MUSCULAR SYSTEM. 



origin (biceps, triceps, etc.) ; 

 one or several points of inser- 

 tion (pinnate, bipinnate, ser- 

 rate, etc.). 



In the fish-like vertebrates 

 the trunk muscles clearly show 

 their myotomic origin, for myo- 

 tomes and the intervening myo- 

 commata are strikingly in evi- 

 dence. Even here there is a 

 tendency toward specialization, 

 for a horizontal connective tis- 

 sue partition divides the muscles 

 of each half of the body into 

 dorsal and ventral portions (p. 

 109) ; while in the ventral region 

 occurs a subdivision into a me- 

 dian rectus muscle, and a more 

 lateral oblique muscle (the 

 names being indicative of the 

 direction of the muscle fibres). 

 These same features can be 

 traced more or less clearly in 

 the higher vertebrates, compli- 

 cations being introduced by the 

 greater development of those 

 muscles which, while having 

 their origin on the trunk, serve 

 to move the limbs, and by the 

 subdivision of the others, into 

 distinct regions. Thus the rec- 

 tus may be divided into a rectus FIG. 123. 

 abdominis, extending from the of Necturus. 



ceps ; C,cora 

 cobrachialis ; 



ceratohyoid ; EO, external oblique; F, flexor communis; FC, 

 gracilis; GH, geniohyoid; 1C, ileocaudalis; LA, linea alba; 

 mylohyoid ; MO, middle oblique ; P, pectoralis ; PC, procoracoid ; 

 PH, procoracohumeralis ; PT, pectineus ; PY, pyriformis ; RA 

 RI, rectus internus ; SC, supracoracoid ; SH, sternohyoid ; VI, 



Ventral muscles 

 A, anus ; B, bi- 

 coid ; CB, cora- 

 ECH, external 

 femorocaudalis; G 



AT, masseter ; MH, 



PF, pubofemoralis ; 



, rectus abdominis ; 



vastus internus. 



