2i8 ALUS. [Vol. XVIII. 



sented by a line of degenerate muscle tissue, the fibers of which 

 are arranged transversely to the arch, that is, lying in the same 

 direction as the gill rays. This tissue extends a short distance, 

 both distally and proximally, from the posterior angle of the arch, 

 gradually diminishing in size and finally disappearing entirely. 



The specialized muscles (Fig. 44) are found as a series of well- 

 developed muscles lying along the inner face of each branchial 

 ray, and hence radial to the arch. Each muscle arises, by a long 

 tendon, from the outer surfaces of the bases of two adjoining 

 rays of one row of filaments, runs outward between those rays, 

 and, beyond their flattened basal portions, becomes a well-devel- 

 oped but slender muscle which passes between the rays from 

 which it arises and is inserted on the inner face of a ray belong- 

 ing to the opposite row of filaments. The rays of the two rows 

 of filaments alternate, as already described, so that the ray on 

 which the muscle is inserted lies opposite the interspace between 

 the two rays from which it arises. The insertion of the muscle 

 extends some distance along the shaft of the ray. The action 

 of these muscles is simply to pull the two rows of filaments to- 

 gether. 



The definite innervation of any of the interbranchiales could not 

 be determined. 



4. Muscles Innervated by the Occipital and First Spinal Nerves. 



The Sternohyoideus (Sh, Fig. 49) of each side of the head 

 arises from the inferior end of the corresponding clavicle. Run- 

 ning almost directly forward it is inserted on the posterior por- 

 tion of the lateral surface of the sternum, the surface of insertion 

 extending, in its ventral portion, about one half the length of the 

 bone, but in its dorsal portion only about one third or one quarter 

 of its length. The ventral edges of the muscles of the two sides 

 of the head touch each other in the middle line through nearly 

 their entire length. Their dorsal edges touch each other through 

 about one third of their length. There is, however, no interchange 

 of fibers between the two muscles. The ligament that connects 

 the anterior ends of the clavicles of the two sides of the head with 

 the hind end of the sternum lies between the two muscles. 



The muscle of each side arises mainly from the antero-Iateral 



