THE HEART AND ARTERIES OF POLYODON 439 



ventral side of the protractor and then between that muscle 

 above and the m. adductor mandibulae {m.adm.) below. In 

 this position it gives off a large branch which immediately sepa- 

 rates into posterior and anterior divisions. The former is a 

 nutrient artery to the m. adductor mandibulae, but the latter, 

 although supplying some muscular twigs, is distributed mostly 

 to the abundant fatty tissues and follows the palatoquadrate 

 forward to the median line. This recalls the vessel in Polypterus 

 which arises from the internal carotid and has recently been 

 considered by Allis ('08 b) as a possible remnant of the efferent 

 mandibular artery of that form. Here it is not likely that it 

 has any such significance. Further back the facial artery passes 

 over the lateral aspect of the m. adductor mandibulae and in 

 between the palatoquadrate cartilage and maxillary bone. Its 

 rather numerous branches, some of them muscular, are indicated 

 in figure 16. Below the angle of the mouth it still adheres to 

 the lateral surface of the muscle as the latter gains its insertion 

 on Meckel's cartilage. The main vessel finally becomes super- 

 ficial ventrally by emerging from between the cartilage and 

 overlying bone. From this point it may be traced forward 

 along the cartilage nearly to the median line. 



The next prominent branch (a.op.) from the external carotid 

 enters the region back of the orbit, and is apparently the one 

 designated by Allis as the ophthalmic branch. It gives a branch 

 to the rectus muscles of the eye, just as does a similar vessel 

 from the external carotid (orbito-nasal) of Lopholatilus and other 

 teleosts (Silvester), and divides into two main branches. One 

 of these supplies the fatty tissue behind and above the eye while 

 the other goes to the similar tissue medial and anterior to the 

 eye. Some of the terhiinal branches of the latter supply the 

 m. obliquus superior and others reach the nasal region, being 

 distributed apparently to a part of the sensory epithelium. 



Two other branches (fig. 16) arise from the external carotid 

 before it enters the rostrum. One of these runs ventral to the 

 orbit, supplying the m. obliquus inferior and the superficial tis- 

 sues below and in front of the orbit. The other has a somewhat 

 similar but more anterior distribution except that its largest 



