320 THE MORPHOGENESIS OF THE SKELETON AND MUSCLES 



muscles of expression, and other muscles supplied by the facial nerve, 

 originate from the second, or hyoid arch. The third arch probably gives 

 origin to the pharyngeal muscles, and the third and fourth arches to the 

 intrinsic muscles of the larynx. 



The muscles of the tongue are supplied by the n.hypoglossus, and there- 

 fore it has been assumed that they are derived from myotomes of the 

 occipital region (p. 153). According to Lewis, "there is, however, no direct 

 evidence whatever for this statement, and we are inclined to believe from 

 our studies that the tongue musculature is derived from the mesoderm of 

 the floor of the mouth." 



Anomalies. Variations in the form, position, and attachments of the muscles are 

 common. Most of these anomalies are referable to the variable action of the several 

 developmental factors listed on p. 317). 



