788 SPECIAL PHYSIOLOGY. 



The kidneys of many Mammalia exhibit the typical bean- shape, but they are 

 often more rounded than in Man, as in the sheep, pig, and dog. They are 

 sometimes more or less lobulated. In the ox, the kidney is sublobulated, being 

 marked by fissures between the pyramids, which form the lobules, remaining, 

 however, united beneath the divided cortical portion. In certain Carnivora, 

 as in otters, seals, and bears, the pyramids, each covered by its own cortical 

 layer, are separated by deeper fissures, into which even the capsule of the kid- 

 ney penetrates, so that the lobules form clusters of distinct polyhedral masses 

 attached to the separate infundibula of a much-ramified ureter. The kidney 

 is most deeply lobulated in the Cetacea. In the early embryonic condition of 

 this organ in all Mammalia, the lobulated character is present ; in the Cetacea 

 and certain Carnivora, it persists, and forms the so-called compound kidney ; 

 in other animals, as in the ox, the lobules partly coalesce ; lastly, in the sheep, 

 dog, and Man, they completely unite, as development advances. Indeed, a 

 lobulated or ramihed condition seems to be a less developed form of many 

 glands than the massive shape, as is illustrated by the liver, pancreas, spleen, 

 and thymus in animals. Lobulation of the lung, however, is a sign of higher 

 development. Subordinate peculiarities exist as to the mode in which the pa- 

 pill ge of the kidneys are connected with a simple or much-subdivided ureter. 



In Birds, the kidneys no longer present an obvious distinction into a cortical 

 and medullary substance, and the gland tissue is much less firm than in the 

 Mammalia. In Birds, these organs are of considerable length, occasionally 

 blended together, in places, across the middle line ; they extend from the pos- 

 terior border of the lungs, down to the lower eud of the rectum, and are 

 moulded into recesses in the bones of the lower part of the spinal column. The 

 kidneys of Birds are, therefore, slightly lobulated. The uriniferous tubuli of 

 each lobule are arranged in bundles or tufts, which end in the outer or super- 

 ficial part, by dichotomous tubes ; the symmetrical ureters proceed from the 

 abdominal surface of the glands, receiving the uriniferous tubules directly, 

 without the formation of infundibula, or of a pelvis. They open below, in the 

 upper and back part of a dilatation found at the lower end of the alimentary 

 canal, named the cloaca, where there is a sort of recess, which has been re- 

 garded as representing an imperfect bladder. 



In Reptiles, the kidneys are very large, occupy the same general position as 

 in Birds, and are usually of great length. In the turtles, tortoises, and liz- 

 ards, they are symmetrical, and fixed to the lumbar and pelvic regions ; but 

 in Serpents, the right kidney is placed higher than the left, as if for con- 

 venience ; they extend along the greater part of their elongated and flexible 

 spine. The kidneys present no distinction of cortical and medullary sub- 

 stance ; but they are deeply lobulated, and loosely connected with the sur- 

 rounding parts. The ureters are long and narrow, and end in a sort of 

 cloaca. The tubuli uriniferi are reduced to convoluted, or even short, straight 

 csecal tubes, arranged in converging bundles, or placed transversely. In the 

 crocodile, the convoluted tubuli are so distinct as to appear like a cortical 

 layer. 



In Amphibia, the kidneys are flat and broad at their hinder end, but become 

 very narrow at their anterior part, and thus show an approximation to their 

 form in Fishes. Numerous ducts proceed from their inner border, to a long 

 slender ureter, which opens into the cloaca. 



In Fishes, the kidneys are proportionally large ; they vary in shape in differ- 

 ent species, but, as a rule, are narrow, and of extreme length, being attached 

 beneath the bodies of the vertebrae, along the whole or the greater part of the 

 abdominal cavity, above the air-bladder when that organ exists. There is no 

 distinction of cortical and medullary substance, and tufts of slightly tortuous 

 urinary tubuli, or completely straight csecal tubes, end at once in narrow elon- 

 gated ureters, which usually open on each side, into the cloaca! portion of the 

 rectum, but which sometimes first coalesce. In the low Myxinoid fishes, the 

 upper portion of the kidneys is much attenuated, and presents a complete un- 

 folding of the gland structure ; the tubuli, instead of being long and aggregated, 

 are short, distinct, and commence by little dilatations, into which the Mal- 

 pighian glomeruli project. In the amphioxus, the kidney has not been distinctly 

 made out, though it is probably represented by a narrow gland-like mass placed 

 near the abdominal pore. 



