Ppeudobranchial aud Carotid Arteries in the Gnathostome Fishes. 117 



under the assumption that a portion of this carotid artery is developed 

 from remnants of the ventral portion of the premandibular aortic arch, 

 the branch that goes to the pseudobranch is shown in the accompanying 

 diagram in the position of an intermediate commissure between that 

 arch and the mandibular arch. 



The external carotid, if it represents, as T have suggested, a 

 dorsal nutritive or muscle branch, would seem to here, in Amia, 

 represent such a branch of the efferent glossopharyngeal rather 

 than of the efferent hyoidean artery. In Anieiurus and Ccmtodus,. 

 the artery has an independent origin from the former artery, as 

 will be later described. 



l^he next posterior vessel that arises from the dorsal aortic 

 trunk, here still called the common carotid, is the artery described 

 by me as the hyo-opercularis, and this artery has been shown by 

 me (Allis, 1900) to be a dorsal remnant of the hyoidean aortic 

 arch. It sends certain branches downward in the hyoidean arch^ 

 and a small branch forward through the trigemino-facialis chamber 

 and then forward and downward with the external carotid (Allis^ 

 1897). 



The next posterior vessel is the efferent artery of the first 

 branchial arch, which acquires in Amia, as in selachians, a ventral 

 connection with the ventral end of the afferent mandibular artery. 

 The latter artery then supplies, for a time, arterial blood to the 

 pseudobranch, but after that organ acquires a connection with the 

 external carotid the afferent mandibular artery diminishes in im- 

 portance, and apparently, in the adult, has wholly lost its connection 

 with the pseudobranch. The ventral portion of the mandibular 

 artery, however, persists as an artery supplying certain regions, as 

 does also the ventral portion of the hyoidean artery; this latter 

 artery being distributed to the operculum. 



In teleosts, the arteries, as described by various authors^ 

 vary considerably in detail but not, apparently, in principle. In 

 Fig. 11 the arrangement of the vessels in the Loricati, as de- 

 scribed by Allen (1905) and myself (in press), is given, and it 

 is so closely similar to that in Amia that no general description 

 is necessary. The only important differences are ; that the ventral 

 portion of the mandibular aortic arch is retained as an afferent 

 pseudobranchial artery; that the afferent pseudobranchial branch of 

 the external carotid joins the afferent mandibular artery below the 

 pseudobranch instead of at that organ; that the dorsal portion of 



