SEC. IV ANATOMY OF BIRDS 321 



ductioii.^ AVe have here to consider the permanent as distinguished 

 from the transitory kidneys, and may then recur to the subject of 

 generation. 



The Kidneys (Lat. rencti, Engl, refuu, adj. renal ; Figs. 103, 104, 

 a; 105, x) difter much from those of mammals in physical 

 characters, though identical in function — that of straining off from 

 the blood certain deleterious substances in the form of urea ; 

 whence they are sometimes called emulgent organs. Their office of 

 purification is analogous to that of the lungs, which decarbonise the 

 blood, and to some extent vicarious, as is that of excretory organs 

 in general. As the lungs are closely bound down to the thoracic 

 region of the trunk, so are the kidneys impacted in the pelvic 

 region, being moulded to the many sacral inequalities of surface. 

 They are paired, but sometimes connected across the median line 

 by renal tissue ; they have no special renal artery, but derive their 

 blood from various sources ; and blood from them takes part in the 

 hepatic portal system, no reniportal being accomplished. They have 

 little or nothing of the particular mammalian configuration which 

 has made " kidney-shaped " a common descriptive term ; being 

 elongated, somewhat parallel-sided, and rectangular, flattened bodies, 

 lobated into a few large compartments, and lol)ulated into many 

 lesser divisions ; their figure depends much ujjon that of the pelvis. 

 They are very dark coloured, rather soft, easily lacerable, and 

 appear to the naked eye to be of a granular substance, without 

 distinction of "cortical" and "medullary" portions. Nor is there 

 any " pelvis " of the kidneys in which the uriniferous tubules empty 

 together by numerous ducts as in a common basin. Each iireter 

 (Figs. 103, h; 104, e; 105, y) or excretory duct is formed by 

 reiterated reunion of the tuhidi uriniferi, after the manner of a 

 pancreatic duct ; each ureter passes down behind the rectum and 

 opens into the lower back part of the cloaca — much like a 

 mammalian ureter into the base of the bladder. The original 

 cavity of the allantois remains to furnish no more of a urlnav)/ 

 hkulder than some special dilatation of the cloaca represents ; but 

 this rudimentary bladder, as distinguished from the urogenital 

 sinus in which the ureters terminate alongside the sperm-ducts, is 

 well marked in some birds ; being in the ostrich, for example, a 

 considerable enlargement of the cloaca between the termination of 



■•■ The matter may be further illustrated by the two figures borrowed from Owen 

 (after Miiller). In both figures, the large dark masses, a, are the permanent kidneys, 

 whose ducts, b in Fig. 103, e in Fig. 104, are the ureters, emptying into the cloaca. In 

 Fig. 103, male, c is the Wolffian body, whose duct, d, persists as the sperm-duct, con- 

 veying semen from e, the testis. In Fig. 104, /; is the Wolffian bod)', whose duct,/, dis- 

 appears ; and g is the Miillerian duct, becoming the oviduct, to convey the egg from c, 

 the ovary. Thus e, Fig. 103, and c, Fig. 104, are the homologous genital glands, becoming 

 either testis or ovary ; but the sperm-duct, d, Fig. 103, is not the oviduct, g, Fig. 104. 



Y 



