VASCULAR SYSTEM. 379 



generally larger than the others. The tongue is flat and not 

 protrusible. Salivary glands are absent. There is a transverse 

 fold of the mucous membrane of the palate just in front of 

 the choanae, which can shut off the mouth from the pharynx. 

 The stomach is a gizzard-like sac, with muscular walls and 

 tendinous discs. The pylorus is near the oesophageal opening. 

 There is a gall bladder, but no caecum. 



The cloaca is divided into two parts by a muscular fold. Into 

 the anterior chamber open the urinary and generative ducts by 

 separate and paired openings. There is no bladder. On the 

 ventral side of the posterior chamber of the cloaca is a grooved 

 penis * very similar to that of the Chelonia (p. 410). Peritoneal 

 canals are present in both sexes and open on either side into the 

 cloaca at the base of this organ. 



The testes are oval, the kidneys lobed, and the ovaries elon- 

 gated. 



The trachea is long and provided with complete rings. There 

 is a larynx with vocal chords. The epiglottis is absent, and the 

 larynx has an annular cartilage corresponding to the cricoid and 

 thyroid of higher forms, and arytenoid cartilages. The lungs 

 hang freely in the body cavity and are well developed and spongy. 

 The bronchus enters at about the middle of the organ and is 

 continued to its hind end ; it soon loses its rings, and is beset 

 with openings which lead into pouches, the walls of which are 

 honeycombed. 



The lungs lie in the anterior horns of the body-cavity. These 

 are partitioned off from the rest by a septum t which is partly 

 muscular and partly membranous and has peculiar relations to 

 the liver and stomach. It is analogous but not homologous to 

 the mammalian diaphragm and is said to assist in the inspira- 

 tory movements. 



Vascular system. The sinus venosus is closely applied to 

 the heart and receives the three great systemic veins. The 

 ventricle is double. The right aortic arch proceeds from the left 

 ventricle and gives off the arteries to the head and anterior 

 limbs. These are an innominate and a right subclavian ; the 

 innominate divides into left subclavian and carotis primaria 

 which divides into the two common carotids. The left aortic 



* Boas, Gadow op. cit. 



t G. W. Butler, P.Z.S., 1889, p. 452. 



