140 



facialis branch of the external carotid of Polyodon, Acipenser and 

 certain teleosts, which, in teleosts, also traverses the facialis canal 

 through the hyomandibular, must then also be a persisting remnant of 

 the posterior efferent hyoidean artery. 



This then would account, in Araia and teleosts, for all the vessels 

 here found in selachians excepting only the external carotid, the dorsal 

 commissure that connects the efferent hyoidean and first branchial 

 arteries and the intermediate commissure that connects the hyoidean 

 and mandibular arteries and that becomes, in selachians, the secondary 

 afferent pseudobranchial artery. This latter artery, which is found in 

 normal position and function in the adults of both Acipenser and 

 Lepidosteus (see Allis 1908a), is represented in Amia and teleosts, 

 as Maurer (1888, p. 215) has shown, in a branch or branches given 

 off by the afferent mandibular artery just before that artery perforates 

 the suspensorial apparatus, or while it is traversing the external surface 

 of that apparatus, the branch or branches being distributed to the tissues 

 at the dorsal end of the ceratohyal or to those in the opercular 

 region ; while the dorsal commissure between the efferent hyoidean 

 and first branchial arteries is apparently represented, in Amia and 

 teleosts, in a branch sent by the hyo-opercularis of the one or the 

 facialis branch of the external carotid of the others to muscles at 

 the dorsal end of the hyoidean arch. 



The hyo-opercularis artery of Amia and the facialis branch of the 

 external carotid of teleosts thus become, in origin and distribution, 

 apparent serial homologues of the dorsal branchial muscle artery of 

 Amia, and this strongly suggests that the external carotid, which 

 appears as a dorsal branch of the efferent hyoidean artery in certain 

 selachians, must be a similar artery. If it be such an artery, it must 

 have been developed in relation to prehyoidean efferent arteries and 

 dorsal commissures, and possibly also in part from the anterior ef- 

 ferent hyoidean artery, which artery is otherwise not accounted for. 

 This method of development would then account for the differing 

 points of origin of the external carotid in the different orders 

 of fishes, its different connections in ganoids and teleosts with the 

 hyo-opercularis (efferent hyoidean) artery, and the commissural 

 connection (secondary afferent pseudobranchial artery), in certain 

 ganoids and teleosts, with the mandibular pseudobranch. For, if 

 the latter commissural vessel (secondary afferent pseudobranchial 

 artery) were, in such a fish as Amia, to be split off from the 

 carotid and acquire an independent origin from the lateral dorsal 



