The pecten oculi is a structure peculiar to the avian eye. Three morphological types of pecten oculi are recognized: conical type, vaned type and pleated type. The pleated type has been well studied. However, there exists only scanty data on the morphology of the latter two types of pectens. The structure of the vaned type of pecten of the ostrich, Struthio camelus was investigated with light and electron microscope. The pecten of this species consists of a vertical primary lamella that arises from the optic disc and supports 16-19 laterally located secondary lamellae, which run from the base and confluence at the apex. Some of the secondary lamellae give rise to 2 or 3 tertiary lamellae. The lamellae provide a wide surface, which supports 2-3 Layers of blood capillaries. Pigmentation is highest at the distal ends of the secondary and tertiary Lamella where blood capillaries are concentrated and very scanty on the primary and the proximal ends of the secondary lamella where the presence of capillaries is much reduced. In contrast to the capillaries of the pleated pecten, the endothelium of the capillaries in the pecten of the ostrich exhibits very few microvilli. These observations suggest that the morphology of the pecten of the ostrich, a flightless ratite bird is unique to the pleated pecten and is designed to meet the balance between optimal vision and large surface area for blood supply and yet ensuring it is kept firmly erect within the vitreous.

Aims: The even‐hoofed, unguligrade tylopods display a well‐developed eponymous footpad that absorbs most of the body weight in locomotion and is particularly adapted to the sandy ground surface of the natural environment of dromedaries. Considering the drastic changes in temperature occurring in the desert sand, specialised thermoregulatory vascular and nervous structures are to be expected in the modified pododerma of this footpad. Therefore, the aim of the study was to demonstrate the angioarchitecture of the camelid footpad and to detect specialised vascular structures related to these specific functions.Material and Methods: Corrosion casting of fore and hind feet of dromedaries (Camelus dromedarius); scanning electron microscopy of micro‐corrosion castsResults and Discussion: The dense angioarchitecture of the dromedary footpad, like that of unmodified skin, can be subdivided into separate plexus arranged at different levels: a subcutaneous plexus, a profound dermal plexus, a superficial dermal plexus and a subepidermal plexus.The subepidermal blood vessels run very close to the dermo‐epidermal borderline and thus the subepidermal angioarchitecture consists of densely vascularised conical papillae comprised of centrally situated papillary arteriole and venule ensheathed in a dense subepidermal capillary network. At the tip of the papillae, the central papillary arteriole and venule form a peripheral capillary loop, acting as a thoroughfare channel. This dermal angioarchitecture of the dromedary footpad is comparable to the papillary system described in the bulbs of the highly specialised digital end organs of many other odd‐ and even‐hoofed mammals, particularly the equine hoof and the bovine claw.Within the subcutaneous and the deep dermal plexus of the dromedary foot pad, unique glomus‐like vascular structures were detectable, presumably associated with cutaneous thermoregulation as described for the unmodified hairy skin.

The intestinal morphology of 7-week-old pigs was investigated by light (LM) and scanning electron microscopy (SEM). The piglets were fed either a semisynthetic or a cereal-based diet. The shapes of the intestinal villi and crypts of the duodenum, jejunum and ileum were examined. The villi were predominantly tongue-shaped. In the duodenum they were also ridged, branched and folded, and in the jejunum they were also leaf-like and ridged. At places with lymph follicles, the surface of the ileum was rugged with meandering fold-like villi. The crypts of the three segments of the small intestine were mainly coiled and sometimes branched. A novel morphometric evaluation method was introduced using the enlargement factors of each villus and crypt surface. The enlargement factor for the villus surface of the duodenum, jejunum and ileum was 3.13, 3.72 and 2.71, respectively. The factor for the crypt surface of the duodenum, jejunum and ileum was 9.07, 8.94 and 6.53, respectively. Furthermore, the relative proliferation rate and the epithelial renewal index were calculated for the first time. The relative proliferation rate of the duodenum, jejunum and ileum was 32.88, 34.78 and 50.77 proliferations per mm crypt perimeter, respectively. The diets consumed had an influence on the epithelial renewal index being higher for piglets fed the cereal-based diets.

The tongue specimens were collected from Beni-Adi slaughterhouse, near Assiut. They were fixed by injecting 2.5% paraformaldehyde and 2.5% glutaraldehyde in 7.2 phosphate buffer (pH 7.2) through the lingual artery. Pieces of tissue from several areas bearing the lingual papillae were cut and prepared for light microscopy and scanning electron microscopy. The Connective Tissue Core (CTC) of the filiform papillae was found to be in three forms, i.e. the filament-shaped, broad and pyramidal type. The surface of the CTC of the conical papillae was studded with secondary process. Their apeces were bifurcated. The CTC of the fungiform papillae was also seen in the tongue-shape. At their base the CTC detached very large secondary papillae which were arranged in a scaly manner. The surface of the CTC of the vallate papillae (6-11 in number) was studded with different types of secondary processes which were completely different in shape, size and length.

The pecten oculi is a highly vascularized and pigmented organ that overlies the optic disc and projects into the vitreous body in the avian eye. First reported over 300 years ago, its function(s) remains a puzzle to ornithologists, ophthalmologists and anatomists. Morphometric study of this unique organ was undertaken in birds exhibiting apparently different visual acuities, namely two species of diurnal birds (the ground-dwelling domestic fowl Gallus gallus var. domesticus and a highly active predator bird, the black kite (Milvus migrans) and a nocturnal bird (the spotted-eagle owl Bubo bubo africanus). The volume of the owl's eye was 4.8 and 2.2 times larger than that of the fowl and the kite, respectively. However, the pecten of the fowl consisted of more pleats (16-18) compared to the kite (12-13) and the owl (5-6). The volume of the pecten of the kite was 1.4 and 2.7 times larger than that of the fowl and the owl, respectively (P < 0.05). Similarly, the surface area of the pecten of the kite was 2.6 and 4 times larger than that of the fowl and owl, respectively (P < 0.05). The volume density of blood vessels (lumen and wall) in the pecten of the kite, fowl and owl comprised 67.7%, 66.9% and 62.6%, respectively, the pigmented tissue constituting the rest. Both the volume density and the volume of the blood in the pecten were higher in the diurnal birds (kite, fowl) than the owl (P < 0.05). The surface area of the capillary luminal surface was 1.7 and 5.3 times higher in the kite than in the fowl and the owl, respectively (P < 0.05). These results suggest that the functional morphology of the pecten correlates with the life-style of the bird and with functional need, and lends further support to the nutritive role of the pecten.

The luminal surface of the pecten oculi of the black kite (Milvus migrans), a diurnally active bird of prey, was examined by scanning electron microscopy. In this species the blood vessels are generally of two types, the small-calibre capillaries and the large-calibre afferent and efferent vessels. The luminal surface of the efferent blood vessels possesses a few low microplicae. Conversely, the luminal surface of the afferent blood vessels is characteristically smooth except at the cell junctions and at the point of entry into the capillaries. The cells junctions are marked by low ragged ridges while the luminal surface is studded with low sparse pleiomorphic microprojections at the point of capillary emergence. The luminal surface of the blood capillaries is characterised by a labyrinth of closely disposed microplicae that projects into the lumen. These microplicae show no particular orientation with respect to either the longitudinal or transverse axis of the capillary. Instead, they are diffusely orientated. It is conjectured that such a heterogeneous design of the endothelium in the blood vessels of the pecten oculi has developed in order to augment the role of the pecten in the transport of nutrients to the avascular neural retina by an energy saving diffusion process. The process through which the design of the microfolds affects haemodynamics and their putatite role in facilitating the delivery of nutrients are discussed in the perspective of the available data.

The structure of the capillary endothelium in the pecten oculi of the domestic fowl was investigated by scanning and transmission electron microscopy. Scanning electron microscopy results demonstrated the existence of a vast array of irregular microplicae that projected from the luminal surface of the capillary endothelium. In between these microplicae were numerous crevices. The microplicae were closely packed and showed no preferred orientation regarding either the longitudinal or transverse plane of the capillaries. Transmission electron microscopy revealed the section profiles of the microplicae: their tortuity, branching, interdigitations and the magnitude of the crevices contained. The endothelial cytoplasm exhibited a few mitochondria and micropinocytotic vesicles. The apparent set-up of the luminal plasmalemmal infoldings seemed to be designed for effecting impedance to the pectineal blood flow and thereby facilitating passive permeation of blood-borne nutrients to the inner neural retina. The reasons of such passive transport operation mediated by the endothelial microplicae of the avian pecten oculi are discussed in the perspective of the existing literature.

The three-dimensional architecture of the connective tissue core (CTC) and the epithelial cell layer of the mucous membrane in the first and second compartments of the camel's forestomach was studied with the scanning EM. The samples were fixed in 2.5% glutaraldehyde and then immersed in 3N HCl solution for a period of 20 days at 4 degrees C. Thereafter, the epithelial cell layer was removed gently from the underlying CTC, both were dried in Peldri II, sputter-coated with gold and investigated with Zeiss DSM 950. Unlike in common ruminating animals, the mucous membrane (M.M.) of the forestomach in the camel is not arranged in complicated folds, crests or papillae. However, the CTC in both the first and second compartments (rumen and reticulum) was found to be arranged in four different ways: 1) Parallel ridges (55-166 mu m high) that alternate with grooves. Some of the ridges were projected by cone like structure. 2) Low, cone-like elevations (free cones) 27-66 mu m high. 3) Folds arranged in a network-like way. 4) Narrow undulations without.

The pecten oculi of the black kite (Milvus migrans), a diurnally active bird of prey, has been examined by scanning electron microscopy. In this species the pecten consists of 12 highly vascularised pleats, held together apically by a heavily pigmented 'bridge' and projects freely into the vitreous body in the ventral part of the eye cup. Ascending and descending blood vessels of varying calibre, together with a profuse network of capillaries, essentially constitute the vascular framework of the pecten. A distinct distribution of melanosomes is discernible on the pecten, the concentration being highest at its apical end, moderate at the crest of the pleats and least at the basal and lateral margins. Overlying and within the vascular network, a close association between blood vessels and melanocytes is evident. It is conjectured that such an association may have evolved to augment the structural reinforcement of this nutritive organ in order to keep it firmly erectile within the gel-like vitreous. Such erectility may be an essential prerequisite for its optimal functioning, as well as in its overt use as a protective shield against the effects of ultraviolet light, which otherwise might lead to damage of the pectineal vessels.

The conjunctiva of the dog has a smooth surface on the inside of the upper and lower lid and of the bulbus oculi. In these areas the conjunctiva is covered by a stratified squamous epithelium, the polygonal surface cells of which have microvilli and microplicae which are different in number and show a great variety of shapes. In the passage towards the fornix conjunctivae a stratified cuboidal epithelium is to be discerned. In the fornix itself, the conjunctiva is arranged in small folds which are protruded by goblet cells and the openings of lacrimal glands. Here a stratified cuboidal or columnar epithelium can be observed which at the electron microscopic level shows in all epithelial layers — mostly however in the stratum superficial — morphological signs of enhanced metabolic activities. The bulbar surface of the third eyelid which is covered by a stratified squamous epithelium has a threedimensional moulded pattern of pads and grooves. The structure of the conjunctival epithelium to some extend is age dependent.

The conjunctiva of the dog has a smooth surface on the inside of the upper and lower lid and of the bulbus oculi. In these areas the conjunctiva is covered by a stratified squamous epithelium, the polygonal surface cells of which have microvilli and microplicae which are different in number and show a great variety of shapes. In,the passage towards the fornix conjunctivae a stratified cuboidal epithelium is to be discerned. In the fornix itself, the conjunctiva is arranged in small folds which are protruded by goblet cells and the openings of lacrimal glands. Here a stratified cuboidal or columnar epithelium can be observed which at the electron microscopic level shows in all epithelial layers - mostly however in the stratum superficiale - morphological signs of enhanced metabolic activities. The bulbar surface of the third eyelid which is covered by a stratified squamous epithelium has a threedimensional moulded pattern of pads and grooves. The structure of the conjunctival epithelium to some extend is age dependent.

The conjunctiva of the dog has a smooth surface on the inside of the upper and lower lid and of the bulbus oculi. In these areas the conjunctiva is covered by a stratified squamous epithelium, the polygonal surface cells of which have microvilli and microplicae which are different in number and show a great variety of shapes. In the passage towards the fornix conjunctivae a stratified cuboidal epithelium is to be discerned. In the fornix itself, the conjunctiva is arranged in small folds which are protruded by goblet cells and the openings of lacrimal glands. Here a stratified cuboidal or columnar epithelium can be observed which at the electron microscopic level shows in all epithelial layers--mostly however in the stratum superficiale--morphological signs of enhanced metabolic activities. The bulbar surface of the third eyelid which is covered by a stratified squamous epithelium has a three-dimensional moulded pattern of pads and grooves. The structure of the conjunctival epithelium to some extend is age dependent.

The ontogeny of gastrin- and somatostatin-containing cells in the pyloric gland region of the abomasum was studied in bovine fetuses, newborns and adults, using immunohistochemical techniques. A clear-cut developmental increase in the two kinds of endocrine cells could not be observed. The region of the lesser curvature displays more D and G cells than the greater curvature. Cells of both open and closed types are found from the earliest stages examined and continue to be present throughout the complete differentiation of the pyloric mucosa.