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, /), two thin- walled auricles, one on the right 

 (2), the other on the left (j), 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; .', right auricle; 3, left auricle; 4, truncus 

 arteriosus; 5, carotid arch; 6, lingual artery; 7, carotid gland; 8, carotid 

 artery; g, systemic arch; 10, pulmocutaneous arch; //, innominate vein; 

 /.?, subclavian vein; 13, vena cava inferior; 14, vena cava superior; ij, opening 

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

 of pulmonary vein; 18, semi-lunar valves; ig, 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. 



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

 into the lingual or external carotid (Fig. 414, /), 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 



