114 EDWARD PHELPS ALLIS, JR. 



were to abort, so separating the dorsal and ventral portions of 

 the carotis from each other, the conditions described by Parker 

 in Mustclus antarcticus would arise, the dorsal portion of the 

 carotis becoming the buccal artery of that author's descriptions 

 and the ventral portion becoming the strictly mandibular part 

 of the mandibular artery of that fish. If, on the contrary, the 

 cross-commissural vessel of Chlamydoselachus were to abort, 

 the artery distributed to the mandible would become wholly a 

 terminal portion of the carotis externa, as I have shown it in 

 my earlier figures and descriptions of this fish. The origin, in 

 embryos, of the mandibular branch of the mandibular aortic 

 arch from the extreme dorsal end of the arteria thyreo-mandib- 

 ularis, so particularly and carefully described by Dohrn, would 

 then receive full explanation, and the continuous carotid vessel of 

 Chlamydoselachus would seem to be the anterior efferent artery 

 of the mandibular arch, its intimate association with the nervus 

 mandibularis trigemini seeming to preclude its being a pre- 

 Ikiandibular artery. If it be the anterior efferent mandibular 

 artery, the secondary connection, in Amia (Allis, '12 a), of its 

 dorsal portion with the mandibular pseudobranch is fully ex- 

 plained, and the several forms of secondary afferent pseudobran- 

 chial arteries found in the Teleostei could be readily derived from 

 it. The ventral portion of the artery would, accordingly as it 

 retained its connection with the dorsal portion or with the 

 afferent mandibular artery, give rise to the variations found 

 (or at least described) in these latter fishes in the artery dis- 

 tributed to the mandible. 



The conditions thus found and thus interpreted in selachians 

 favor the suggestion (Allis, '08 a, p. 107) that the carotis externa 

 is developed in connection with the prehyal portion of the dorsal 

 lateral longitudinal commissure of the efferent branchial arteries, 

 and also that its mandibular branch is formed by the anterior 

 efferent artery of the mandibular arch. The maxillary branch 

 of the carotis would then be the anterior continuation of the 

 dorsal lateral commissure, and from this artery, in Chlamydo- 

 selachus, a branch is sent ventro-posteriorly along the dorsal edge 

 of the posterior upper labip.1 cartilage, and another toward the 



