288 



CLASS AMPHIBIA. 



part of the body ; the principal functional difference being that in 

 Amphibia the left subclavian is in connection with the left systemic arch, 

 whereas in Reptilia it conies off from the system of^the rightjarch. 



Four arterial arches are developed in the Amphibia, the first, 

 second, third and fourth branchial. In addition to the seethe 

 ventral aorta of the larva sends a branch to the hyoid which 

 however is usually incomplete, not reaching the dorsal system ; 

 in all cases it eventually atrophies. The vascular arches of the 

 larval salamander are shown in Fig. 161. The ventral aorta 

 gives off four branches on each side. Of these the first three 

 pass to the first three branchial arches and supply their gills. 

 They may consequently be described as consisting of an afferent 

 (branchial artery) and an efferent (branchial vein) portion united 



Fro. 162. Arterial arches of an adult Salamandra maculosa (after Boas). 1, 2, 3, 4 the four 

 branches of the ventral aorta (vascular arches) ; ao dorsal aorta ; aw root of dorsal aorta ; 

 cd carotid gland ; ce external carotid ; ci internal carotid ; co conus arteriosus ; cu ductus- 

 Botalli of pulmonary arch ; p pulmonary artery ; oe oesophageal branches of p ; S sub- 

 clavian artery ; tr ventral aorta. 



by the vessels in the gills. In addition to these connections 

 the afferent and efferent vessels of the second and third branchial 

 arches are directly connected by anastomosing vessels (y, z). 

 The first afferent vessel is not so connected with its branchial 

 vein, but fine anastomosing vessels (x) pass between it and the 

 external carotid (ce, lingual) which is a branch of the first efferent 

 vessel. Further dorsally the first efferent vessel gives off the 

 internal carotid (ci). All the efferent vessels fall into the dorsal 

 aorta. The fourth vascular arch is not connected with a gill ; 

 it is a slender vessel running in the fourth branchial arch. Dor- 

 sally it gives off the pulmonary artery and joins the efferent 

 vessel of the third arch ; of which indeed the pulmonary artery 

 has the appearance of being a branch. 



