131 



arteries a large trunk has its origin, on either side, from the truncus 

 arteriosus, this trunk immediately separating into two parts one of 

 which is the afferent artery of the second branchial arch and the 

 other the common trunk of the afferent arteries of the third and 

 fourth arches. 



The four efferent branchial arteries are all double at their ventral 

 ends; but in the first arch these two terminal branches reunite ven- 

 trally to form a single vessel, and from the ventral end of this single 

 vessel a ventral longitudinal commissure has its origin, this commissure 

 extending both anteriorly and posteriorly from the first branchial arch. 

 From the anterior, or prebranchial portion of the commissure a small 

 branch is first sent upward in the hyoidean arch, and then the 

 secondary afferent hyoidean artery is sent upward in that same arch, 

 the commissure beyond that point becoming the afferent mandibular 

 artery, which has the course and distribution given in my earlier works 

 (Allis, 1900 and 1908 a). The posterior, or branchial portion of the 

 longitudinal commissure runs backward internal to the afferent 

 branchial arteries and latero-dorsal to the truncus arteriosus, and 

 receives a communicating branch from each of the three succeeding 

 efferent branchial arteries. It then continues onward posterior to 

 the fourth branchial arch, but was not further traced. The communi- 

 cating branches received from the second, third and fourth efferent 

 arteries each lies in the anterior portion of its arch, and each arises 

 from its respective artery dorsal to the point where that artery 

 separates into its two ventral portions. Each branch is smaller than 

 the artery from which it arises, but, nevertheless, is seems evident 

 that the branch must represent the true ventral end of the artery of 

 its arch, whether the artery be primarily a single efferent artery in 

 its arch, or either an anterior or a posterior efferent artery. 



In elasmobranchs (see Allis 1908 a), both anterior and posterior 

 efferent arteries are developed in the branchial arches, and in the 

 adults of Mustelus, Torpedo and Raja it is the anterior artery, alone, 

 that retains its connection with the dorsal, so-called epibranchial 

 portion of the primary artery, the posterior efferent artery in each arch 

 losing its connection with the epibranchial artery of its own arch and 

 becoming connected, through the dorsal longitudinal commissure, with 

 the next posterior epibranchial artery. Both arteries, in the adult 

 Mustelus, are in connection, at their ventral ends, wit& a ventral 

 longitudinal commissure. In Acipenser (Ostroumoff, 1907), as in elas- 



9» 



