VASCULAR SYSTEM 311 



is no time for its contained blood to get thoroughly mixed before it 

 is forced into the conus. 



As in the Dipnoi, four afferent branchial arteries (Fig. 250) 

 arise on either side from the short conus in the Amphibia, which 

 taking as a type the larva of Salamandra have the follow- 

 ing relations (comp. Fig. 243, c). 



The three anterior arteries pass to numerous external gill-tufts, 

 in which they break up into capillaries (Fig. 251). 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 



FIG. 251. THE ARTERIAL ARCHES OF THE LARVA OF A SALAMANDER. (Slightly 

 diagrammatic.) (After J. E. V. Boas.) 



tr, truncus arteriosus ; 1 to 3, the three afferent branchial arteries ; / to ///, the 

 corresponding efferent arteries ; 4, the fourth arterial arch, which becomes 

 connected with the pulmonary artery (Ap) ; a, a, direct anastomoses between 

 the second and third afferent and efferent branchial arteries ; re, external 

 carotid ; ci, internal carotid ; f, net-like anastomoses between the external 

 carotid and the first afferent branchial artery, which give rise later to the 

 " carotid gland" ; RA, aortic roots ; Ao, dorsal aorta. The arrows show the 

 course which the blood takes. 



branchial artery, which is smaller than the others, does not pass to 

 a gill, but to the pulmonary artery, which arises from the third 

 efferent branchial. The pulmonary artery, therefore, contains far 

 more arterial than venous blood, and thus the lungs of the Sala- 

 mander larva, like the air-bladder of Fishes, can only be of 

 secondary importance in respiration. 



The internal carotid arises from the first afferent branchial 

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

 further outwards (Fig. 251). The latter, as it passes forwards, 

 becomes connected with the first afferent branchial by net-like anas- 

 tomoses, and these give rise later to the so-called " carotid gland" l 



1 The " carotid gland " loses its character as a refe mirabile (comp. p. 333), 

 and in the adult consists simply of a muscular vesicle with septa in its interior. 



