516 



current in the main artery being obstructed, a secondary connection 

 with the lateral dorsal aorta has been established. 



The afferent mandibular artery has, as already described, become 

 secondarily connected with the ventral end of the efferent hyoidean 

 artery. Running forward it soon gives off three branches, close to- 

 gether, and then turns upward along the anterior edge of the cerato- 

 hyal. One of the three branches given off at the bend runs upward 

 in the hyoidean arch, supplies muscles of the region and apparently 

 represents the anterior efferent vessel of that arch. The other two 

 branches run forward and doubtless supply the thyroid and thyroid 

 region. The afferent mandibular artery itself continues upward along 

 the anterior edge of the ceratohyal and beyond the dorsal end of that 

 element continues onward toward the pseudobranch, but it quite cer- 

 tainly does not reach that organ or communicate, at any point, with 

 the afferent pseudobranchial artery, to be later described. At about 

 the level of the dorsal end of the ceratohyal the afferent mandibular 

 artery gives off a large branch, this branch being much larger and 

 more important than the direct continuation of the artery itself. 

 Running forward and upward this large branch reaches the region of 

 the angle of the mouth and there separates into two parts, one of 

 which goes to the maxillary region and the other to the mandible. 



The median dorsal aorta runs forward, as Ayers has shown it, 

 a considerable distance beyond the point where it is joined by the 

 efferent arteries of the first pair of branchial arches. In this part of 

 its course it is of considerably smaller caliber than it is posteriorly, 

 and when it reaches the hind edge of the chondrocranium it separates 

 into two parts, a lateral dorsal aorta on either side. These two lateral 

 aortae are called by Ayers the third pair of aortic roots, and arising 

 between them, as a direct anterior prolongation of the median dorsal 

 aorta, that author shows and describes a small median vessel which 

 he calls the cranial aorta. No trace whatever of such a vessel could 

 be found in either of my two specimens, notwithstanding that it was 

 most carefully and particularly looked for. Running forward and 

 slightly laterally, immediately beneath the broad and rounded base of 

 the chondrocranium, the lateral aorta of each side is joined by the 

 corresponding efferent hyoidean artery, and then soon turns sharply 

 laterally and, at the edge of the base of the chondrocranium, receives 

 the commissural vessel, just above described, from the efferent hyoidean 

 artery; this commissural vessel being considerably larger than the 

 lateral aorta. The latter vessel, now becoming the common carotid, 

 turns sharply forward, at an acute angle, in the direction prolonged 



