No. 3.] MUSCLES AND NERVES [IN AMIA CALVA. 549 
articular in its lower, anterior part. This is the only connec- 
tion A2’ has with Aa, for although its deeper portion, where it 
passes to its insertion on the inner surface of the coronary 
cartilage, lies closely upon the outer surface of Ao, there is no 
interchange of fibres between the two muscles, and the r. max- 
illaris inferior trigemini lies between them, as shown in Fig. 
31, where A2’ has been entirely removed. 
Az", the middle portion of the muscle, is larger than either 
of the other divisions. Some of its outer, upper fibres are often 
inserted on the inner surface of the dentary, at the coronoid proc- 
ess and in front of it. The remaining fibres pass in large part 
directly into the ramus of the mandible, and there form the 
outer portion of the outer division, Aw’, of the mandibular 
muscle. A part of them, however, including the deepest and 
lowermost fibres, are inserted along the lower, ventral edge, and 
on the outer surface, of a broad tendon or fascia, 42 Aw’, which 
is formed on the inner surface of Az, where it contracts to pass 
into the mandible (Figs. 41 and 42, Pl. XXX). 
Az'", the upper, anterior division of Az, consists mainly of 
those fibres of the adductor that arise from the postorbital 
process, the surface of origin on this process being the deeper, 
lower, portion of the cap-like piece that forms the upper, outer 
angle of the ossification (No. 3, p. 480). It also contains those 
fibres of Az that arise from the under surface of the squamosal, 
immediately behind this cap-like piece, and some or all of those 
that arise from the under surface of the upper postorbital. 
The muscle is inserted entirely along the upper, dorsal edge, 
or on the outer surface of the upper half of the tendon Az Aa’. 
Although continuous at its origin with the upper, outer fibres 
of A", and at its insertion on Az Ao! with the deeper fibres of 
that muscle, it is, nevertheless, wholly distinct and separate 
anteriorly where there is no interchange of fibres whatever, the 
fibres of Az!” going entirely to the tendon Az Aa’, and those 
of A2" entirely to the inner surface of the dentary. 
In larvae of from 20 mm. to 50 mm. in length, 42!” arises 
entirely from the cartilage of the postorbital process, the sur- 
face of origin lying below the postfrontal bone, in front of the 
plane of the dorsal opening of the spiracular canal, and imme- 
