— 206 — 



The so-called quadrates of osseous fishes are thus not all equivalent structures. The articula- 

 tions of the mandible with the suspensorial apparatus are also not all similar; Amia being the one 

 known exception to the otherwise general rule, but Lepidosteus somewhat resembling it. A further 

 development of the conditions found in Amia might transfer the mandibular articulation from the 

 palato-quadrate to the hyomandibular. 



10. On the hind edge of the metapterygoid, in all of the mail-cheeked fishes examined ex- 

 cepting Cottus and Dactylopterus, there are two flanges, apparently of membrane (exosteal) origin, 

 one of which is lateral and the other mesial in position. Between these two flanges the external 

 carotid artery runs downward to fall into the arteria hyoidea shortly before that artery joins the 

 opercular hemibranch, and after it has passed from the external to the internal surface of the 

 palato-quadrate apparatus. On the opposing surfaces of the two flanges the lavator arcus palatini 

 muscle has the larger part of its surface of insertion. 



In Cottus and Dactylopterus these two flanges, instead of being one lateral and the other 

 mesial, are respectively one ventral and the other dorsal; both flanges lying in the plane of the 

 body of the metapterygoid, with their adjoining edges fused but perforated by a foramen which 

 transmits the external carotid and represents the V- shaped space between the flanges in the other 

 fishes. In these two fishes the flanges appear to be of endosteal rather than of exosteal origin. 



In Amia the lateral one of these two flanges is represented in the so-called metapterygoid 

 process of the metapterygoid, the mesial flange being represented in that part of the body of the 

 metapterygoid that lies posterior to the process. In Amia both these parts of the bone are quite 

 evidently of endosteal origin. 



11. In all of the mail-cheeked fishes examined there is a vessel, apparently an artery, that 

 arises in connection with what seem to be either glomuses or rudimentary glandulär structures 

 related to the efferent arteries of the first three branchial arches. Certain evident connections of 

 these glomuses with the lymphatic vessels were found, and occasional apparent connections with 

 the arteries, but no indication whatever of a connection with the venous System. The vessel 

 parallels the common carotid and its branches, and peripherally the walls of the branches of the 

 vessel change abruptly in character, and there appear as lymphatic Spaces. The fact that the 

 external carotid branch of the vessel traverses the trigemino- facialis Chamber in much the position 

 of the hyo-opercularis artery of Amia, led me at first to homologize the vessel with that artery, 

 but as there is much doubt of the correctness of this homologization 1 have described the vessel as 

 the vessel x. In Dactylopterus one branch of the vessel seemed to enter the opercular hemibranch. In 

 Polyodon the system is much more developed than in the mail-cheeked fishes, and I am investigating 

 it in that fish. It would seem as if the glomuses from which the vessel arises might be serial 

 homologues of certain of the nephritic structures, and possibly also homologues of the so-called 

 thymus of Polypterus. 



12. The external carotid, in all the fishes examined, traverses the trigemino-facialis Chamber, 

 gives off several branches, and then terminates in a branch which turns downward between two 

 flanges on the hind edge of the metapterygoid and falls into the arteria hyoidea shortly before that 

 artery enters the opercular hemibranch. This terminal portion of the external carotid corresponds 

 closely in position to, and is probably the homologue of the secondary afferent pseudobranchial artery 

 of my descriptions of Amia, and its connection with the arteria hyoidea, instead of with the 

 pseudobranch, woiüd give origin to the teleostean arrangement. 



