Pseudobranchial and Carotid Arteries in the Gnathostome Fishes. 121 



may present the arrangement shown in my diagram, or either one 

 of the two afferent psendobranchial vessels there shown may be 

 wanting- (Johannes Müllee, 1839, and Maueee, 1884). The dorsal 

 afferent vessel may even arise as a separate and independent branch, 

 eitlier from the internal carotid, as in Gadus (Johannes Müller, 

 1839), or from the efferent glossopharyngeal artery, as in certain 

 specimens of Lophola Uns (Silvestee, 1904). Whether, in either of 

 these cases, the vessel is the homologue of the corresponding vessel 

 in the Loricati, or not, can not be told from the descriptions. That 

 this branch of the external carotid, as found in the Loricati, might 

 split off from the main artery, down to its root, and so become an 

 independent branch of the common or internal carotid, is evidently 

 possible, but unless it is split off in very early . embrj'onic 

 stages, it would certainly still have to pass through the trigemino- 

 facialis chamber, where such a chamber exists. In Lopliolatilus the 

 chamber is apparently present, for Silvestee says that his hyo- 

 opercularis artery "passes through the facial foramen" about 1 cm 

 from its point of origin", and Silvestee's hyo-opercularis, although 

 said by him to be the homologue of the artery so-called by me in 

 my descriptions of Amia, is the external carotid of those descriptions ; 

 Silvestee's external carotid being the orbito-nasal artery. In Gadus, 

 on the contrary, the trigemino-facialis chamber is wanting, or more 

 correctly, it exists but its outer wall is wholly membranous, as I 

 have fully explained in a work now in press. Here, then, it would 

 seem possible for a branch of the external carotid to split off' from 

 that artery and so acquire an independent origin from the internal 

 carotid. But, if Müllee's (1839) figures of Gadus be consulted, it 

 will be seen that it is much more reasonable to assume that the 

 afferent psendobranchial vessel, /", has been split off from the orbito- 

 nasal, than that it has been so split off from the external carotid. 

 If then the orbito-nasal artery of teleosts is, as I have suggested, 

 developed from the dorsal portion of the mandibular aortic arch, 

 the afferent psendobranchial artery of Gadus might represent a 

 persisting, but slightly modified condition of the primary relations 

 to the pseudobranch; or a reestablishment of such relations. And 

 that this may possibly be the case is suggested by the conditions 

 found in Ameiurus. 



In Ameiurus, the external carotid, as described by McKenzie 

 (1884), has an independent origin from the efferent glossopharyngeal 

 artery, near its dorsal end, and it does not apparently traverse a 



