638 COLLEGE ZOOLOGY 



The posterior continuation of the mouth cavity is called the 

 pharynx. In the floor of the pharynx is the respiratory opening, 

 the glottis, which is covered by a bilobed cartilaginous flap, 

 the epiglottis, during the act of swallowing. The pharynx leads 

 into the narrow, muscular (esophagus. Following this is the 

 stomach; then comes the U-shaped duodenum, into which the 

 pancreatic duct from the pancreas and the bile duct from 

 the liver open. 



The small intestine, which is seven or eight feet in length, leads 

 into the colon, which is continued as the rectum. At the an- 

 terior end of the colon a large, thin-walled tube, the cacum, is 

 given off. This caecum is about an inch in diameter and twenty 

 inches long; it ends in a thick- walled, finger-like process about 

 four inches long, called the vermiform appendix. A large caecum 

 is characteristic of most herbivorous animals with simple 

 stomachs. 



The rabbit possesses the following ductless glands : the spleen, 

 the thymus, the thyroid, and the suprarenals. 



THE CIRCULATORY SYSTEM. The blood corpuscles of the 

 rabbit are unlike those of the lower vertebrates, being smaller, 

 round instead of oval, biconcave, and without nuclei. The 

 heart is four chambered, as in the pigeon, but the main blood- 

 vessel, the aorta, arising from the left ventricle, has only the left 

 arch, whereas in birds the right arch persists. The right sys- 

 temic arch of the rabbit is represented by the innominate artery, 

 which is the common trunk of the right carotid and subclavian 

 arteries. An hepatic-portal system is present, but no renal-portal 

 system. 



The lymphatic system is important in rabbits and other mam- 

 mals. The fluid portion of the blood, which, because of the 

 blood pressure, escapes through the walls of the capillaries into 

 the spaces among the tissues, is collected into lymph vessels. 

 These vessels pass through so-called lymph glands, and finally 

 empty into the large veins in the neck. The lymphatics 

 which collect nutriment from the intestine are called lacteals. 



