489 



T-shapecl structure, each arm of the T having on its anterior surface, 

 near its dorsal end, a tit-like projection. From each of these tit-like 

 projections a small artery has its origin, this artery being, morpho- 

 logically, the anterior prolongation of the internal carotid of its side. 

 Each internal carotid runs upward forward and laterally in a separate, 

 lateral branch of the large median canal in the cartilage, and there 

 soon receives the efferent pseudobranchial (mandibular) artery, which 

 artery, to reach the carotid, traverses a short and independent per- 

 foration of the side wall of the chondrocranium. 



The dorsal edge of the large median vessel formed by the fusion 

 of the internal carotids of opposite sides is firmly attached, by connec- 

 tive tissue, to the ventral surface of a large transverse vessel which 

 traverses the canahs transversus of Gegenbaur's descriptions, the 

 carotid canal and canalis transversus being, in my two specimens, 

 in free communication with each other. From the middle point 

 of the canalis transversus a small median canal leads upward into 

 the cranial cavity and is traversed by a small median branch of the 

 vessel that traverses the canal. 



The internal carotid, after receiving the efferent pseudobranchial 

 artery, continues onward, traverses the remaining portion of the 

 cartilage of the base of the chondrocranium and enters the cranial 

 cavity by a foramen that lies in the floor of the pituitary fossa, 

 close to but not confluent with its fellow of the opposite side. 



Having entered the cranial cavity the internal carotid becomes 

 the arteria cerebralis, which, running forward, immediately gives off 

 its optic branch (arteria centralis retinae), that branch leaving the 

 cranial cavity with the nervus opticus. The remainder of the artery 

 then separates into anterior and posterior branches, the posterior 

 branches of opposite sides uniting posteriorly to form a single median 

 myelonal artery. 



The efferent pseudobranchial (mandibular) artery has its origin 

 from the pseudobranch and, as above described, traverses a separate 

 and independent canal in the side wall of the chondrocranium to reach 

 and empty into the internal carotid. Immediately before entering 

 this canal in the chondrocranium it gives off the arteria ophthalmica 

 magna, which goes direct to the eye-ball. 



Parker, in his descriptions of Mustelus antarcticus (1886), 

 calls the efferent pseudobranchial (mandibular) artery the anterior 

 carotid, and this artery, together with the definitive afferent pseudo- 



