496 



THE MUSCULAR SYSTEM. 



subject, it appears certain that at least two series of elementary structures are concerned 

 in the formation of the muscles of the head and face the cephalic myotomes and the 

 muscular structure of the branchial arches. 



The number of myotomes originally existing in the region of the head is not known, 

 although it is stated with some authority that nine is the complete number. The first three 

 are described as persisting in the form of the ocular muscles, the last three in relation to 

 the muscles of the tongue, while the three intervening myotomes disappear. 





FIG. 438. SCHEME TO ILLUSTRATE THE DISPOSITION OF THE MYOTOMES IN THE EMBRYO IN RELATK 



THE HEAD, TRUNK, AND LIMBS. 



A, B, C, First three cephalic myotomes ; N, 1, 2, 3, 4, Last persisting cephalic myotomes ; C., T., L., S., Co 

 The myotomes of the cervical, thoracic, lumbar, sacral, and caudal regions ; I., II., III., IV., V., VI 

 VII., VIII., IX., X., XL, XII. , refer to the cerebral nerves and the structures with which they may T 

 embryologically associated. ^ 



The following table shows the possible fate of the cephalic myotomes : 



First, Superior, medial and inferior recti, obliquus inferior, levator palpebrse superioris. 



Second, Obliquus superior. 



Third, Rectus lateralis. 



Fourth, Fifth and Sixth, Absent. 



Seventh, \ 



Eighth, ^Muscles of the tongue. 



Ninth, i Muscles connecting the cranium and shoulder girdle. 



Tenth (first cervical) J 



The mesoblastic tissue of the branchial arches is probably concerned in the production 

 the following muscles of the face and neck : 



First (mandibular) arch . . . Muscles of mastication. 



[Platysma and facial muscles. 

 Second (hyoid) arch -j Muscles of the soft palate. 



I Stapedius, stylo-hyoid, and digastric. 



Tk M (tkyreo-kyoid) arcH 



Four* on* FiftK M Z) a rc hes 



