EMBRYOLOGICAL DEVELOPMENT The embryological origin 

 of the limb muscles gives an insight into their functional 

 differentiation. The musculature of the mammal arises as 

 dorsal (extensor) and ventral (flexor) condensations of mes- 

 enchyme in the limb bud. Table 14-2 indicates the progres- 

 sive modification of these masses in the pectoral limb into 

 proximal, forearm, and hand segments and the separate 

 components of the proximal mass. 



The phylogeny of the scapular muscles of the placental 

 mammal is indicated by their ontogeny in the opossum. In 

 Echidna or the reptile the supracoracoideus muscle is a 

 unit, just as it is in the early developmental stages of the 



opossum (Figure 14-11). In the latter the single muscle 

 grows backward and upward, bifurcates at the spine of the 

 scapula to become the supra and infraspinatus muscles. The 

 embryology of other muscles indicates changes in shape, 

 number of parts, and even origin and insertion. Circuitous 

 routes of innervating nerves are observed to be the result of 

 migration of the muscle. 



INNERVATION Another aspect of myology which has been 

 emphasized concerns innervation, the identification of the 

 nerve serving each muscle and the constancy of this rela- 

 tionship in the several classes. Much of the past discussion 



tibialis anterior. 



gastrocnemius caput medialis 



.gastrocnemius caput lateralis 



extensor digitorum longus 



—soleus 

 peroneus longus 

 peroneus tertius 

 peroneus brevis 



popliteus 



tibialis anterior 

 flexor hallucis longus 



flexor digitorum longus 

 tibialis posterior 



gastrocnemius caput medialis 



B 



gastrocnemius 

 caput lateralis 



soleus 



flexor digitorum longus 



tibialis posterior 

 peroneus longus ^ "^ ' -'^ \^ //-' 



peroneus tertius^3^|_^^''~--tibiolis anterior 



peroneus brevis |^,ensor digitorum longus 



fibula 



Figure 14-10. Muscles of the shank of the cat. A, outer muscles; B, inner muscles; C, deeper de- 

 tails of B. 



SKELETAL MUSCULATURE 



431 



