348 



AVES. 



trunks to the branches, are seen to become con- 

 joined in pyramids, which adhere to the 

 branches of the ureter, are sent out in the gyri 

 of the lobules, and are outspread in a pinnatifid 

 figure on the surface, one next another, and 

 ultimately terminate in blind, rounded, but not 

 dilated extremities. The branches from the 

 convoluted lobules unite dichotomously, and 

 ultimately escape by a single duct the ureter. 

 The arteries and veins of the kidneys have 

 already been described ; a difference of opinion, 

 however, prevails as to the course of the blood 

 in the veins which pass from the lower end of the 

 kidneys (at v,Jig. 171) to the hypogastric vein 

 (z). Jacobson considers that the venous blood 

 is carried into the kidney by these veins, for the 

 purpose of afford ing the material for the urinary 

 secretion, analogous to the portal vein in the 

 liver ; but Cuvier regards these veins as having 

 the same function as those which come from 

 the upper ends of the kidneys, and that they 

 return the blood from the lower ends of the 

 kidneys to aid in the formation of the portal 

 vein. Nicolai* also opposes the doctrine of a 

 venous circulation in the kidneys of Birds. 

 In favour of Jacobson's theory is the small 

 size of the renal arteries, in consequence of 

 which the kidneys are not more coloured 

 than the liver, when the arterial system is in- 

 jected from the aorta, and the disproportionate 

 size of the veins, together with the analogy of 

 the cold-blooded ovipara, in which the exist- 

 ence of a secreting system of veins in the kid- 

 neys is now generally admitted. 



The ureter (y,fg. 163, 182; h, h,jig. 176) 

 has the same structure as in the mammalia. It 

 is continued down along the anterior surface of 

 the kidney towards the mesial side ; here and 

 there imbedded in its substance, forming a 

 series of dilatations corresponding to the prin- 

 cipal lobes or enlargements of the gland, and 

 receiving the branches of the tubuli uriniferi as 

 it passes along. But these slight reservoirs do 

 not present any parts corresponding to the 

 mammillae and their infundibula of mam- 

 malia. Below the kidney the ureters pass be- 

 hind the rectum, becoming connected to, and 

 after a short distance involved in its coats; 

 they ultimately terminate upon valvular emi- 

 nences, in a depression at the lower part of the 

 urinary sac; the terminal papillae of the ureters 

 are situated with the orifices of the genital 

 ducts, in the same segment of the cloaca, 

 which is therefore termed the urethro-sexual 

 cavity (e, fig. 176). 



The space intervening between the urethro- 

 sexual cavity and the valvular termination of 

 the rectum (c,fg. 176) forms a cavity more or 

 less developed in different birds, but always 

 distinct in the smoothness of its lining mem- 

 brane from the rectum, which has a more vas- 

 cular and villous internal tunic. The birds in 

 which this rudimental urinary bladder presents 

 the largest capacity are the Owls, many of the 

 aquatic birds, as the Pelecan, Willock, Grebe, 

 Swan, &c. ; some of the Wading Order, as the 



Bittern and Bustard, but more especially the 

 Ostrich, among the Cursorcs, in which the 

 urinary receptacle is represented as laid open 



Fig. 176. 



A 



Oken's Isis, 1826, p. 414. 



Cloaca of the Ostrich.'* 



The Supra-renal Glands, Renal capsules, 

 Glandule succenturiata (d, d, Jig. 182) are 

 small bodies, usually of a bright yellow colour, 

 situated on the mesial or inner side of the su- 

 perior extremities of the kidneys; closely at- 

 tached to the coats of the contiguous large veins 

 and in contact with the testes in the male ; and 

 the left one adhering to the ovary in the female. 

 They vary in shape, being sometimes of a 

 round, flattened, oval, or irregularly triangular 

 figure. They are proportionally smaller than 

 in mammalia, being in the Goose each about 

 the size of a pea. 



They present, like the kidneys, a homoge- 

 neous texture throughout, and do not exhibit 

 the alternate strata of different-coloured sub- 

 stances as in mammalia. In the Gigantic Crane 

 we found the texture of the supra-renal glands 

 to be coarsely fibrous; in the Hornbill they 

 were granular, similar to the kidney; in the 

 Pelecan they were of a granular but more 

 pulpy texture. 



There is no cavity in the supra-renal glands. 

 The veins which return the blood from them 

 are of proportionally large size, as in all the 

 parenchymatous bodies without excretory ducts. 

 The supra-renal glands have been found to 

 present a slight enlargement corresponding with 

 the increased development of the sexual organs; 

 and it has been conjectured that their function 

 is related to that of the generative system. 



Thyroid Glands. In many birds, as the 

 Vultures, Falcons, Starling, Magpie, Heron, 

 Bustard, and in most Aquatic birds, two glands 

 are found, one on each side of the trachea, very 

 near the lower larynx and frequently attached 

 to the jugular veins. They are regarded as the 

 analogues of the thyroid glands. In addition 

 to these there are two small glands, in the Gan- 

 net, attached to the upper part of the commence- 

 ment of each bronchus. 



From Memoires du Museum, torn. xv. pi. 1,juj. 1. 



