16 Descriptions of Preparations. 



reaches backwards so far as to interpose itself for some distance 

 between the anterior lobe of the kidney and the os ilii. It differs 

 from the Mammalian lung" also in being lodg-ed conformably to 

 the intercostal spaces, and being indented by the six unanchylosed 

 ribs, instead of being freely suspended, as is invariably the case 

 in mammals, and divided into lobes, as is very ordinarily the case 

 in those animals. Another and most important point of difference 

 is furnished by the prolongation of the lung, by means of its bron- 

 chial stem and branches, into air-cells ™ permeating a very large 

 part of the entire body. The largest of these receptacles are the 

 infrarenally-placed ' abdominal air sacs/ the right one of which, 

 presenting an appearance like that of the Mammalian omentum, 

 is seen extending from the posterior border of the lung above and 

 behind the liver, so as, firstly, to interpose itself between the inferior 

 surface of the kidney and the intestines, and, secondly, to stretch 

 beyond the region of the kidney into that of the rectum. The 

 kidney, like the lung, is indented by the bones it is in relation 

 with ; and it is divisible here into three lobes, increasing in size 

 from before backwards conformably with the iliac and pelvic fossa. 

 There are no specialized renal arteries in birds as there are in 

 mammals, but we see some branches passing to the organ from 

 the ischiadic artery in the interval between the middle and posterior 

 lobe, whilst one of the chief factors of their short vena cava inferior 

 is seen in the interval between the middle and the anterior lobes. 



In all birds, and in no other class of animals, will the same 

 description as that given here apply to the nerve-system, and the 

 relations of the muscles of the anterior limb, and to the relations 

 of the aorta to the right bronchus. The peculiarities of the pan- 

 creas and duodenum are probably nearly equally distinctive. The 

 crop and the uropygial gland are peculiar to, though not universally 

 found in Birds. 



m For an account of the air sacs, see Milne-Edwards, 'Lemons,' ii. 351, and for the 

 relations of the air sacs shown in this preparation, see Natalis Guillot, ' Ann. Sci. 

 Nat.' 1846, series iii. torn. v. p. 60 ; and for figure, C. G. Carus, 1. c. pars. vi. 

 tab. vii. 



