MANDIBULAR ARTERY AORTIC ARCH 105 



run upward along the outer face of the hyal arch immediately in- 

 ternal to the Ventral border of the mandible' ; and Parker adds: 



From the analogy of Callorhynchus it would seem, therefore, that the 

 mandibular artery is to be looked upon as a part of the original man- 

 dibular aortic arch, the rest of the ventral portion of which, represented 

 by the pseudobranchial artery, has acquired a secondary connection, 

 comparable to the transverse commissures, with the first efferent 

 branchial [posterior efferent hyal] artery. 



In all these earlier descriptions and conclusions there is thus 

 nothing to make one not previously so disposed even suspect 

 that the so-called mandibular artery, or arteria mandibularis, 

 of the adult selachian is not the persisting ventral, subcom- 

 missural portion of the aortic vessel of the mandibular arch 

 together with that branch of that aortic vessel which is said by 

 Dohrn to be distributed, in embryos, to the lower jaw. I have 

 accordingly so considered it in all my earlier works, and, seeking 

 to avoid confusion, have called the basal portion of the artery 

 the afferent mandibular artery, limiting the term mandibular 

 artery, as in current descriptions of the Teleostei, to the branch 

 sent to the lower jaw. I however suggested, in one of my 

 earlier works (Allis, '12 a, p. 135), that the origin of the per- 

 sisting afferent mandibular artery of the Teleostei from an ante- 

 rior prolongation of the lateral hypobranchial artery would sug- 

 gest that it 'might be primarily an efferent and not an afferent, 

 or aortic, vessel.' 



The conditions in the adult Chlamydoselachus, as shown in 

 the accompanying figures, may now be described. 



In the present specimen of Chlamydoselachus, as in the one 

 described in my earlier work, the lateral hypobranchial artery 

 (ventral lateral longitudinal commissure of the efferent branchial 

 arteries) continues forward beyond the posterior efferent artery 

 of the hyal arch, and, crossing the ventral surface of the cera- 

 tohyal, immediately gives off two branches, one of which runs 

 downward along the anterior edge of the ceratohyal and the 

 other upward along the same edge. The former goes to the 

 thyreoid gland and is the arteria thyreoidea properly so-called. 

 The other {aehy, fig. 2) runs upward between the ceratohyal and 



