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of the commissural vessel, runs forward and slightly mesially along 

 the lateral edge of the ventral surface of the chondrocranium , and 

 soon gives off its external branch. According to Ayers' descriptions 

 this external carotid artery arises from the commissural vessel from 

 the eff'erent hyoidean artery (Ayers' common carotid) before that vessel 

 falls into the dorsal aorta; a totally ditferent arrangement from what 

 I find on both sides of each of my two specimens. 



The external carotid, after its origin from the common carotid, 

 almost immediately gives off an important branch which corresponds 

 to the orbital artery of Parker's (1886) descriptions of Mustelus. 

 This artery supplies the muscles and tissues of the orbit, one branch 

 passing dorsal to the ophthalmica magna and then ventral to the 

 nervus opticus and another dorsal to the latter nerve, a small branch 

 of the latter branch running forward ventral to the nervus opticus, 

 the eye-stalk, and the ophthalmica magna artery and then across the 

 floor of the orbit onto the ventral surface of the preorbital portion of 

 the chondrocranium. The external carotid, having given off this orbital 

 branch, soon separates into two branches; a mandibular one which 

 runs downward into the mandible, and a maxillary one which runs 

 forward across the outer margin of the orbit, ventral to the eye-ball, 

 and then onward between the upper jaw and the base of the chondro- 

 cranium. A delicate terminal branch of the maxillary artery meets 

 in the median line and anastomoses with its fellow of the opposite 

 side, a small median branch then being sent backward to dense tissue 

 of the region. 



The internal carotid, which is the anterior prolongation of the 

 lateral dorsal aorta beyond the point of origin of the external carotid, 

 runs forward and mesially along the base of the chondrocranium and, 

 not far from the median line, traverses a foramen in the base of 

 the skull and enters the cranial cavity. This foramen seems not to 

 be given in Goodey's (1910) descriptions of the skull of the fish, 

 although it may be the foramen called by him the interorbital sinus. 

 This I shall have to determine by further study. Having entered the 

 cranial cavity, the internal carotid meets in the median line and ana- 

 stomoses with, or is connected by short commissure with, its fellow 

 of the opposite side, and then immediately turns directly laterally, and 

 then forward and laterally in the cavity. There it is soon joined by 

 the efferent pseudobranchial artery, which artery enters the cranial 

 cavity by traversing a foramen in the orbital wall immediately antero- 

 ventral to the base of the eye-stalk; this foramen apparently being the 

 internal carotid foramen of Goodey's descriptions. Whether the in- 



