515 



branches, described below, these vessels not being otherwise shown or 

 described by Ayers. 



The eiferent hyoidean artery which, as above described, has the 

 position in its arch of a posterior eti'erent vessel, is as shown by 

 Ayers up to the point where that author shows it connected by com- 

 missure (his anastomatic branch an) with the efferent artery of the 

 first branchial arch. Above and anterior to that point this artery and 

 the other vessels of the region, as I find them, are markedly ditferent 

 from those described by Ayers. When the efiferent hyoidean artery 

 reaches the dorsal end of the gill cleft between its own arch and the 

 first branchial arch it sends a large vessel forward and mesially and 

 itself curves slightly backward above the dorsal end of the cleft. It 

 there receives the commissure that connects it with the efferent artery 

 of the first branchial arch and, contracting abruptly to a much smaller 

 vessel, turns sharply forward mesially and downward, and, having 

 traversed a foramen in the projecting, shelf- like ventral edge of the 

 hind end of the chondrocranium, falls into the lateral dorsal aorta of 

 its side. This little vessel, which certainly forms the dorsal portion 

 of the eiferent hyoidean artery, was not found by Ayers, and even 

 in the first one of my two specimens dissected it was broken on each 

 side and lost, its two ends alone remaining. In the second specimen 

 dissected, where the vessel itself was larger, and where it was more 

 carefully looked for, it was found complete, as above described, on 

 each side. 



The large vessel above referred to, given ofi by the efferent 

 hyoidean artery just as it reaches the dorsal end of its cleft, runs 

 forward and mesially and falls into the lateral dorsal aorta of its side 

 at a sharp bend in that artery, this bend lying somewhat anterior to 

 the middle point between the point where the aorta is joined by the 

 dorsal end of the efferent hyoidean artery and the point of origin of 

 the external carotid. This large vessel is shown by Ayers and is in- 

 cluded in the common carotid and part of the internal carotid of his 

 descriptions; and as no other connection of the efferent hyoidean artery 

 with the dorsal aorta is given by Ayers, I considered this vessel, in 

 the diagram of the arteries of this fish given in my earlier work 

 (Allis, 1908), as the dorsal end of the efferent hyoidean artery. It 

 is however almost certain that it is simply a special development of 

 some commissural vessel related to this arch, and a sufficient cause for 

 its special development would seem to be the strangling and conse- 

 quent obstruction of the main hyoidean artery at the point where it 

 passes through the foramen in the hind edge of the skull. The blood 



33* 



