic poikilotherm, it possesses anatomical features usually found in homeothermic mammals, which are essential for thermogenesis.

The gross and microscopic anatomy of the Cape fur seal heart, lung, liver, spleen, stomach, intestine and kidneys (n = 31 seals) is described. Absolute and relative size of organs from 30 male seals are presented, with histological examination conducted on 7 animals. The relationship between log body weight, log organ weight and age was investigated using linear regression. Twenty five animals were of known age, while 6 were aged from counts of incremental lines observed in the dentine of tooth sections. For the range of ages represented in this study, body weight changes were accurately described by the exponential growth equation, weight = wort, with body weight increasing by 23% per annum until at least 9–10 y of age. Organ weight increased at a rate of between 25% and 33% per annum until at least 9–10 y of age, with the exception of the intestines, where exponential increase appeared to have ceased by about 7 y. The relationship between body weight and organ weight was investigated using logarithmic transformations of the allometric equation, y = axb, where the exponent b is 1 if organ weight is proportional to body weight. Most organs increased in proportion to the body. However, the heart, liver and spleen had exponents b > 1, suggesting that these organs increased at a faster rate than the body. The basic anatomical features of the viscera were similar to those of other pinnipeds, with some exceptions, including the arrangement of the multilobed lung and liver. Apart from the large liver and kidneys, relative size of the organs did not differ greatly from similar sized terrestrial carnivores. The histological features of the organs were generally consistent with those previously described for this species and other otariids. The heart, as in other pinnipeds, was unlike that of cetacea in not having unusually thick endocardium or prominent Purkinje cells. Notable histological features of the lungs included prominent fibrous septa, prominent smooth muscle bundles, cartilage extending to the level of the alveolar sacs and ample lymphoid tissue. The spleen had a thick capsule, well developed trabeculae and plentiful plasma cells. Abundant parietal cells were present in the fundic glands and lymphoid follicles were present in the gastric lamina propria, particularly in the pyloric region. Small intestinal villi were very long but this could have resulted from underlying chronic inflammation. Lymphoid follicles were prominent in the colon. The kidney reniculi each had a complete cortex, medulla and calyx, but a sportaperi medullaris musculosa was not identified.

The distribution of mu opioid receptors was studied in human fetal spinal cords between 12–13 and 24–25 wk gestational ages. Autoradiographic localisation using [3H] DAMGO revealed the presence of mu receptors in the dorsal horn at all age groups with a higher density in the superficial laminae (I–II). A biphasic expression was noted. Receptor density increased in the dorsal horn, including the superficial laminae, between 12–13 and 16–17 wk. This could be associated with a spurt in neurogenesis. The density increased again at 24–25 wk in laminae I–II which resembled the adult pattern of distribution. A dramatic proliferation of cells was noted from the region of the ventricular zone between 16–17 and 24–25 wk. These were considered to be glial cells from their histological features. Mu receptor expression was noted over a large area of the spinal cord including the lateral funiculus at 24–25 wk. This may be due to receptor expression by glial cells. The study presents evidence of mu receptor expression by both neurons and glia during early development of human spinal cord.

Collagen fibre organisation and fibril size were studied in the buccal gingival and hard palate mucosa of Macacus rhesus monkey. Light and electron microscopy analysis showed connective papillae exhibiting a similar inner structure in the different areas examined, but varying in distribution, shape and size. Moving from the deep to surface layers of the buccal gingival mucosa (free and attached portions), large collagen fibril bundles became smaller and progressively more wavy with decreasing collagen fibril diameter. This gradual diameter decrease did not occur in the hard palate mucosa (free portion, rugae and interrugal regions) where the fibril diameter remained constant. A link between collagen fibril diameter and mechanical function is discussed.

The aims of the present study were: (1) to supply further knowledge about variations in nonmetric cranial traits in relation to sex, age and laterality and (2) to evaluate biological distance between samples from a recent population. The incidence of 18 nonmetric variants of the cranium were determined in 3 adult samples of 394 skulls of known sex from North Sardinia (Sassari, Alghero and Ozieri); for the Sassari sample (n = 200) age at death was also known. Some significant sex differences were observed. Age did not appear to influence the frequency of the discontinuous traits but did for legibility. Side differences may provide important information about environmental influences. The interpopulation analysis indicates a stronger relationship between samples that are geographically closer (Sassari and Alghero), in accordance with other studies, strengthening the hypothesis of the validity of the use of nonmetric traits in the study of the peopling of a territory.

Careful histological observation of the development of the anlage of the inner ear in chicken embryos led us to question the traditional view of otic placode (OP) formation. First, morphological studies in the cephalic region carried out on stages preceding the appearance of the placodal epithelium revealed that the medial placodal cells are continuous temporally and spatially with cells belonging to the neural fold (NF). Second, both the formation of the basal lamina between the dorsal region of the neural tube (NT) and ectoderm and the pattern of formation of the neural crest present distinctive characteristics between otic levels and regions located anteriorly and posteriorly. Third, numerical comparisons of parameters for the NT and the OP between different levels of the rhombencephalon allowed us to assign a differential behaviour in the growth pattern of the otic region. These results indicated that the medial part of the OP is not derived from already independent ectoderm that increases in thickness under the influence of the NT (as previously accepted) but that it develops directly from the NFs. Although we do not exclude other possibilities, we propose that at least a proportion of the OP cells originate directly from cells committed to be neural crest. After this incorporation, basal laminal formation would delimit the NT from the OP without transition of the otic cells to ectoderm. This hypothesis would imply that part of the otic cells originate directly from neuroepithelial cells having a neuroectodermal (rather than the previously established ectodermal) origin.

A total of 50 permanent mandibular 1st molars of 26 children with Down's syndrome (DS) were examined from dental casts and 59 permanent mandibular 1st molars of normal children were examined from 33 individuals. The following measurements were performed on both right and left molars (teeth 46 and 36 respectively): (a) the intercusp distances (mb-db, mb-d, mb-dl, db-ml, db-d, db-dl, db-ml, d-dl, d-ml, dl-ml); (b) the db-mb-ml, mb-db-ml, mb-ml-db, d-mb-dl, mb-d-dl, mb-dl-d angles; (c) the area of the pentagon formed by connecting the cusp tips. All intercusp distances were significantly smaller in the DS group. Stepwise logistic regression, applied to all the intercusp distances, was used to design a multivariate probability model for DS and normals. A model based on 2 distances only, mb-dl and mb-db, proved sufficient to discriminate between the teeth of DS and the normal population. The model for tooth 36 for example was as follows:

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A similar model for tooth 46 was also created, as well as a model which incorporated both teeth. With respect to the angles, significant differences between DS and normals were found in 3 out of the 6 angles which were measured: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was higher, and the mb-dl-d angle was smaller. The dl cusp was located closer to the centre of the tooth. The change in size occurs at an early stage, while the change in shape occurs in a later stage of tooth formation in the DS population.

The proliferation sites and cellular kinetics of villous epithelial cells and M cells in the intestine of the adult chicken have never been clarified. In this study, we determined the proliferation sites in the chicken caecum using colchicine treatment and detection of proliferative cell nuclear antigen (PCNA). The cellular kinetics of these cells were also studied using bromodeoxyuridine (BrdU) as a tracer. Enterocytes in their mitotic period were observed along the entire length of the intestinal crypt of the caecum, with a denser distribution in the middle portion of the crypt, except for the caecal tonsil. The centres of distributions were at 49% of the distance from the bottom of the crypt in the base and 41% in the apex of the caecum. In the caecal tonsil, the centres of distributions were at 64% in the long type of crypt from the bottom of the crypt and at 44% in the short type of crypt. On the other hand, the PCNA-positive enterocytes were distributed more densely at the bottom of the crypt, except for the caecal tonsil. The centres of distributions were at 36% in the base from the bottom of the crypt, 37% in the body, and 34% in the apex. In the caecal tonsil, they were at 54% in the long type of crypt and 44% in the short type. The BrdU-labelled enterocytes reached to the basement of the intestinal villi in all caecal portions at 1 d after the BrdU administration. The leading edge of the labelled enterocytes disappeared from the villous tips at 4 d in the base and the body and 3 d in the apex. In the caecal tonsil, the BrdU-labelled microvillous epithelial cells and the M cells appeared near the orifice of the crypt at 1 d, and BrdU-labelled M cells were not observed in the crypt. Thereafter, almost all of these cells disappeared at 5 d from the follicle associated epithelium (FAE). These results suggest that M cells are transformed from their precursors within 1 d, and the turnover time for M cells occurs within 4 d after the cell division of the precursors.

Several studies have reported the morphological changes induced by unilateral enucleation during early neonatal life on the developing visual system. This study has examined cellular changes in the superior colliculi by removal of a single eye in adult rats. Anaesthetised male hooded rats aged 90 d had their right eyes removed. Groups of nonenucleated control and enucleated rats were killed when aged either 150 or 390 d. The brains were removed and both the right and left superior colliculi dissected out. The volume of the stratum griseum superficiale (SGS) within these colliculi was estimated stereologically by light microscopy, as well as the numerical density and total number of neurons within this cell layer. The volume of the cell layer was reduced by about 40% on the side contralateral to the enucleated eye but not on the ipsilateral side at both survival periods examined. The numerical density of neurons within the SGS was unaffected by the enucleation so that the colliculi contralateral to the enucleated eye showed a substantial loss of neurons within this cell layer. This study demonstrates the importance of the retinal ganglion cell input, even in adult animals, for maintaining the viability of neurons in the SGS layer of the superior colliculus.

Changes in the shape of erythrocytes circulating in large blood vessels of mice were examined by our ‘in vivo cryotechnique’. The abdominal aorta and inferior vena cava (IVC) were cut vertically with a precooled knife and simultaneously an isopentane–propane mixture (−193°C) was poured over them for freezing. They were freeze-substituted in acetone containing 2% osmium tetroxide. Some specimens were embedded in Quetol-812, and thick or ultrathin sections were examined by light or transmission electron microscopy. Serial ultrathin sections were used to reconstruct 3-dimensional images of native erythrocytes. Others were transferred into t-butyl alcohol and freeze-dried for scanning electron microscopy. The tissue surfaces were sufficiently frozen to prevent large ice crystal formation, and erythrocyte shapes were also preserved. The shapes of circulating erythrocytes appeared to be varied in the abdominal aorta but typical biconcave discoid shapes were rarely observed. Conversely, erythrocytes were approximately biconcave discoid in shape in the IVC. Our in vivo cryotechnique was useful for clarifying the in vivo morphology of erythrocytes circulating in large blood vessels.

We carried out a computerised tomographic (CT) examination to elucidate the modifications in the head related to orbital enlargement in the Baikal seal. Transverse CT images showed that (1) the external frontal contours and the frontal sinuses are compressed medially and ventrally by the orbital enlargement; (2) the caudal part of the nasal cavity and nasopharynx are compacted ventrally; and (3) the cranial cavity is displaced caudally. The neurocranium is obviously separated from the facial part in the transverse plane at the caudal region of the orbit. The disposition of the mandible, zygomatic arch, temporal bone, and the masseter, temporal, digastric and pterygoid muscles is changed by the enlarged orbit in the 3-dimensional reorganisation of the head in this species. It is suggested that adaptation for the Lake Baikal environment primarily resulted in orbital enlargement, and that the altered orbital design may subsequently have influenced the form and function of the masticatory and respiratory system.

The purpose of this investigation was to determine the amount of epineurium surrounding the recurrent laryngeal nerve (RLN) compared with a limb nerve, that to flexor hallicus longus (NFHL). Nerve samples were obtained from 10 adult dogs and studied using scanning electron microscopy and light microscopy to measure the relative proportion of epineurium and the relative proportions of adipose and collagenous tissue comprising the epineurium in both nerves. Significantly greater relative epineurial cross-sectional areas and adipose content were found in the RLN than in the NFHL. Based on observations on noncranial peripheral nerves, the findings indicate that the RLN is better protected against deformational forces associated with compression than stretching forces. The RLN may not be structured well for successful reinnervation after injury. The patterns observed for adipose tissue in RLN epineurial tissue appeared unique compared with those previously reported in peripheral nerves. The primary role associated with adipose tissue is to ‘package’ the nerve for protection. The RLN is considered to be a vital nerve in the body, as are other cranial nerves. The large proportions of adipose tissue in the epineurium may relate to the importance of protecting this nerve from injury.

Out of a total of 21 exencephalic p53-deficient embryonic and newborn mice, 6 (28.6%) possessed fused maxillary incisor teeth. On histological analysis of the 5 examples seen on day 19.5 of gestation and newborn mice, 3 varieties were observed: an example of ‘simple’ fusion, 3 examples of simple fusion each of which contained a ‘dens in dente’ (‘tooth within a tooth’), and a single example in which the fused teeth were associated with a median supernumerary incisor tooth which, while deeply indenting the labial surface of the fused teeth, was in all locations a completely separate unit. 3-D reconstructions of the fused teeth demonstrated that they were all of the fusio subtotalis variety. No gross abnormalities were observed in the other dentition in these mice. It is noted that in mice fused maxillary incisor teeth are relatively commonly associated with both hypervitaminosis A-induced and trypan blue-induced exencephaly. It is believed that the presence of dens in dente within fused maxillary incisor teeth has only once been reported in mice, and the association between fused maxillary incisor teeth and a median supernumerary incisor tooth has not previously been reported in this species.

The sternalis muscle is an uncommon anatomical variant. It is located on the human anterior pectoral wall, superficial to pectoralis major. This muscle has been reported both in males and females, and in whites, blacks and Asians (Barlow, 1934; Kida & Kudoh, 1991; Shen et al. 1992; Bradley et al. 1996).

Although the importance of this muscle is still a mystery, various different interpretations have been made. Clemente (1985) considered sternalis to be a misplaced pectoralis major, although some embryologists have viewed it as part of a ventral longitudinal column muscle layer arising at the ventral tip of the hypomeres (Sadler, 1995). Sadler claimed that this muscle is represented by rectus abdominis in the abdominal region and by the infrahyoid musculature in the cervical region; in the thorax, this layer usually disappears but occasionally remains as a sternalis muscle. Kitamura et al. (1985) reported a case of congenital partial deficiency of pectoralis major accompanied by an enormous sternalis. Barlow (1934), on the other hand, claimed that sternalis represents the remains of a panniculus carnosus.

A band of fascial thickening, termed the iliopubic tract, lies on the posterior aspect of the inguinal region and has been described in the surgical literature as playing an important role during herniorraphy. This study was undertaken to examine the gross and microscopic anatomy of the iliopubic tract in 12 cadavers. The results confirmed that the iliopubic tract can be readily identified as a thickening of the transversalis fascia running deep and parallel to the inguinal ligament. It attaches to the superomedial part of the pubic bone medially, but laterally its fibres fan out within the fascia transversalis and fascia iliaca without bony attachment to the iliac spines. In contrast to the inguinal ligament, the histological analysis of the iliopubic tract shows a high elastin to collagen ratio. The functional signficance of this structure merits further study, but there is no doubt that it is important in many approaches to inguinal herniorraphy. For this reason it is considered that the iliopubic tract deserves greater emphasis in the anatomy teaching of the inguinal region.