104 EDWARD PHELPS ALLIS, JR. 



cult to reconcile Dohrn's account of the origin of the thyro-mandibular 

 artei'y with the conditions in the stage of Mustelus above described. 

 It is difficult to conceive an aortic arch losing its connection with the 

 truncus arteriosus, and becoming connected with the efferent vessel 

 of the second arch behind it. 



From the above quotations it would seem that Wright con- 

 sidered the artery described by him in Mustelus to be not only 

 the homologue of the arteria hyoidea of Lepidosteus and the 

 Teleostei, but also to be identical with the arteria thyreo-mandib- 

 ularis described by Dohrn in other selachian embryos, and that, 

 rather than question this identity, he was inclined to doubt the 

 origin of the artery, as described by Dohrn, from the afferent 

 hyal artery. Dohrn however later ('86, pp. 166-168) found that 

 the maridibular aortic arch of trout embryos, which he identifies 

 as the so-called arteria hyoidea of the adult teleost, has its point 

 of origin secondarily transferred from the truncus arteriosus to 

 the ventral end of the efferent artery of the first branchial arch, 

 these two connections, in certain embryos, even both existing, 

 cotemporaneously, before the one with the truncus arteriosus 

 definitely aborts. The so-called arteria hyoidea of teleosts he 

 identifies as the homologue of the arteria thyreo-mandibularis 

 of his own descriptions of selachian embryos, and, as he par- 

 ticularly discusses Wright's work above referred to and says 

 nothing to the contrary, he certainly considered the artery 

 described by that author in Mustelus to be identical with the 

 arteria thyreo-mandibularis of his own descriptions. 



In the adult selachian, the earliest descriptions that I can 

 find of the artery here under consideration, in the works at my 

 disposal, is that by Parker ('86) of Mustelus antarcticus. In 

 Balfour's ('81) still earlier works a mandibular artery is frequently 

 referred to, but the references would seem to be to the artery in 

 embryos only. Parker (1. c), who evidently had not seen either 

 of the works by Dohrn and Wright to which I have above re- 

 ferred, says that the 'mandibular artery' of Mustelus antarcticus 

 arises from the ventral end of the 'first efferent branchial artery,' 

 the efferent artery thus referred to being the posterior efferent 

 artery of the hyal arch. The mandibular artery is then said to 



