118 EDWARD php:lps ALLIS jr , 



The common carotid artery, in 12 mm larvae, arises, as it does 

 in older larvae and in ttie adult, from the efferent artery of the first 

 branchial arch, as that artery curves mesially and backward to join, 

 first the efferent artery of the secoud branchial arch and then, united 

 with that artery, the anterior end of the median, dorsal aorta. The 

 lateral halves of the dorsal aorta have thus, at this age, not yet 

 united as far forward as the second branchial aortic arch. In 35 mm 

 specimens the union extends forward beyond that arch, as shown in 

 fig. 28 of my earlier work. 



Running forward the common carotid, in 12 mm larvae, soon 

 separates into its two portions , the external and internal carotids. 

 The external carotid is, at this age, much the smaller of the two, 

 and traverses at once its small foramen, which leads into the upper, 

 lateral chamber of the eye-muscle canal. Here the artery runs for- 

 ward, upward, and laterally close against the inner surface of the 

 cartilage of this part of the skull, between it and the ventro-lateral 

 surface of the large trigemino-facial ganglion, gives off' one or more 

 branches, and reaches the ventral edge of the trigeminal foramen. 

 There it turns laterally, through the trigeminal foramen, and passes 

 #dorsal to, and close to, the extreme anterior end of the pseudo- 

 branchial chamber. It then runs downward and laterally, close to 

 the ventro-posterior aspect of the truncus trigeminus, and reaches 

 the mesial surface of the anterior edge of the superficial division ot 

 the adductor mandibulae. There it continues onward but was not 

 further traced. It is thus, in its distribution, a mandibular or maxil- 

 lary vessel, 



The internal carotid, after its separation from the external carotid, 

 runs forward and slightly mesially along the ventral surface of the carti- 

 laginous cranium, lying immediately lateral to the lateral edge of the para- 

 sphenoid. It is here accompanied by the pharyngeal branch of the uer- 

 vus glossopharyngeus, the nerve lying immediately mesial to the artery. 

 Continuing forward, both structures pass postero-ventral to the ramus 

 palatinus facialis as that nerve issues from its foramen, and beyond 

 the foramen lie immediately mesial to the nerve. In the adult the 

 artery and its two associated nerves here lie in the posterior portion of 

 the so-called palatine canal of my descriptions, between the parasphenoid 

 and the base of the chondrocranium. In the 12 mm larva cut in 

 transverse sections, the pharyngeal branch of the glossopharyngeus 

 alone, of the three structures, here lay internal to the parasphenoid, 

 on one side of the head, while on the other side the carotid artery 



