104 



ANATOMY OF THE RABBIT 



It may be observed at this point that in their vascular supply the 

 more typical divisions, namely, the transverse and descending- 

 colons, have arterial branches, respectively, the middle ana left 

 colic arteries, comparable to those of man : while on the other hand 

 the supply to the parts on the right side, the ascending colon, 

 caecum, and related portions, on account of their great elaboration, 



is represented by a large number of 



^'k " ^. vessels, branches of a common ileo- 



h1 :tf "^^ caecocoHc trunk. Each of these vessels 



B 1 ^■BI^^^L. anastomoses with its immediate 



m^P § ^Hjil^^m neighbours so that the large intestine 



'•■^^ ^^^^^^m is supplied by a continuous series 



^(F '^m^t^^ ^^ arterial loops from which smaller 



branches are distributed to the in- 

 testinal walls. 



The elaborations of the ascending- 

 colon and of the caecum, which 

 contrast markedly with conditions in 

 carnivorous mammals, (figs. 54, 56), 

 are highly instructive examples of 

 adaptation to the character of the 

 diet. 



Fig. 56. Caeca of a cat and of a 

 man, dorsal view. The former 

 short, without a vermiform process, 

 connecting with a smooth colon. 

 The latter cup-like, with a vermi- 

 form process proportionally smaller 

 than that of a rabbit, and having 

 bands and haustra continuing those 

 of the colon. 



The Respiratory System 

 In all air-breathing vertebrates, the lungs (Fig. 57) are paired 

 sacs which arise embryonically as ventral outgrowths of the diges- 

 tive tube, and are secondarily connected with the outside of the 

 body through special perforations of the anterior portion of the 

 head and through the oral cavity. The principal connection in a 

 mammal is represented by an extensive nasal cavity bearing on its 

 lateral walls the olfactory sense-organs. It is distinguished as an 

 accessory respiratory tract from the true respiratory tract formed 

 by the trachea and its terminal divisions, the bronchi. The respira- 

 tory system, as represented by the lungs and related tubes, being 

 developed as a ventral outgrowth of the pharynx, is nominally 

 ventral to the oesophagus, but in the adult animal this relation is 

 actually true chiefly of the trachea. In the thorax (Plate VH) 

 the bronchi are, in general, interposed between the oesophagus and 



