viii.] THE MUSCLES. 363 



chians, also the psoas and femoro-caudal and the muscular 

 masses investing the chevron bones of Cetaceans, and the 

 lower caudal muscles of some Fishes, e.g. the Sole. 





12 



FIG. 321. SUPERFICIAL MUSCLES OF THE PERCH. 

 The fin-rays of all the fins are cut short off. 



i, great lateral muscle, showing the numerous vertical tendinous intersections 

 slightly but variously inflected ; 2, small superficial muscles inserted into the 

 fin-rays of the dorsal and ventral fins ; 4, slender longitudinal muscle running 

 (in the interval of the summits of the two great lateral muscles) between the 

 dorsal and caudal fins; 5, similar muscle on the ventral margin, which also 

 appears between the anal and ventral fins ; 6, small radiating muscles of the 

 caudal fin ; 7, part of the great lateral muscle inserted into the skull ; 8 and 9, 

 elevators of the operculum ; 10, elevator of the palato quadrate arch ; n and 

 12, muscular mass which by its contraction closes the jaws ; 13, superficial 

 muscles of the pectoral fin ; 14 and 15, muscles of the ventral fin. 



The muscles which invest that special division of the 

 hypaxial skeleton, the splanchnapophyses, also constitute a 

 group by themselves, connecting together the hyo-branchial 

 arches and the jaws, the stylo-hyoid, constrictors of the 

 pharynx, buccinator, c. 



The appendicular muscles may be divided into those of the 

 limb-girdles and those of the appended limb. 



They may be at a maximum of size in relation to the axial 

 system, but simple and without any special differentiations, 

 as in the Rays. They may be at their maximum of dif- 

 ferentiation, though less in relative or even in absolute size, 

 as in the highest Mammals. 



This differentiation begins to be indicated directly weascend 

 from the class of Fishes, as we have seen that even in the 

 Tailed-Batrachians definite flexors, extensors, pro- and su- 

 pinators already appear ; and these distinctions, once esta- 

 blished, persist' up to man himself, though with increasing 

 complications. Special complications, especially of the 

 muscles of the pelvic limb, have been found by us to be 

 developed in Reptiles, such as we do not find in man's 

 own class. 



