HEART 



405 



(Fig. 306, B) ; for, owing to the" spongy nature of the ventricle, 

 there is no time for its contained blood to get thoroughly mixed 

 before it is forced into the conns. 1 



As in the Dipnoi, four afferent branchial arteries arise on 

 either side in the Amphibia, which taking as a type the larva 

 of Salamandra have the following relations (cr. Fig. 301, c). 

 The three anterior arteries pass to a similar number of 'ex- 

 ternal gill-tufts, in which they break up into capillaries (Fig. 308). 

 From the latter three efferent vessels arise, which pass to the 

 dorsal side, and there unite on either side to form the aortic root. 

 The fourth afferent branchial artery, which is smaller than the 

 others, does not pass to a gill, but to the pulmonary artery, which 



FIG. 308. THE ARTERIAL ARCHES OF THE LARVA OF A SALAMANDER. From 

 the ventral side. Slightly diagrammatic. (After J. E. V. Boas.) 



a,a, direct anastomoses between the second and third afferent and efferent 

 branchial arteries ; Ao, dorsal aorta ; <-e, external carotid ; <-i, internal 

 carotid ; It A, aortic roots ; /*'. truncus arteriosus ; 1 3, the three afferent 

 branchial arteries ; 7 777, the corresponding efferent arteries ; 4, the 

 fourth arterial arch, which becomes connected with the pulmonary artery 

 (Ap) ; t, net-like anastomoses between the external carotid and the first 

 afferent branchial artery, which gives rise later to the carotid labyrinth. The 

 arrows show the course which the blood takes. 



arises from the efferent branchials. The pulmonary artery, 

 therefore contains far more arterial than venous blood, and thus 

 the lungs of the Salamander larva, like the swim-bladder of Fishes, 

 can only be of secondary importance in respiration. 



The internal carotid arises from the first efferent branchial 

 artery, towards the middle line, the external carotid coming off 

 further outwards (Fig. 308). The latter, as it passes forwards, 

 becomes connected with the first afferent branchial by net-like 



1 Special vessels supplying the walls of the heart are apparent!}' wanting in 

 the case of many Fishes and of Amphibians. In Elasmobranchs, coroiinrt/ nrferies 

 arise from the hypobranchial artery and coronary veins open into the sinus 

 venosus or auricle ; similar vessels have also been described in certain Ganoids 

 and Teleosts. Coronary veins occur in Cryptobranchus japonicus. 



