130 Edward Phelps Allis jr., 



works seeming to indicate that the mandibulo-internal is usually 

 somewhat dominant. 



In adult dipnoids, if Cei-atodus can be taken as a type for the 

 order, and in Torpedo, there is a strictly hyo-internal type. 



In adult holostean ganoids the glosso-internal type is strongly 

 dominant but not absolute. 



In adult teleosts the glosso-internal type is absolute. 



In amphibians and higher vertebrates, the type is also a glosso- 

 internal one, but here specialization is carried further by the abortion 

 of the dorsal aortic connection between the glossopharyngeal and 

 first vagus aortic arches. 



The external carotid artery, so-called, is sometimes a dorsal 

 and sometimes a ventral artery. 



The dorsal external carotid would seem to be an artery 

 developed from the dorsal nutritive or muscle branches of one or 

 more prevagal aortic arches, and in all fishes excepting only dipnoids 

 (Ceratodus), the principal component of the artery would seem to be 

 derived from the hyoidean arch. In Ceratodus it is derived from the 

 glossopharyngeal arch. The artery may send branches into the cranial 

 cavity, such a branch in the Loricati being said to be distributed to 

 the adipose tissues, only, in that cavity. It is possible, or even 

 probable, that this artery contains ventral remnants of certain 

 premandibular aortic arches, and it is certain that it tends to become 

 connected, by commissure, with ventral portions of the mandibular 

 and hyoidean aortic arches. When this latter connection is 

 established, the blood current through the carotid supplements, either 

 directly or indirectly, the afferent current in the mandibular aortic arch. 



A ventral external carotid is found, as such, in amphibians, but 

 not in fishes or in the Sauropsida. In amphibians it takes its origin 

 either from ventral or intermediate portions of the glossopharyngeal 

 aortic arch, and is said to be developed trom ventral remnants of 

 the mandibular and hyoidean aortic arches. In this condition it 

 seems to simply represent the ventral portions of those two aortic 

 arches of fishes; the hyoidean, mandibular, and premandibular 

 (choroid) gills, and related portions of the aortic arches, being wholly 

 suppressed. But, in further development (in the chick), this ventral 

 carotid becomes connected with the dorsal external carotid — as do 

 the corresponding arteries in teleosts and Amia — and the con- 

 nection with the glossopharyngeal aortic arch then aborting, the 

 artery becomes, in appearance, a branch of the dorsal artery. 



