84 ANATOMY OF THE RABBIT. 
termination, the vermiform process, being dorsal in position and 
directed for the most part backward. 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 and left colic arteries, comparable to those 
of man; while on the other hand the right colic relation, on account 

Fic. 44. The heart and lungs from the ventral surface: ad, 
right atrium; ao, aorta; ap, pulmonary artery; as, left atrium; 
d, right superior caval vein; i’, i’, left and right inferior lobes 
of lung; 1, aortic ligament; m’, m’’, middle lobes; ml, medial 
lobule of right inferior lobe; s’, s’’, superior lobes; tr, trachea; 2 
vd, right ventricle; vp, pulmonary veins; vs, left ventricle. 
of the great complexity of its parts, is represented by a large» 
number of vessels, branches of a common ileocaecocolic trunk. 
THE RESPIRATORY SYSTEM. 
In all air-breathing vertebrates the lungs (Fig. 44) are paired 
sacs which arise embryonically as ventral outgrowths of the digestive 
tube, and are secondarily connected with the outside of the body 
