62 ALLEN 
a superficial one. Even though the cephalic portion of the 
internal carotid crosses the tract of the external carotid and a 
branch of one anastomoses with a branch of the other, still, in 
the main, the internal carotid supplies the region of the internal 
carotids of the Mammalia. It certainly extends no farther 
cephalad than the exteral carotids. For these reasons, in 
Ophiodon, it seems advisable {to retain {the names internal and 
external. 
4. Opercular and Dorsal Branchial Muscle Arteries. 
These vessels are 2 very constant arteries, which arise from 
the dorsal part of the second efferent branchial artery. 
Of the, thevopercular artery (P\.1, fis. 1;.Op.A.) asthe 
most dorsal and cephalic vessel. It arises from the anterior 
surface of the second efferent branchial artery near its point of 
union with the first efferent branchial artery; its course is first 
cephalad for a short distance, passing over the second obliquus 
dorsalis muscle, to which it gives a branch; then curving dor- 
sad, sends off a cephalic branch, which supplies the first inter- 
nal branchial levator muscle (Levatores arcuum branchialium in- 
terni of Vetter) and the first obliquus dorsalis muscle; and a little 
farther up, a third artery is given off to the 4 outer branchial 
levator muscles (Levatores arcuum branchialium externi of 
Vetter). Then continuing dorsad, laterad to the first efferent 
branchial artery and jugular vein, it sends off a caudal branch 
to the levator operculi muscle of Vetter, and when the level of 
the opercular is reached, terminates by running ventrad along 
the inner surface of this bone. 
The vessel, which is designated as the dorsal branchial mus- 
cle artery (Pl. 1, fig. 1; Br.M.A.), but which supplies fewer 
branchial muscles than the one designated as the opercular 
artery, arises from the posterior surface of the second efferent 
branchial artery directly below the opercular artery. Its course 
is caudad, passing behind the second internal branchial levator 
muscle, and over the third and fourth obliqui dorsales muscles, 
it sends off a branch to each. Then after crossing over the 
fourth efferent branchial artery it curves ventrad, supplying the 
occipito-clavicularis muscle, the pharynx, and the dorsal part of 
the pharyngo-clavicularis internus muscle. 
