Pseudobraiichial and Carotid Arteries in the Gnathostome Fishes. 125 



as the partly correct one, the vessel referred to being- formed in 

 part by the efferent hyoideau artery, and in part by a dorsal com- 

 missure between that artery and the efferent glossopharyngeal arterj^, 

 as shown in my diagram in dotted lines. 



The afferent artery of the hyoidean arch, the ramus opercularis 

 of ViECHOw's descriptions, is said to be a branch of the lateral one 

 of two branches into which the ventral prolongation of the efferent 

 glossopharyngeal artery separates when it reaches the transverse 

 plane of the first gill cleft. What becomes of the median one of 

 these two branches is not stated. What remains of the lateral 

 branch, after the ramus opercularis is given off, is the afferent 

 mandibular artery, the afferent hyoidean and mandibular arteries 

 thus both here having acquired a secondary connection with the 

 ventral end of the efferent glossopharyngeal artery. Having separated 

 from the afferent hyoidean artery, the afferent mandibular artery 

 sends a branch to the M. constrictor and another to the corner of 

 the mouth (R. angularis), and then receives a commissural branch 

 from the hyoidean gill and becomes the afferent spiracular artery 

 of ViRCHOw's descriptions. 



ViECHOw does not describe an efferent spiracular (mandibular) 

 artery, but Müllee says that this artery separates into two parts, 

 one of which is the arteria ophthalmica (ophthalmica magna) and 

 the other an artery that supplies the brain ; branches of this latter 

 artery being said to join the posterior carotid. In mj diagram 

 these latter branches are shown as a single vessel which forms that 

 part of the internal carotid that lies between its point of separation 

 from the external carotid and the point where it is joined by the 

 dorsal end of the mandibular aortic arch. The distal portion of 

 what Müllee describes as the cerebral branch of the efferent 

 spiracular (mandibular) artery then becomes the anterior portion of 

 the internal carotid, as in Amia and selachians, and the ophthalmica 

 magna arises from the efferent mandibular artery as a branch of 

 that artery. The main blood-current to the brain accordingly goes 

 through the efferent pseudobranchial artery, as Müllee states, and 

 not through the internal carotid, but this, while it may constitute 

 a physiological peculiaritj^, does not constitute an anatomical one. 

 Ameiurus, as McKenzie has stated, resembles Acipenser in this 

 apparent origin of the encephalic arteries from the pseudobranch. 



In. Pohjodon the arrangement of the vessels apparently resembles 

 that in Amia, rather than that in Acipenser. this statement being 



