CLASS AMPHIBIA 



485 



in the spleen, a gland in which worn-out red corpuscles are 

 destroyed. 



The heart (Fig. 413 b, Fig. 414) is the central pumping station 

 of the circulatory system. It is composed of a conical, muscular 

 ventricle (Fig. 413 b, 1), two thin- walled .auricles, one on the right 

 (2), the other on the left (3), a thick- walled tube, the truncus 

 arteriosus (4), which arises from the base of the ventricle, and a 



Fig. 413 b. — Heart of the frog. A, ventral view. B, dorsal view. C, ven- 

 tral wall removed. /, ventricle; 2, rigHt auricle; J, left auricle; 4, truncus 

 arteriosus; 5, carotid arch; 6, lingual artery; 7, carotid gland; S, carotid 

 artery; 9, systemic arch; 10, pulmocutaneous arch; if, innominate vein; 

 12, subclavian vein; 13, vena cava inferior; 14, vena cava superior; 15, opening 

 of sinus venosus into right auricle; 16, pulmonary vein; 17, aperture of entry 

 of pulmonary vein; iS, semi-lunar valves; iq, longitudinal valve; 20, point of 

 origin of pulmocutaneous arch. (From Shipley and MacBride, after Howes.) 



thin- walled, triangular sac, the sinus venosus (Fig. 413 b, B), on 

 the dorsal side. 



The arteries (Fig. 414) carry blood away from the heart. The 

 truncus arteriosus (Fig. 413 b, 4; Fig. 414, tr.a) divides as shown 

 in Figure 413, A, and each branch gives rise to three arteries. 



(1) The common carotid (Fig. 413 b, A, 5; Fig. 414, c.c) divides 

 into the lingual or external carotid (Fig. 414, I), which supplies 

 the tongue and neighboring parts, and the internal carotid, which 

 gives off the palatine artery to the roof of the mouth, the cerebral 



