483 



region turns upward along the internal surface of the mandible. 

 There it lies between the mandibular and ceratohyal cartilages and 

 extends to the upper end of the latter cartilage, sending branches to 

 the tissues of the region, but, as in Mustelus and Chlamydoselachus, it 

 does not connect dorsally either with the pseudobranch or with the 

 definitive afferent pseudobranchial artery. The basal portion of this 

 afferent mandibular artery quite certainly represents a hyoideo-mandi- 

 bular section of the internal lateral hypobranchial, and the correspond- 

 ing artery in other selachians quite undoubtedly always lies internal 

 to the afferent hyoidean artery, as it does in both Heptanchus and 

 Chlamydoselachus, and not external to that artery as shown in one of 

 Parker's figures of Mustelus antarcticus and in Boulenger's re- 

 construction of those figures. 



The epibranchial portion of each efferent branchial artery appears 

 as a direct prolongation of the anterior artery of the related arch, 

 and each of these arteries, in the first four branchial arches, empties 

 independently into the dorsal aorta, on its ventral surface, close to 

 the corresponding artery of the opposite side of the head. The epi- 

 branchial arteries in the fifth and sixth branchial arches first unite to 

 form a short and common trunk, and this trunk empties into the aorta 

 on its ventral surface close to the corresponding trunk of the opposite 

 side. From the arteries of the first and third arches a small branch 

 has its origin, and goes to tissues of the region, these branches doubt- 

 less being the homologues of the dorsal branchial muscle arteries 

 of ganoids and teleosts (Allis, 1912). In the hyoidean arch, there 

 being no anterior efferent artery, the epibranchial portion of the 

 primary efferent artery, which is the posterior carotid of current 

 descriptions of selachians, appears as a direct prolongation of the 

 posterior efferent artery, and, running dorso-antero-mesially, falls 

 into the much smaller lateral dorsal aorta, as it does in the adult 

 Mustelus and Chlamydoselachus. 



In Chlamydoselachus, I considered the basal portion of the 

 so-called posterior carotid, which, in dissections, has decidedly the 

 appearance of being the epibranchial portion of the efferent hyoidean 

 artery, as being, quite certainly, a specially developed commissu- 

 ral vessel of some sort, the true dorsal end of the efferent hyoidean 

 artery being represented by a delicate vessel that arose, in both my 

 specimens of that fish, from the dorsal commissure that connects 



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