MYOLOGY OF FISHES. 



213 



The muscles of the jaws are very powerful, as might be expected 

 ill these fierce and predatory fishes. One, analoti'oiis to the ' tem- 



poral,' fig. 13i 



III, arises 



from the lateral and posterior ridge of 



139 



the cranium, and its fibres converge as they pass obliquely down- 

 ward and forward to their insertion into the mandible. They are 

 covered in great part l^y the stronger muscle ib. /, analogous to 

 the ' masseter,' which arises from the under part of the postfrontal 

 ridge, passes over the maxillo-mandibular joint, as over a pulley, 

 a.nd expands to its insertion in the lo"\ver side and ridge of the 

 hinder two-thirds of the mandible. Smaller muscles, ' inaxillo- 

 }iian(llhul(n-es,' ib. fj, pass from the upper to the lower jaw, and 

 directly close the mouth. Tlic openers are chiefly the mus- 

 cles, ji, which have their chief fulcrum in the coracoids, 

 and ex])and to be inserted into the .symphysis mandibular. 

 The gill-apertures arc contracted by the muscles, q, q, and di- 

 lated by others passing oljlitpicly from abo^e to their front boun- 

 daries. The muscular invest- 

 ment of the branchial chamber 

 of the Torpedo fig. 139, r, re- 

 ceives a fascicidus from the 

 scapula, and sends another, 

 \h. o, forwards to the cra- 

 nium, from which the con- 

 strictor of the electric bat- 

 tery, E, is continued. The 

 jrrntractor scapula: in the 

 Skate and Torpedo is of con- 

 siderable length, in conse- 

 quence of the backward dis- 

 placement of the scapular 

 arch, and is of great strength, 

 by reason of the enormous 

 pectoral appendage which 

 tlie arch sustains. The myo- 

 commas of the trunk are 

 fused into four great longitu- 

 dinal masses. The neuro- 

 medial mass, fig. 139, a, ^'"' 



arises from the scapula, S, and by strong carneous fasciculi 

 I'rom the vertebrre behind the scapular attachment : above the 

 pelvis they divide into tendinous slips, which pass backward 

 in separate sheaths, to be successively inserted into each vertebra 

 as far as the end of the tail. The neuro-lnteral mass or muscle, 



