Search

Summary: The structure of the limbs of elephants is unusual among mammals. In African elephants (Loxodonta africana, Blumenbach 1797), the front limbs serve to support the greatest part of the body mass of the largest land animal. In this study, we present new and detailed anatomical data regarding muscular and specific fascial structures of the lower front limb which were examined by means of standard anatomical and histological techniques. The muscles and tendons of the forearm (antebrachium) and hand (manus) are tightly surrounded by thick, highly elastic fascial layers which fuse with the lacertus (lac.) fibrosus and the so‐called ligamentum (lig.) humeroulnare. A well‐developed musculus (m.) brachioradialis occupies the proximolateral aspect of the forearm and its tendon inserts together with the lac. fibrosus on the os carpi intermedium. The lac. fibrosus, the lig. humeroulnare and the m. flexor carpi radialis reveal a large proportion of elastic fibres. These three structures may play an important role in storing strain energy thus promoting energy‐saving locomotion. On the palmar aspect of the carpus, metacarpus and digits, short flexor, abductor, adductor, lumbricales and interossei muscles are present, whereas supinator muscles are absent in all specimens. The short muscles of the hand together with specific dorsal tendons enable precise movements of specific toes. [ABSTRACT FROM AUTHOR]

Although a number of brief, fragmented descriptions have been provided on the gross morphology of the ratite tongue, very few studies have documented the histological structure of this organ. This paper presents the first definitive histological description of the emu tongue and reviews, consolidates and compares the scattered information on the histology of the ratite tongue available in the literature. Five tongues were removed from heads obtained from birds at slaughter and fixed in 10 % neutral buffered formalin. Appropriate longitudinal and transverse segments were removed, routinely processed for light microscopy, and sections examined after staining with H & E and PAS. The entire tongue (body and root) is invested by a non-keratinized stratified squamous epithelium. The supporting connective tissue of the tongue dorsum displays only large, simple branched tubular mucus-secreting glands, whereas the caudal tongue body ventrum and tongue root, in addition to these glands, also exhibits small, simple tubular mucus-secreting glands. Herbst corpuscles are associated with the large, simple branched glands. Lymphoid tissue is restricted to the tongue ventrum and is particularly obvious at the junction of the ventral tongue body and frenulum where a large aggregation of diffuse lymphoid tissue, with nodular tissue proximally, was consistently observed. A structure resembling a taste bud was located in the epithelium on the caudal extremity of the tongue root of one bird. This is the first reported observation of taste buds in ratites. Forming the core of the tongue body is the cartilaginous paraglossum lying dorsal to the partially ossified rostral projection of the basihyale. The histological features of the emu tongue are generally similar to those described for the greater rhea and ostrich, except that taste buds were not identified in these species. The results would suggest that the emu tongue functions as a sensory organ, both for taste and touch (by virtue of taste receptors and Herbst corpuscles, respectively), as well as fulfilling an immunological function. [ABSTRACT FROM AUTHOR]

Despite numerous papers addressing the topic, the gross morphology of the ratite tongue and more specifically that of the emu, has been superficially or poorly described. This paper presents the first definitive macroscopic description of the emu tongue and reviews, consolidates and compares the scattered information on the gross morphology of the ratite tongue available in the literature. Twenty-three heads obtained from birds at slaughter were used for this study. Specimens were fixed in 10 % neutral buffered formalin, rinsed and the gross anatomy described. The emu tongue is divided into a body and a root. The body is triangular, dorsoventrally flattened, pigmented and displays caudally directed lingual papillae on both the lateral and caudal margins. The root, a more conspicuous structure in comparison to other ratites, is triangular, with a raised bulbous component folding over the rostral part of the laryngeal fissure. Following the general trend in ratites, the emu tongue is greatly reduced in comparison to the bill length and is specifically adapted for swallowing during the cranioinertial method of feeding employed by palaeognaths. This study revealed that it is not only the shape of the tongue that differs between ratites, as previously reported, but also its colour, appearance of its margins and root, and its length in comparison to the bill, and the shape of the paraglossum. [ABSTRACT FROM AUTHOR]

The article studies the macroscopic features of the venous drainage of the reproductive system of six pre-pubertal and three sexually mature and active ostrich. According to the authors, each testis was drained by one to four testicular veins, The right testicular veins drained the right testis and epididymis and its appendix to the caudal vena cava and to the right common iliac vein, whereas the left testicular veins drained the left testis and epididymis and its appendix exclusively to the left common iliac vein. The authors note the previous studies on the vascular system of the male reproductive tract in birds.

This study was performed to obtain information on yolk utilization in fasted and fed ostrich chicks posthatching. The fasted trial lasted for 7 d, whereas the fed trial continued for 16 d. Fasted ostrich chicks showed a decrease of 31.3 g of BW, with yolk weight decreasing by 28.9 g daily after hatching. Yolk weight comprised 28% of 1-d-old ostrich chick BW and decreased to 12% at 7 d of age. Only 44.4% of the fasted ostrich chick yolk was assimilated over the trial period. Crude protein content of the yolk decreased by 13.2 g daily. Fat content increased by 1.77% daily, whereas total yolk fat weight decreased with 8.91 g daily. Slaughter weight of fed ostrich chicks increased, with yolk weight decreasing by 16.3 g daily. Yolk content for fed ostrich chicks was 26% of BW at 2 d of age. Ostrich chicks absorb 30% of yolk over the first 4 d, 67% after 8 d, and only deplete the yolk after 14 d posthatch. Fasted ostrich chicks absorbed the yolk content at a rate of 28.9 g/d, compared with 22.3 g/d over the first 8 d and 16.3 g/d over the 16 d for fed ostrich chicks. The CP content of the yolk decreased by 6.84 g daily in fed ostrich chicks, whereas fat content of the yolk increased by 1.39% daily, although total yolk fat weight decreased by 6.61 g daily. Yolk weight and total CP decreased faster over the first 7 d in the fasted ostrich chicks compared with the fed ostrich chicks, which indicated that the decrease in yolk weight could be attributed to absorption of protein from the yolk. Fat content decreased faster over the first 8 d from the yolk of the fed ostrich chicks compared with that from the yolk of the fasted ostrich chicks, which could indicate that external feed has a positive influence on the absorption of fat from the yolk content. [ABSTRACT FROM AUTHOR]

Multiflagellate sperm represent a rare defect in mammals and also in the emu where an incidence of only 1% multiflagellate sperm was recorded in semen samples from 15 birds. Biflagellate sperm were the most frequent form of the defect observed, but 3- to 5-tailed sperm were also noted. An association was apparent between multiple tails and macrocephalic sperm, which accounted for 0.6% of multiflagellate sperm. Structural features of the defect were generally similar to those seen in mammals. The duplicated tails shared a single midpiece, which housed supernumerary centriolar complexes, each surrounded by a mitochondrial sheath. A single row of mitochondria separated adjacent centriolar complexes. Elements of the connecting piece (segmented columns, capitellum) appeared normal. The nuclear base appeared flat, staggered, or scalloped depending on the number and depth of additional implantation fossae. Multiflagellate emu sperm of normal head dimensions displayed a widened nuclear base (in the form of an attenuated peripheral nuclear extension) to accommodate the attachment of the additional centriolar complexes. Defective mammalian sperm do not show this modification of the nuclear base as the inherently wider sperm head is able to accommodate the supernumerary centrioles. Although often spiraled around each other, the duplicated principal pieces of the tail were generally separated and free. However, in some cells the proximal parts were collectively bound within the plasmalemma. Multiflagellate sperm appear to have a dual origin with some defective cells originating from incomplete cytokinesis and others as a result of abnormal centriolar duplication., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The accurate assessment of avian sperm abnormalities is hampered by a lack of descriptive data and by the confusing terminology currently in use. Critical appraisal of semen samples from the distal ductus deferens of the emu revealed that two closely related yet separate (distinct) defects previously collectively referred to as "bent sperm" or "crooked-necked sperm" could be identified by light and electron microscopy. Head-base bending typically involved a 180° bend at the base of the nucleus which placed the head and midpiece into close apposition and parallel to each other. No part of the neck or midpiece was involved and bending was restricted exclusively to the base of the nucleus. Incomplete chromatin condensation was always associated with the bend. Disjointed sperm, which superficially resembled "bent" sperm, showed complete separation of the neck from the head-base at the level of the connecting piece. All structural elements of the neck region appeared normal. In both defects the region of contact between the head (nucleus) and the neck/midpiece was enclosed as a unit by the plasmalemma. Both defects were observed to originate in the testis; however, their subsequent expression in the ductus deferens cannot be ruled out. These results confirm that head-base bending of emu sperm represents a head defect, whereas disjointed sperm should be classified as a tail (neck/midpiece) defect., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Differences exist in reproductive physiology between African buffalo (Syncerus caffer), cattle (Bos taurus) and water buffalo (Bubalus bubalis). The aim of this study was to histo-morphologically compare the anatomy of non-pregnant and pregnant uteri of buffalo and cattle. Two non-pregnant uteri and placentae of six pregnant African buffalo were used. Early placentome formation (fetal crown rump length (CRL): 2-17.5 cm) in S. caffer and B. taurus was compared. The endometrium of buffalo uteri comprises round to ovoid, dome-shaped and gland-free caruncles. A predominantly simple columnar epithelium of non-ciliated cells covers caruncular tissue, while, additionally, ciliated cells occur in the epithelium of the intercaruncular areas and within the simple columnar or pseudostratified epithelium of the endometrial glands. During early gestation, multiple placentomes develop. Unlike the placentomes in cattle at similar CRL, buffalo placentomes do not develop a caruncular stalk. The sessile, dome-shaped buffalo placentome has simple, slightly conical villi branching less than in cattle, thus indicating different and less complex feto-maternal interdigitation than seen in the latter. A synepitheliochorial interhaemal barrier can be expected in the buffalo placenta, as the occurrence and ultrastructure of trophoblast giant cells resemble those described in cattle.

The morphology of the gular valve of the Nile crocodile was studied on the heads of eight 2.5-3-year-old commercially raised Nile crocodiles (Crocodylus niloticus). A description of the macroscopic and microscopic features of the gular valve is presented and the results are compared with published information on this species and other Crocodylia. The histological features are supplemented by information supplied by scanning electron microscopy (SEM). Anatomically, the dorsal and ventral components of the gular valve in the Nile crocodile form an efficient seal that effectively separates the oral and pharyngeal cavities consistent with the natural behavior and feeding habits of this animal. The gular valve is more complex in nature than superficial observations would suggest, with the dorsal and ventral folds being complemented by a series of smaller folds, particularly at the lateral fringes of the valve. Histologically, the surface epithelium of the valve demonstrates a transition from the typical stratified squamous epithelium of the oral cavity to that of the respiratory epithelium lining the pharyngeal cavity. The respiratory epithelium is characterized by the presence of ciliated cells and goblet cells and is accompanied by the appearance of large mucus-secreting glands in the underlying connective tissue. The transition between the two epithelial types is marked by the presence of a relatively prominent region where the stratified squamous epithelial cells undergo a gradual transformation into the typical elements of a respiratory epithelium. SEM graphically illustrated the extent of ciliation on both components of the gular valve as well as clearly defining the transition zones between the various types of surface epithelium present. No structures resembling taste receptors were observed in the mucosa of the gular valve., (Copyright 2006 Wiley-Liss, Inc.)

The heads of nine 2.5 to 3-year-old Nile crocodiles (Crocodylus niloticus) were obtained from a commercial farm where crocodiles are raised for their skins and meat. The animals from which these specimens were obtained appeared clinically healthy at the time they were slaughtered. A description of the macroscopic and microscopic features of the tongue of the Nile crocodile is presented and the results are compared with published information on this species and other Crocodylia. The histological features are supplemented by information supplied by scanning electron microscopy. Macroscopic features of interest were the dome shaped structures grouped in a triangular formation on the posterior two-thirds of the dorsum of the tongue. These structures were identified by light microscopy to contain well-developed branched, coiled tubular glands and associated lymphoid tissue. Other histological features included a lightly keratinised stratified squamous surface epithelium supported by a thick layer of irregular dense fibrous connective tissue. Deep to this region was a clearly demarcated adipose tissue core with a dense mass of striated lingual musculature. Localised thickenings were present in the epithelium which were associated with ellipsoid intra-epithelial structures resembling taste buds.

The heads of nine 2.5 to 3-year-old Nile crocodiles (Crocodylus niloticus) were obtained from a commercial farm where crocodiles are raised for their skins and meat. The animals from which these specimens originated were clinically healthy at the time they were slaughtered. A detailed description of the macroscopic and microscopic features of the palate and gingivae of the Nile crocodile is presented and the results are compared with published information on this species and other Crocodylia. The histological features are supplemented by information supplied by scanning electron microscopy. Macroscopic features of interest are the small conical process situated at the base of the first two incisors of the maxilla, the distribution of cobbled units on the palate, and the broad dentary shelf forming the rostral aspect of the mandible. Histologically the palate and gingivae did not differ significantly from each other and both regions showed a presence of Pacinian-type corpuscles. Two types of sensory structures (taste receptors and pressure receptors) were identified in the regions examined, both involving modification of the epithelium and the underlying connective tissue.

Simple testicular cysts are rare in mammals and of unknown aetiology, but dietary conditions have been implicated in this phenomenon in poultry. This study characterises the structural features of simple intratesticular cysts in the ostrich. Seven testes from a total of 15 sexually mature ostriches slaughtered during the breeding season were used. The testes contained multifocal, fluid-filled, unilocular cysts which were lined by a simple squamous or low cuboidal epithelium and surrounded by a thick layer of fibrous connective tissue. The cysts developed within seminiferous tubules and displayed morphological features similar to those reported in man and domestic poultry. The testis parenchyma revealed several foci composed of intermingled normal seminiferous tubules and variably sized intratesticular cysts. The atrophic tubules lay within a mass of hyperplastic, fibroblastic intertubular connective tissue in the proximity of large cysts and their formation appeared to result from hydrostatic pressure exerted by cysts. Morphological evidence supports a continuous process of cyst formation in the affected testis and a concomitant progressive loss of atrophic seminiferous tubules. A pathogenetic scenario of cyst formation and the effect of simple cysts on testicular histology has been proposed. Although the course of this phenomenon remains unknown, its impact on the fertility of this economically important bird deserves closer scrutiny.

While particular attention is paid to the nature and content of anatomy curricula, little has been published about the actual problem topics/concepts experienced by students of anatomy. This information is relevant to modifying existing courses and methods of teaching. The present study thus sought to identify, by means of a questionnaire administered to students of veterinary anatomy, perceived problem topics, the possible reasons for the problems, as well as student suggestions for solving the problems. A wide range of problem topics was identified by this survey, of which neuroanatomy, neurohistology and organogenesis recurred most frequently. A major reason given for the problems experienced was an inability to conceptualise 3-dimensional structures. Students requested more time, more lectures and appealed for a reduction in detail of textual information. Many of the problems experienced by this group of students are reflected in other studies of veterinary, medical and dental students, which suggests the existence of 'universal' problem topics in the various fields of anatomy. We believe that these universal problem topics exist in many anatomy courses, despite the application of innovative teaching methods and advanced audio-visual technologies. Only by identifying these topics can suitable strategies (within the constraints of the particular curriculum) be devised to resolve them.

Change in medical curricula is a worldwide trend. Concomitant with this is a change in the role of the microscope and its contribution to a student's career. In this questionnaire-based study the perceptions of medical, dental and veterinary students to microscopy and alternative forms of histology tuition, as well as the role of microscopy in their future careers, was assessed. Veterinary students indicate a strong preference for the microscope and microscopy training due to the importance of the microscope in their chosen career, whilst medical and dental students are somewhat ambivalent. However, the students would not choose to eliminate the microscope entirely from their studies.

An accurate description of the number, location and relative position of the air sacs and their diverticula in the ostrich is essential for a better understanding of the pathogenesis of air sacculitis in this bird. The air sacs were studied in ten ostriches of varying ages by latex or silicone casting of the respiratory tract and dissection. Results revealed that the air sacs of the ostrich conform to the general pattern in birds. Cervical, lateral and medial clavicular, cranial and caudal thoracic, and abdominal air sacs are present. The left and right medial clavicular air sacs fuse with each other ventrally to the trachea to form a single, median compartment. A unique, large gastric diverticulum which covers the caudal aspects of the proventriculus and gizzard originates from the median compartment of the clavicular air sac. The lateral clavicular air sacs and their diverticula are similar to those of other bird species, with the exception that humeral diverticula are absent. Both abdominal air sacs are relatively small, with the left sac being the larger. Perirenal and femoral diverticula, similar to those found in other bird species, are present. However, the entire femur is aerated by the femoral diverticulum which also forms a large, subcutaneous division caudally and caudo-laterally to the femur. The presence of this subcutaneous part has practical implications for injury and intramuscular injections. The number and location of ostia connecting the air sacs to the bronchial tree are generally similar to those reported in other bird species.

We have characterized for the first time the proteins of two different species of palaeognathous birds, Struthio camelus australis (ostrich) and Nothoprocta perdicaria sanborni (Chilean tinamou). Similar to what had been previously reported in neognaths, the electrophoretic mobility, amino acid composition, and primary structure of the main protamine (P-II) component of these two species of birds are similar. However, in contrast to neognathous birds, the protamines from paleognaths display a higher electrophoretic mobility and a significantly different amino acid composition and protein sequence. The sperm and the main protamine component P-II from the ostrich reveal structural and compositional characteristics intermediate between neognathous birds and reptiles. The marked differences between the protamines and sperm structure of neognaths and paleognaths provide support to a phylogenetic relationship between neornithine birds in which these two groups represent two separate phylogenetic lines. Furthermore, these results shed some additional light on the controversial origin of birds. They provide further molecular support to the fossil record that suggests that reptiles and birds are closely related.

Sperm-storage tubules have been described in a number of species of birds. The presence of these tubules in the Rhea has been mentioned, but no description of these structures in ratites is available. The purpose of this study was to determine the presence and morphology of sperm-storage tubules in the vagina of the ostrich. The study was performed with the use of conventional light- and electron-microscopic techniques. Sperm-storage tubules were located in a 200-mm-wide band of the vagina adjacent to the utero-vaginal junction. The tubules were mostly branched and slightly coiled and lined by columnar epithelial cells. The cells contained a basal nucleus and displayed extensive apical junctional complexes. TEM revealed sperm in all the tubules examined.

When female Saccostomus campestris are stressed during pregnancy they may resorb part of the litter. Resorption can take place on more than one occasion during the same pregnancy without affecting the development of the rest of the litter. The last resorption may be initiated as late as 72-48 h before parturition. No other rodents with a similar gestation appear to resorb at this stage. Resorbing fetuses are isolated within uterine compartments from viable fetuses. Ossification occurs at a comparatively late stage of pregnancy in Saccostomus campestris, and there is a lag-period in fetal growth exactly 72-48 h before parturition. These factors may facilitate late resorption in this species. Factors that may cause stress in this species are most likely environmental; in the present study, dipping of the animal colony to treat for a mite infestation may have induced resorption in some of the females.

The formation and development of the ostrich sperm tail follows the general pattern described for vertebrate sperm but differs in a number of important aspects when compared with other nonpasserine birds. Midpiece formation is characterised by the development of a long (3 microns) distal centriole which determines the length of the midpiece. The distal centriole surrounds a pair of microtubules embedded in a core of dense material. A prominent annulus, which remains stationary during spermiogenesis, demarcates the midpiece/principal piece junction. Ostrich spermatids display similar cytoplasmic densities (chromatoid body, annulus, granulated bodies, reticulated bodies and mitochondria-associated material) to those observed in mammalian spermatids. In the ostrich, however, the chromatoid body is not observed to contribute towards the formation of the annulus while the granulated bodies develop within radial bodies and not in their vicinity as in mammals. Whereas in mammals granulated bodies have been linked to coarse fibre formation they appear to perform a limited function in ostrich spermatids as only rudimentary outer dense fibres are formed. No specific role is attributed to the reticulated bodies but the mitochondria associated material is implicated in the formation of intermitochondrial cement. The formation of the principal piece and end piece of the flagellum is modelled on that of the mammalian spermatid. The axoneme emerges from the free end of the distal centriole and the ribs and longitudinal columns are progressively formed from a layer of amorphous material situated between the axoneme and the plasmalemma. The end piece is formed by an extension of the principal piece consisting of axonemal microtubules closely surrounded by the plasmalemma. The formation of a long distal centriole containing a central pair of microtubules, the stationary nature of the annulus and the presence of a ribbed fibrous sheath around the principal piece distinguishes spermiogenesis in the ostrich and rhea from that of other nonpasserine birds. These features appear to be characteristic of more primitive avian families.

Tibiotarsal rotation in ostrich chicks is a serious problem that accounts for considerable financial loss to ostrich farmers. Serum- and bone-mineral analyses of 20 ostrich chicks with tibiotarsal rotation were compared with serum- and bone-mineral analyses of eight normal ostrich chicks of comparable age, sex and body mass, and raised under identical conditions. The serum-zinc values were significantly higher and the bone-calcium and phosphorus values significantly lower in the affected group than in the group of normal ostrich chicks. The results indicated poor mineralization of bone with subsequent reactive osteoid formation.

The three-dimensional structure and size of ostrich sperm is unknown. In this study, the morphology and dimensions of ostrich sperm were determined by scanning electron microscopy of semen samples obtained from sexually mature males during the breeding season. The results indicate that sperm cells of the ostrich are of the sauropsid type characteristic of non-passerine birds and, in general appearance, resemble those of the chicken, turkey, guinea fowl, budgerigar and tinamou. They differ from tinamou sperm, however, in that they do not show a small bump at the tip of the acrosome. Ostrich sperm are shorter (69.6 microns total length) than those of the chicken, turkey and guinea fowl, but longer than those of the budgerigar. A lack of information makes it impossible to compare the dimensions of ostrich sperm with those of other ratites such as the rhea. In ostrich and guinea fowl, the sperm head is proportionately longer than that of the chicken, turkey and budgerigar as determined by tail to head ratios. Two distinct groups of ostriches could be distinguished on the basis of differences in the length of various sperm cell components. This may reflect persistent genetic (subspecies) variations in the domestic ostrich population.

The origin and relationships of the tinamous (Order Tinamiformes), ratites (Order Struthioniformes, Rheiformes, Casuariiformes, Apterygiformes) and birds of the order Galliformes and Anseriformes is the subject of much debate and it has been suggested that the ultrastructural analysis of a wide variety of avian sperm may provide information relevant to this problem. This paper describes the fine structure of ostrich sperm and compares the results with published information for other non-passerine birds. Ostrich sperm display a short, conical acrosome which covers the tapered tip of the long, cylindrical nucleus. A nuclear invagination housing an acrosomal rod extends deep within the karyoplasm. A centriolar complex is situated beneath the head and consists of a short proximal centriole and a long (3.0 microns) distal centriole which extends the complete length of the midpiece. The central cavity of the distal centriole contains a pair of microtubules embedded in a rod of electron-dense material. The midpiece is surrounded by a mitochondrial sheath. Concentrations of fine granular material are present between the mitochondria. The principal-piece of the tail is demarcated from the midpiece by a distinct annulus and characterized by a ribbed fibrous sheath enclosing a typical axoneme. Rudimentary coarse fibres are observed between the fibrous sheath and the doublet microtubules of the axoneme in the proximal region of the principal-piece. The end-piece contains a disorganized collection of axonemal microtubules. Ostrich sperm differ in a number of respects from that of other non-passerine birds (the absence of a typical perforatorium; the presence of a ribbed fibrous sheath; a deep nuclear invagination; the structure and length of the distal centriole) but show a close similarity to sperm of the rhea and crested tinamou, both representatives of primitive avian families. These observations add further support to the theory that the ratites and tinamous constitute a monophyletic group. The evidence presented also reinforces the hypothesis that the ratites were the first group to branch off from the main avian stem, to be followed by the Galliformes & Anseriformes. Although it was impossible to determine whether the sperm of the tinamou are more "primitive" than those of the ostrich or rhea, it is clear that ostrich and rhea sperm are closely allied and distinct from tinamou sperm.

Spirally arranged bundles of sub-endothelial smooth muscle enfold the small to medium-sized submucosal veins in the equine ileocecal junction. The muscle bundles, accompanied by the endothelial lining, bulge into the lumen of the vessels, partly occluding the latter. Transmission electron microscopy of the muscle cells reveals features consistent with vascular smooth muscle ultrastructure. It is proposed that the throttling effect of the muscle bundles causes engorgement of the submucosal venous plexus, which then assists in the closing of the ileocecal orifice.

The ileocaecal junction mucosal surface morphology of 5 horses and 1 donkey was examined using scanning electron microscopy and light microscopy. Based on differences in surface morphology, the junction could be divided into 4 distinct regions. The distal extremity of the ileum was characterized by the presence of typical finger-like villi followed by a narrow zone displaying short, stubby villi which gradually merged into a 3rd region representing the true transitional zone between the small and large intestine. In this region the villi fused, forming low ridges arranged in circular, semi-circular or S-shaped patterns. Many of the fused villi were indented at the tips giving these structures a doughnut-like appearance. The caecal portion of the ileocaecal junction formed the 4th region and was characterized by the absence of villi and the occurrence of regularly spaced crypt openings each surrounded by a slightly raised circular mound.