Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 107 



The Intercalar (IC) is a thin, scale-like bone of irregular and 

 variable shape. Its hind edge, which is its thickest portion, is 

 usually straight or slightly concave, and has, at about the middle 

 of its length, a more or less pronounced eminence, which gives 

 articulation to the lower end of the leg of the suprascapular. 

 From the base of this process a more or less pronounced ridge 

 runs forward across the outer surface of the bone, and marks the 

 upper limit of the surface of insertion of certain of the levator 

 muscles of the branchial arches. The bone lies upon the lateral 

 surface of the adjoining portions of the squamosal, petrosal and 

 occipitale laterale, fits into slightly depressed regions on those 

 bones, and a part of its outer edge fits under thin, laminar, splint- 

 like processes of the petrosal and occipitale laterale, as already 

 stated in describing those bones. The intercalar extends poste- 

 riorly, in its middle portion, beyond the adjoining hind edges of 

 the squamosal and occipitale laterale, and so has a small, somewhat 

 crescent-shaped surface presented dorso-mesially. It takes no 

 part whatever in the formation of any of the semicircular canals. 



The intercalar of Scomber is thus, to all appearance, simply a 

 membrane bone, as it is in Amia (No. 4, p. 688). It accordingly 

 offers no support whatever to Sagemehl's statements regarding 

 the primary character of the bone in other teleosts (No. 65, p. 45), 

 but supports, on the contrary, in every particular, Vrolik's earlier 

 statements and conclusions regarding it (No. 76, p. 285). That 

 the bone, in Scomber, can have, or can have had, any primary rela- 

 tion whatever to any part of the ear capsule seems even more im- 

 probable than in Ainia. 



The Extrascapular (ESC, Fig. 5) is a delicate, slender, Y- 

 shaped bone lying in the deeper layers of the skin on the dorsal 

 surface of the posterior portion of that anterior extension of the 

 trunk muscles that fills the temporal groove. The shank of the 

 Y-shaped bone is directed backward, and overlaps the antero- 

 lateral edge of the suprascapular at about the middle of the total 

 length of that bone. The shank and lateral arm of the Y form a 

 nearly straight line, which runs almost directly forward and ends 

 immediately behind the enlarged hind end of the dorsal ridge of 

 the squamosal. The mesial arm of the Y runs forward and 

 mesially, superficial to one or two anterior, splint-like processes 



