462 



ZOOLOGY 



SECT. 



sem.1/ 



marked by a spiral constriction, indicating the presence in its 

 interior of a narrow spiral valve. At its extremity is a small, 

 fleshy, finger-like vermiform api^endvx. 



The intestine, like that of the Pireon, is attached tlirousfhout 

 its length to the dorsal wall of the abdominal cavity by a mesentery, 

 or fold of the lining membrane or peritoneum. 



The liver is attached to the diaphragm by a fold of the peri- 

 toneum. Its substance is partly divided by a series of fissures 

 into five lobes. A thin-walled gall-bladder lies in a depression on 

 its posterior surface. The common hile-duct (c.h.d.), formed by 

 the union of cystic duct from the gall-bladder and hepatic ducts 

 from the various parts of the liver, runs to open into the duodenum 

 near the pylorus. 



The pancreas {pn.) is a diffused gland in the fold of mesentery 

 passing across the loop of the duodenum. Its single duct, the 

 pimcrcativ duct {'pn. d.), opens into the distal limb of the loop. 



Circulatory Organs. — The heart (Fig. 1090) is situated in 

 the cavity of the thorax, a little to the left of the middle line, 



and lies between the two 

 pleural sacs enclosing the 

 lungs. Between the pleural 

 sacs is a space, the media- 

 stinum (Fig. 1093). This 

 is divisible into four parts, 

 the anterior, the dorsal, 

 the middle, and the ven- 

 tral. In the anterior part 

 lie the posterior part of 

 the trachea, the nei^h- 

 bouring parts of the oe-so- 

 phagus and of the thoracic 

 duct of the lymphatic 

 system, the roots of the 

 great arteries and the veins 

 of the pre-caval system, 

 and the phrenic, pneumo- 

 gastric, and other nerves. 

 In the dorsal part are 

 situated the posterior part 

 of the oesophagus, the thoracic part of the dorsal aorta, the 

 pneumogastric nerve, the azygos vein^ and the thoracic duct. 

 The middle part is the widest, and lodges the heart and roots 

 of the aorta and pulmonary artery enclosed in the pericardium, 

 the posterior portion of the pre-caval veins, the phrenic nerves, 

 the terminal part of the azygos vein, and the roots of the 

 lungs. The ventral part contains only areolar tissue with 

 the thymus gland. The pericardial membrane enclosing the 



=r/7/. 



pa^ 



Fig. 1090.— Lepus cuniculus. Heart, seen from 

 the right side, tlie walls of the right auricle and 

 right ventricle partly renuived so as to expose the 

 cavities, ao. fioi-ta ; ./. ov. fossa ovalis ; I. pr. <■. open- 

 ing of left i^recaval ; m. pap. musculi papillares ; 

 pt c. postcaval ; pt. c'. opening of postcaval ; r.pr.c. 

 right precaval ; r. pul. right pulmonary artery ; 

 sem. V. scmihuiar valves ; tri. v. tricuspid valve. 



