434 C. H. DANFORTH 



ARTERIES OF THE PHARYNX 



Each efferent branchial artery on approaching the roof of 

 the pharynx leaves its groove in the epibranchial cartilage and 

 crosses the anterior aspect of the m. levator arcus branchialis 

 (m. lev. 1, fig. 7). Medially it turns ventrally and somewhat 

 posteriorly around the muscle a little proximad of its insertion. 

 The relations with the cartilages vary somewhat in the different 

 arches (fig. 15). The first passes through a triangular space 

 bounded dorso-medially by the parasphenoid bone, antero-lat- 

 erally by the first pharyngobranchial, and postero-laterally by 

 the anterior end of the first epibranchial and second pharyngo- 

 branchial cartilages. Within this triangular space it gives rise 

 to the common carotid artery (a.cc). Leaving the triangle it 

 crosses the medial part of the second pharyngobranchial, making 

 a groove in its ventral surface to gain the deep median exca- 

 vation between the wings of the parasphenoid behind. It unites 

 with the corresponding vessel of the other side in a plane passing 

 near the middle of the third pharyngobranchials. The third 

 pharyngobranchial does not reach the parasphenoid above and 

 so a triangle corresponding to the one in front is not completely 

 closed in behind. This allows the second efferent artery to 

 slip back to a more posterior position as shown in the figure. 

 It reaches the median vessel in the plane of the end of the third 

 epibranchial cartilage. The third and fourth vessels likewise 

 have migrated somewhat backwards. All of these arteries are 

 forced to make a ventral dip around the knife-like edge of the 

 parasphenoid. On reaching the mesial side of the wing of that 

 bone they turn abruptly upward and backward to enter the 

 median vessel on its ventral side. The arrangement of these 

 vessels, each separately emptying directly into a single median 

 dorsal aorta, is in accord with some- of the other ganoids and 

 simpler sharks and is seemingly more primitive than the radices 

 aortae of higher sharks and teleosts. 



Pharyngeal branches of the main trunks are not well devel- 

 oped. There are, however numerous small twigs (fig. 15) that 

 supply the roof of the mouth and one prominent artery (a.vh.) 



