Pseudobranchial and Carotid Arteries in the Gnathostome Fishe>;. 119 



thick, and while the connection with the orbito-nasal was evident, 

 that with tlie ophthalmica magna could not be positively established. 

 Exactly similar conditions are found in Scomber, the only other 

 teleost I have examined in this connection. In an earlier work. I 

 stated (1903, p. 93) that in the adult of that fish the internal 

 carotid receives a delicate communicating- branch from the ophthal- 

 mica magna. My present work leading me to think this exceptional 

 in the specimen examined, if not in error, I have examined the 

 vessels in a single series of sections that I have of one half of the 

 head of a small but adult Scomber, and I find the conditions exactly 

 similar to those in the Loricati. A small branch is sent from the 

 orbito-nasal artery to the ophthalmica magna, and pierces the 

 membranous sheath of the latter artery; the connection being so 

 intimate that even in sections the branch might be considered as 

 a communicating one, had one not been specially put on guard 

 against such an interpretation of the relations. 



The conditions, both in Scomber, and in the Loricati, would thus 

 seem to indicate that the orbito-nasal was originally connected by 

 commissure, or by anastomosis, with the ophthalmica magna, and 

 that it is actually shown in process of separation from that artery. 

 If this be so, some basal portion of the orbito-nasal must represent 

 that dorsal portion of the mandibular aortic arch that lies between 

 the ophthalmica magna and the internal carotid. The remaining, 

 distal portion of the orbito-nasal would then either represent a 

 dorsal nutritive, or muscle branch of the same aortic arch, similar 

 to those already referred to on more posterior arches, or simply be 

 a specially developed prolongation of the dorsal remnant of the 

 arch, after that remnant had been pinched off from the ophthalmica 

 magna. The orbito-nasal of teleosts, it is to be noted, while it 

 appears to replace functionally, in those fishes, a part of the external 

 ■carotid of elasmobranchs, can not well be a detached branch or 

 portion of that artery; its course through the myodome apparently 

 forbidding this. And an independent orbito-nasal artery, or anything 

 resembling it, I do not find described either in elasmobranchs or in 

 ganoids, unless those small branches of the internal carotid that 

 traverse the palatine canal in Amia and Lepidosteus represent the 

 artery; which, as already stated for Amia, seems improbable. 



DoHEN (1886) assigns a totally different fate to the dorsal 

 portion of the mandibular aortic arch. He first says that this por- 

 tion of the arch, the part that lies between the ophthalmica magna 



