MANDIBULAR ARTERY AORTIC ARCH-. 115 



corresponding edge of the anterior upper labial, both branches 

 suggesting efferent arteries of a premandibular arch. 



A further fact that is in favor of the origin of the carotis externa 

 from the dorsal lateral commissure is the course of the carotis 

 through the trigemino-facialis chamber in the Holostei and in 

 many of the Teleostei. This course of this artery has always 

 been to me one of the puzzling facts in the cranial anatomy of 

 fishes. But if that part of the artery which traverses the tri- 

 gemino-facialis chamber represent a part of the dorsal lateral 

 commissure, and the lateral wall of the trigemino-facialis cham- 

 ber be derived from the extrabranchial of the mandibular arch, 

 as I have latelj^ sought to establish (Allis, '15), this course of the 

 artery is wholly natural; for in Lamna, the one remaining speci- 

 men of an adult selachian that I have which is suitable for this 

 purpose, and which I have just re-examined, I find that the at- 

 tachment of the extrabranchial of the first branchial arch to the 

 inner cartilages of that arch is lateral to the dorsal lateral com- 

 missure of the efferent arteries. When the extrabranchial and 

 pharyngobranchial of the mandibular arch fused with the neuro- 

 cranium to form, respectively, the lateral wall and the floor of 

 the trigemino-facialis chamber, the dorsal lateral commissure 

 naturally became enclosed in the chamber so formed. And 

 this is, conversely, a further fact in favor of my conclusion that 

 these elements of the mandibular arch have been used to form 

 the walls of the chamber. 



The artery sent, in Chlamydoselachus, from the anterior 

 efferent hyal artery to the inner surface of the gape was not found 

 in either Mustelus or Heptanchus, but this does not necessarily 

 mean that it does not there exist, for, as already stated, the 

 dissections of these two fishes were not primarily made with 

 reference to a study of all the arteries of the region. What the 

 significance of this artery is could not be determined, but it is 

 to be noted that, like the nervus mandibularis internus facialis, 

 it is a structure of hyal origin distributed to the inner surface 

 of the mandibular arch, and it apparently has some definite 

 relation to the little pocket in the lining membrane of the mouth 

 cavity. In my work on Polyodon, I found (Allis, '11a, p. 286), 



