THE MORPHOGENESIS OF THE SKELETON AND MUSCLES 



of the body wall. If they persist at all, it is possible that they contribute 

 to the formation of the lower limb. The ventral portions of the third and 

 fourth sacral myotomes give rise to the muscles of the perineal region. 



Muscles of the Limbs. It has generally been believed that the muscles 

 of the extremities are developed from buds of the myotomes which grow 



FIG. 322. Reconstruction of a 9 mm. embryo, to show the partially fused myotomes and 

 the premuscle masses of the limbs (Bardeen and Lewis). X 13. Distally, in the upper ex- 

 tremity, the radius, ulna and hand plate are disclosed; in the lower extremity the os coxas and 

 the border vein show. 



into the limb anlages. In sharks this is clearly the case, and in man the 

 segmental nerve supply is suggestive, but not proof, of a myotomic origin. 

 According to Lewis, "there are no observations of distinct myotome buds 

 extending into the limbs" in man. Nevertheless, a diffuse migration of 

 cells from the ventral portion of the myotomes has been recorded by va- 



