MANDIBULAR ARTERY AORTIC ARCH 113 



appear as a single artery. It is however evident that the fusion 

 of these two vessels, their origin ventrally from the lateral 

 hypobranchial artery, and their connection, between these two 

 points, in Chlamydoselachus, by a cross-commissural vessel, 

 all suggest that the so-called afferent mandibular artery may not 

 be a persisting portion of the primitive mandibular aortic vessel, 

 as all embryological investigations would seem to establish, but 

 a posterior efferent, or secondary afferent mandibular artery 

 similar to the secondary afferent arteries that I have described 

 in the hyal arch of Amia and certain teleosts (Allis, '12 a). This 

 would then account for the position of the artery, in Chlamydo- 

 selachus, posterior to the 'joint ligament' of Goodey's descrip- 

 tions; for, if the ligaments connecting the mandibular and hyal 

 arches are developed, as I have recently suggested ('15 ), from 

 tissues that represent the undeveloped branchial rays of the 

 mandibular arch, the primitive afferent mandibular artery would 

 normally lie anterior, instead of posterior, to the ligament. This 

 must be determined by further embryological study of thes# 

 vessels, and it is well to bear in mind, in this connection, Kelli- 

 cott's description of the development of the definitive anterior 

 hyal artery in Ceratodus. He says ('05, p. 202) : 



So that while no direct observations could be made bearing upon 

 this point, all the circumstances point to the development of a branch 

 from the anterior efferent artery of the first branchial arch up- 

 ward, forming the (definitive afferent) hyoidean artery. The efferent 

 (epibranchial) hyoidean artery is derived from the hyoidean aortic 

 diverticulum and is the anterior carotid artery. The vessels of the 

 hyoid arch of the adult Ceratodus therefore represent a second set of 

 vessels and are not comparable with the vessels of other forms— 

 particularly the other Dipnoi, where, as already pointed out, the hyoid 

 vessel appears as one of the original afferent branchial series. ' 



The artery that, in Chlamydoselachus, runs forward across 

 the external surface of the musculus adductor mandibulae to 

 fall into the mandibular branch of the carotis externa is appar- 

 ently, as already stated, a direct anterior prolongation of the 

 cross-commissural vessel from the hyal to the mandibular arches. 

 If that portion of the carotis externa which lies immediately 

 dorsal to the point where it is joined by this cross-commissure 



JOURNAL OF MORFHOI.OGV. VOL. 27, NO. 1 



