•214 ANATOMY OF VERTEBRATES. 



ih. r, arising from the outer part of the scapula and from the 

 parapophyses of succeeding vertebrae, is inserted by similarly 

 disposed, but more slender tendons. At their termination, each 

 tendon bifurcates, allowing that appropriated to the succeeding 

 vertebra to pass through it, so that, all, save the last, are both 

 perforati and perforantes. The protractor scapula, ib. i, be- 

 comes, when antagonised by the two foregoing muscles, the 

 chief elevator of the head. Of the two muscles of the ros- 

 trum in the Ray, the superior, levator rostri, arises from the 

 scapula by a short fleshy belly ending in a slender round tendon 

 which runs above the branchiae in a synovial sheath to the rostral 

 cartilage, which it serves to raise : the inferior, depressor rostri, 

 arises from the lower part of the coalesced anterior vertebras, runs 

 obliquely outward, and then curves inward to its insertion into the 

 lower part of the base of the rostrum. The muscles of the jaws 

 in the Rays include, with maxillp-mandibulares', those answering 

 to I and m in the Shark, fig. 132. The depressor mandibuli is a 

 large oblong mass of parallel longitudinal fibres, arising from the 

 lower (coracoid) part of the scapular cincture, and passing forward 

 to be inserted into the mid part of the mandible. Two small mus- 

 cles, one on each side, contribute to depress the mandible : they 

 are attached in front near the commissure of the lips, and, running 

 inward, almost cross each other beneath the great depressor. A 

 third muscle has its fibres remarkably interlaced, but divisible into 

 three chief fascicles, two of which are anterior and one posterior : 

 this is derived from the end of the upper jaw and joins the hinder 

 margin of the second mass. The first portion is situated in front 

 and above the maxilla, near its commissure, and runs obliquely to 

 join the outer edge of the second fascicle : all co-operate in firmly 

 closing the mouth. The protractor oris forms a pair of long and 

 slender muscles passing from the rostrum between the cranial base 

 and the palate to be inserted into the maxilla. The muscles of 

 the vast pectoral fins form two thick fleshy layers, covering its car- 

 tilages above, fig. 139, t, and below, and dividing into as many 

 fasciculi as there are fin-rays, into which they are inserted. A 

 similar arrangement obtains in the muscles of the ventral fins, ib. v. 



The muscles, in Fishes, of the eye-ball, the air-bladder, and of 

 some other special organs, will be described with the parts they 

 move. 



The muscular tissue (myonine) of fishes is usually colourless, 

 often opaline, or yellowish ; white when boiled : the muscles of 

 the pectoral fins of the Sturgeon and Shark are, however, deeper 

 coloured than the others ; and most of the muscles of the Tunny 



