108 Edward Phelps Allis jr., 



for a certain portion of the artery would naturally account for the 

 relation that the artery acquires, in certain teleosts and ganoids, to 

 the pseudobranch ; and in certain higher vertebrates certain branches 

 of the artery are actually derived from the ventral portions of the 

 mandibular and hyoidean aortic arches, as will be later explained. 



The external carotid of selachians, called by Paekee the 

 posterior carotid and b}' Carazzi the arteria orbitalis, first perforates 

 the cartilaginous hind wall of the orbit (Paekee, Htetl), and then 

 has a forward course apparently ventral to the nervus opticus. In 

 the Batoidei, it does not apparently perforate the hind wall of the 

 orbit, and it seems, in Hyetl's (1858) figures, to lie dorsal instead 

 of ventral to the nervus opticus. This difference in position of the 

 artery may be explained by the conditions found in Aniia, where the 

 main artery lies posterior and ventral to the nervus opticus, while 

 an ophthalmic branch of it passes dorsal to that nerve. The greater 

 development of the former or the latter of these two portions of 

 the artery of Ainia, would probably give rise to the conditions found 

 in selachians or the Batoidei, respectively. This will be again 

 referred to when describing the arteries in teleosts. 



Fig. 3 shows the arrangement of the vessels in the adult 

 Musielus antarcticus, as given by Parivee (1886). Here the posterior 

 efferent arteries of the hyoidean and first three branchial arches 

 are each connected by dorsal commissure with the anterior efferent 

 artery of the next posterior arch, and the ventral ends of all of the 

 efferent arteries, excepting onlj^ the posterior efferent of the fourth 

 branchial arch, are similarly connected by ventral commissures. 



The mandibular aortic arch has been separated into independent 

 dorsal and ventral portions. The ventral portion, called by Paeker 

 the mandibular arter}^ has lost its connection with the ventral aorta 

 (conus arteriosus) and acquired a secondary connection with the 

 ventral end of the efferent hyoidean artery. The dorsal portion 

 begins at the commissure that connects the hyoidean and mandibular 

 aortic arches, and extends upward through the pseudobranch to the 

 dorsal aorta; thus including a part of the afferent portion, and all 

 of the efferent portion of the aortic arch. The afferent portion of 

 the arch, and the hyoideo-mandibular commisure, together constitute the 

 pseudobranchial artery of Paekee's descriptions. The efferent portion 

 of the artery is represented in that part of Parker's anterior carotid 

 that extends from the pseudobranch up to the point where the 

 artery is said to give off a branch iv] Parker's anterior carotid 



