G8 SUPPLEMENT ON 



muscles of the pectoral fin are in two layers on each superficies, 

 slightly crossing over each other, and terminating in tendinous 

 slips among the rays ; the superficial anterior coming from the 

 humeral descends, the internal from the cubital bone ascends; 

 and the reverse obtains at the back part of the fin. The 

 bones of the pelvis are attached to the slender inferior mus- 

 cles before noticed, and by transverse muscles in some spe- 

 cies, where these bones are not united ; but the ventral fins 

 possess levators attached to the superior surface of the bones 

 of the pelvis, and depressors to the inferior surface ; forming 

 two layers on each side, resembling those of the pectorals, 

 and their serrated insertions between the rays having one 

 externally to spread the fin. 



The jaws are acted upon by one single mass of muscle, 

 which closes them by drawing them together. It adheres to 

 the whole external surface of the posterior part of the palato- 

 teinporal arch, with till its bones, including the anterior edge of 

 the preoperculum ; from its anterior edge two tendons united 

 by aponeuroris proceed ; that from the superior angle to the 

 superior maxillary bone, the inferior to the lower jaw, behind 

 the coronoid process. In cartilaginous genera, there is, how- 

 ever, considerable difference. The lower jaw, having no 

 digastric muscle, is opened only by means of the simultaneous 

 action of the muscles which pass from the shoulder to the 

 hyoid, and thence to the jaw. This last muscle resembles the 

 genio-hyoidean ; but as in many species the lower jaw has the 

 power of approximating its two branches, there is a muscle 

 proper for that office, placed transversely in the angle which 

 they form. 



The muscles of the palato-tympanic arch are, 1st, one occu- 

 pying the roof of the palate, consisting of transverse fibres pass- 

 iiiu from beneath a part of the sphenoid and great ala to the 

 superior border and internal face of the arch, &c. It lowers, 

 and brings the arches closer together, compressing the space 



