112 EDWARD PHELPS ALLIS, JR. 



present identified, the dorsal connection of this latter artery and 

 the arteria mandibularis with the hyo-mandibular cross-com- 

 missure, and the prolongation of this latter commissure, ante- 

 riorly, to fall into the mandibular branch of the carotis externa 

 were not then found and are not shown. In Mustelus and Hep- 

 tanchus I now also find these several arteries in what would seem 

 to be strictly equivalent conditions, but as the dissections of 

 these fishes were not made primarily to determine the minor 

 arterial connections, certain of the commissural vessels were not 

 found. The afferent mandibular artery, in both Mustelus and 

 Heptanchus, is also a much less important vessel than in Chlamy- 

 doselachus, and there are apparently also certain minor differ- 

 ences in the distribution of the arteries. It is however certain, 

 from the conditions found in these three fishes, that the so-called 

 mandibular artery, or arteria mandibularis, of current descrip- 

 tions of the adult selachian is not the persisting mandibular 

 aortic arch, which it is primarily the purpose of this investi- 

 gation to establish, and the relations of this artery to the cerato- 

 hyal, to the nervus mandibularis internus facialis, and to the 

 muscles of the region all indicate that it is, as already stated, 

 the anterior efferent artery of the hyal arch. 



This anterior efferent hyal artery must then be developed, in 

 stages later than those examined by Dohrn, from the lacunae 

 said by that author to be distributed along the anterior surface 

 of the hyal arch of embryos, the primitive aortic vessel of the 

 mandibular arch then diminishing in relative size, or, as is said 

 to be the case in Torpedo, completely aborting. That this ante- 

 rior efferent hyal artery should develop later than the posterior 

 one, is wholly in accord with Raffaele's statement, above referred 

 to, that the anterior efferent arteries of the branchial arches 

 develop later than the posterior ones; and, as this anterior efferent 

 hyal artery must primarily have fallen into the cross-commissural 

 vessel from the hyal to the mandibular arches, and as both it and 

 the artery that I have here considered to be the afferent man- 

 dibular artery carry aerated blood to the spiracular gill, there 

 would seem to be nothing singular in the fact that, in Chlamy- 

 doselachus, they have coalesced in their dorsal portions and there 



