Nos. IAXD2.] AXATOMV OF SCOMBER SCOMBER. 205 



slightly beyond it onto the lateral surface of the petrosal above 

 and posterior to the facial foramen. The origin of the third ex- 

 ternus occupies a narrow band across the anterior end of this sur- 

 face, lying sometimes almost entirely on the petrosal. The origin 

 of the fourth externus occupies a similar, but narrower and longer 

 band across the hind end of the surface. The two interni occupy 

 the whole surface between these two terminal bands, the surface 

 of origin of the anterior internus lying immediately ventral to the 

 posterior two thirds of that of the posterior muscle. 



The externi of the first and second arches (Labc. I-II.) arise, 

 with the ligament (lad. I.) that connects the first arch with the 

 side .wall of the skull, from the lateral surface of the skull immedi- 

 ately below and behind the facial foramen. The surface of origin 

 of these muscles is oval in form, and lies mostly on the petrosal, but 

 it extends backward slightly beyond that bone onto the anterior 

 end of the intercalar. The surface of origin of the first externus 

 occupies the ventral and larger part of this surface; that of the 

 ligament lies immediately dorsal to that of the first externus ; and 

 that of the second externus immediately antero-dorsal to the other 

 two. 



The fifth externus {Lobe. V.) arises from the posterior portion 

 of the lateral surface of the intercalar, immediately above the 

 suprascapular process of that bone. It shares this origin with 

 a part of the fibers of the first muscle segment of the trunk, the 

 surface of origin of the latter muscle extending dorsally onto the 

 posterior process of the squamosal. 



The anterior internus runs mesially and downward internal to 

 the dorsal end of the posterior internus, and postero-internal to 

 the suprapharyngobranchial of the first arch, and is inserted 

 along the dorsal edge of the second infrapharyngobranchial. 

 The surface of insertion of the muscle occupies the postero- 

 dorsal edge of the small depression that lies between the two 

 cartilaginous portions of the dorsal edge of the element, the 

 antero-ventral part of the depression giving insertion to the 

 obliquus dorsalis of the first arch. On the dorsal edge of 

 the postero-mesial surface of the infrapharyngobranchial, ad- 

 joining the surface of insertion of the anterior internus, the 

 obliquus dorsalis of the second arch has its insertion. The in- 



