116 Edward Phelps Allis jr., 



Posterior to its three terminal branches, and while transversing 

 what is either the extreme hind end of the orbit or the anterior 

 end of the myodome, the internal carotid, both in old larvae and 

 in the adult, is connected by a small vessel with the large so-called 

 efferent pseudobranchial artery, this small vessel being* always de- 

 scribed as a commissural connection between the two large arteries. 

 This so-called commissural vessel, so relatively unimportant in the 

 iidult, is however the greatly reduced dorsal end of the mandibular 

 aortic arch, as my figures of young stages make evident, and it 

 and that portion of the so-called efferent pseudobranchial artery 

 that lies proximal to it, together form the homologue of the anterior 

 ■carotid of selachians. That portion of the so-called efferent pseudo- 

 branchial artery that lies distal to the commissure, although 

 appearing as the direct and main continuation of the artery, is 

 then simply a branch of the true efferent artery, and it alone is 

 the homologue of the arteria ophthalmica magna of selachians. 



The next posterior branch of the internal carotid is a small 

 branch sent forward in the palatine canal as the main artery turns 

 upward to leave that canal and pierce the overlying cartilage of 

 the basis cranii. If this overlying cartilage were to be resorbed, 

 as it is in the Loricati, this small artery would have an origin from 

 the internal carotid greatly resembling that of the orbito-nasal artery 

 of Allen's (1905) descriptions of the latter fishes; but its forward 

 course in the palatine canal, without entering the orbit, would seem 

 to indicate that it can, at most, only represent a portion of the 

 latter artery. Moreover, this artery of Aniia runs forward mesial to 

 the ophthalmica magna, instead of lateral to that artery, as the 

 orbita-nasal of teleosts does. 



The next posterior branch of the lateral aortic trunk, here 

 called the common carotid, is the external carotid artery. The 

 full course of this artery I did not trace, but it runs forward and 

 downward and is doubtless distributed to palato-quadrate and pre- 

 mandibular regions, as it is said to be in teleosts. It is an artery 

 that apparent]}^ develops in somewhat late embryonic stages, for it 

 is not shown in my figures of 6 mm and 7 mm embryos; and even 

 in my figure of a 9 mm embryo it is shown as a small and un- 

 important branch that apparently was not at the time considered 

 of any especial importance. In all the earlier stages in which it is 

 found, it does not have anj^ apparent connection with the pseudo- 

 branch, but in later stages it acquires such a connection; and, 



