The morphological characteristics of the antebrachiocarpal joint of the cheetah (Acinonyx jubatus).

A morphological study of the structures of the antebrachiocarpal (AC) joint of the cheetah was carded out by dissection of eight forelimbs obtained from four adult cheetahs culled from the Kruger National Park, Republic of South Africa. The aim was to evaluate the deviations of this joint from the normal feline pattern and to consider their possible relationship to the cheetah's adaptation to speed. Although published data on the AC joint of the other felids show general resemblance to that of the cheetah, there are nevertheless slight, but significant variations and modifications which tend to suggest adaptation to speed. The shafts of the radius and ulna of the cheetah are relatively straight and slender, with poorly developed distal ends. The ulnar notch is reduced to a very shallow concavity while the corresponding ulnar facet is a barely noticeable convexity, separated from the distal ulnar articular facet by an ill-defined groove. The movement of the distal radio-ulnar joint is highly restricted by the presence of a fibro-cartilaginous structure and a strong interrosseous membrane, limiting pronation and supination normally achieved by the rotation of the radius around the ulna. The extensor grooves at the distal extremity of the radius are deep and narrow and are guarded by prominent ridges. A thick extensor retinaculum anchors the strong extensor tendons in these grooves. The distal articular surface of the radius is concave in all directions except at the point where it moves into its stylold process. At this point it is convex in the dorsopalmar direction, with a surface that is rather deep and narrow. The proximal row of carpal bones presents a strongly convex surface, which is more pronounced in the dorsopalmar direction with the greatest convexity on the lateral aspect. Medially, there is a ridge-like concavity across the base of the tubercle, which rocks on the flexor surface of the radius, limiting excessive flexion as well as restricting lateral deviation of the AC joint.

Closure of the ductus arteriosus of indigenous South African goats at high altitude.

The closure of the ductus arteriosus (DA) of 31 indigenous South African goats, whose ages ranged from 30 days prenatal to 60 days postnatal, were studied at an altitude of 1,514 m above sea level by vascular injection as well as histologically and ultrastructurally. The vascular injection results showed that functional occlusion started from the pulmonary end of the DA in kids 6 days old and progressed to the aortic end in kids 8 days old. Histologically, anatomical obliteration was observed in kids from 35 days of age. The functional closure was preceded by enlargement of the subendothelial region, progressive intimal thickening, presence of subendothelial vacuolization and endothelial detachment. There was radial orientation of the subintimal smooth muscle cells and subsequent migration towards the intima. The inner tunica media contained mast cells and areas of cytolysis. Following functional closure, the subendothelial region showed migrating subintimal smooth muscle cells with extensive cytoplasmic processes and, ultrastructurally a fragmented internal elastic lamina. In 15-day-old kids there were prominent, progressively enlarged cisternae of the rough endoplasmic reticulum and numerous free, dispersed ribosomes. In kids 19 and 25 days old, there was, additionally, rarefaction of the cell cytoplasm and appearance of intracellular myofibrils and extra cellular collagen in the surrounding amorphous matrix, which culminated in the complete anatomical closure of the DA in 35-day-old kids.

The origin and pattern of distribution of the posterior intercostal arteries in the baboon (Papio ursinus).

The posterior intercostal arteries of six female and four adult male baboons (Papio ursinus) were investigated by latex injection and subsequent dissection to determine their origin and pattern of distribution. Basic morphological and functional similarities with that of man could provide some base-line data pertinent to future experimental studies in the areas of thoracic aortic aneurysm and aortic atherosclerotic lesion in man. Basic similarities were observed between the baboon and man in the number of intersegmental arteries, the origin of the first two pairs of posterior intercostal arteries, and the anastomosis between the superior intercostal and the third posterior intercostal arteries. However, the baboon showed a craniocaudal sequence of paired orifices giving rise to paired arteries; orifices with incompletely divided septum giving rise to paired arteries; single orifices leading to a common trunk, which finally gives rise to paired arteries; and single orifices opening into single arteries. In addition, there was a craniocaudal decrease in the distance between any given pair of intercostal arteries and an increase in the spacing between adjacent pairs of intercostal arteries. Where a single artery supplied one side of the intercostal space, the contralateral side received a collateral branch, either from the preceding or succeeding intercostal artery. Though the basic organisation of the origin and distribution of the posterior intercostal arteries in the baboon is similar to that of man, the differences observed in the baboon might be attributed to factors such as body size, mode of activity, and even the phylogenetic level of development of the baboon.

Postnatal closure of the ductus arteriosus in West African dwarf goats.

Fifteen West African dwarf goats aged between 0 and 42 days were used to study the closure time of the ductus arteriosus using dye injection and histological techniques. The ductus arteriosus appeared haemodynamically patent in kid goats 0 to three days old. There was a progressive contraction of the smooth muscle cells of the wall of the ductus from birth, resulting in the obliteration of the lumen in four and six days at the pulmonary and aortic ends, respectively. This contraction phase was followed by disruption of the luminal endothelium, intimal thickening and necrosis of smooth muscle cells in goats nine to 18 days old. Beyond 21 days there was connective tissue formation resulting in the permanent sealing of the ductal lumen in goats 28 to 33 days old. Although lumina of varying sizes were observed in histological sections of the ductuses of four- to 32-day-old goats, these were haemodynamically insignificant. The results suggest three phases in the closure of the ductus arteriosus of West African dwarf goats which was completed between 28 and 33 days.

Persistent Bergmeister's papilla in a lamb.

The occurrence of Bergmeister's papilla around a persistent hyaloid artery in a ten-week old Suffolk lamb has been reported and its possible genesis is discussed.

Retinal vein diameter during reversible upper respiratory bypass.

A reversible tracheal cannula was implanted in 14 Rambouillet sheep so that the sheep could breathe normally through the nostrils when the 'flow-through' insert was in place or through the tracheal opening when the 'bypass' insert of the cannula was in place. The outer diameter of the superotemporal retinal vein increased significantly in size during nasal bypass breathing compared to normal nasal breathing. Anteroposterior histological sections of the retina and optic disc revealed disc elevation and marked venous engorgement during nasal bypass breathing. These results suggest that a possible increase in the cerebrospinal fluid pressure during nasal bypass breathing must have caused a corresponding increase in optic nerve tissue pressure resulting in axoplasmic flow stasis and swelling of the optic nerve axons in the prelaminar area of the optic disc. The swollen axons apparently caused the compression of the thin-walled retinal veins resulting in venous engorgement.

Effect of reversible upper respiratory bypass on the electroretinogram in sheep.

Ten Rambouillet ewes (2 groups of 5 each) were surgically implanted with a reversible tracheal bypass cannula constructed so that the sheep could breathe normally through the nostrils when the flow-through insert was in place or through the tracheal opening when the bypass insert was adjusted. In 1 group, an electroretinogram recorded an increased amplitude and decreased duration of the b wave during bypassed breathing. When the ewes were allowed to breathe simultaneously through the tracheal opening and nostrils, the b-wave amplitude was decreased, compared with the amplitude during normal nasal breathing alone. Several recordings for individual breathing phases were consistent for each animal. In the 2nd group, arterial blood gas analysis showed no differences in the partial pressures (PCO2 and PO2) during both breathing phases. Seemingly, functional elimination of the upper respiratory cooling of venous blood influences the heat exchange in the ophthalmic plexus and cavernous sinus, resulting in relatively warmer blood reaching the eye.