SECT, xin PHYLUM CHORDATA 433 



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 appendix. 



The intestine, like that of the Pigeon, is attached throughout 

 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 bile-duct (c. b. 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 

 pancreatic duct (pn. d.), opens into the distal limb of the loop. 



Circulatory Organs.- -The heart (Fig. 1027) 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 mediastinum (Fig. 1030). 

 This is divisible into four parts, the anterior, the dorsal, the 

 middle, and the ventral. In the anterior part lie the posterior 

 part of the trachea, the neighbouring part of the oesophagus 

 and thoracic duct, the roots of the great arteries, and the 

 veins of the pre-caval system, the thymus gland, and the phrenic, 

 pneumogastric, 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 lymphatic glands. The pericardial membrane enclosing the 

 heart consists of two layers, a parietal, forming the wall of the 

 pericardial cavity, and a visceral, immediately investing the heart. 

 Between the two is a narrow cavity containing a little fluid the 

 pericardial fluid. In general shape the heart resembles the heart 

 of the Pigeon, with the apex directed backwards and slightly to the 

 left, and the base forwards. Like that of the Pigeon, it contains 

 right and left auricles and right and left ventricles, the right and left 

 sides of the heart having their cavities completely separated off from 

 one another by inter-auricular and inter-ventricular partitions. 



Into the right auricle open three large veins the right and left 

 pre-caval veins and the single post-caval the first into the anterior 

 part, the second into the left-hand side of the posterior portion, 

 and the third into the dorsal surface. Projecting forwards from it 



VOL. II F F 



