THE HEART AND ARTERIES OF POLYODON 435 



from the second efferent vessel which runs up over the wing 

 of the parasphenoid to the cartilage of the occipital region, where 

 it is distributed around the origin of the levator muscles and may 

 possibly send twigs through into the cranial cavity or anasto- 

 mose with others coming out. Allis describes this vessel as 

 coming from the first efferent artery; presumably it may arise 

 from either the first or second. Allis also describes a commissure 

 between the third and fourth efferent arteries. No large vessels 

 were found going back to the oesophagus. 



THE COMMON CAROTID ARTERY 



The common carotid (fig. 15, a.cc.) arises from the first efferent 

 branchial artery just in front of the anterior epibranchial carti- 

 lage. It is a short vessel which runs diagonally forward and 

 inward along the mesial aspect of the first pharyngobranchial, 

 near the end of which it may be said to terminate by dividing 

 into internal and external carotids. In the adult this division 

 is a very unequal one, the internal carotid, which arises from 

 the posterior and ventral side of the vessel, being so small that 

 it was at first entirely overlooked or mistaken for one of the 

 pharyngeal twigs that are given off in this region. The minute 

 internal carotid will be described further on in connection with 

 the artery from the pseudobranch; the distal continuation of 

 the main trunk from the end of the common carotid is here 

 described as the external carotid, even though the hypoopercu- 

 lar and orbito-nasal arteries are also involved. 



THE EXTERNAL CAROTID ARTERY 



The external carotid {axe. figs. 15, 16), appearing as a pro- 

 longation of the common carotid, continues around the anterior 

 end of the first pharyngobranchial cartilage in which it makes 

 a shallow groove. Laterally it passes through a rather large 

 foramen into a longitudinal channel, the facial canal of the basis 

 cranii. Here it gives off a large branch (a.hyo.) which follows 

 the hyomandibular nerve out posteriorly through the facial 

 foramen. The canal is produced forward beyond the point 



