124 Edward Phelps Allis jr., 



and Weight seems to fulh- confirm this latter statement by his own 

 statement that the internal carotids do not form a circulas cephalicus. 

 But as Weight also saj's that there is no circulus cephalicus in 

 Amia, in which fish an intracranial connection between the two 

 carotids is found, this latter connection may possibly also be found 

 in Lepidosteus. 



Of Acipenser the only descriptions I have are b,y Johannes 

 MuLLEE (1839) and Viechow (1890), aud these two descriptions do 

 not wholly agree. According to Müllee the afferent hyoidean artery 

 is a branch of the afferent artery of the first branchial arch, while 

 according to Viechow, it would seem to be a prolongation of the 

 posterior efferent artery of that arch, the branch being called by 

 Viechow the ramus opercularis. Assuming Viechow^ to be correct, 

 I have tried to give, in the accompanying Fig. 13, the vessels as he 

 describes them ; but as Viechow gives no figures, does not describe 

 all the branches mentioned, and does not even give the order in 

 which the branches arise from the several arteries, the diagram is 

 simply tentative. 



The arteria retrohyomandibularis of Viechow's descriptions is 

 said to arise "aus dem Stamme, welcher von der ersten Aorten- 

 wurzel (A. efferens branchialis 1) nach vorn läuft", and as the trunk 

 (Stamme) here referred to must be the posterior carotid of Müllee's 

 descriptions, the arteria retrohyomandibularis is probably the homo- 

 logue of the external carotid of Amia and Lepidosteus. This retro- 

 liyomandibularis artery of Acipenser is said to give off', first of all, 

 a strong branch to the M. protractor hyomandibularis, after which 

 one branch is sent to the M. retractor hyomandibularis and oper- 

 cularis, and another backward to the hyoidean gill. A second branch 

 to the hyoidean gill may be sent backward from the branch to the 

 M. retractor hyomandibularis and opercularis, but as this is said not 

 to be constant, the branch is represented by dotted lines in ray 

 diagram. What the further course and distribution of tlie artery 

 is Viechow does not say, but as the artery, in drawings that I 

 have of Pohjodon, is shown running forward dorsal to the nervus 

 opticus, I so show it, in dotted lines, in Acipenser. 



Viechow considers the arteria retrohyomandibularis as one of 

 two arteries that must represent the efferent artery of the hj^oidean 

 arch; the other artery being a vessel that extends from the hyoidean 

 gill to the efferent glossopharyngeal artery, but said by Viechow 

 to be of inconstant occurrence. This second supposition I consider 



