320 THE MORPHOGENESIS OF THE SKELETON AND MUSCLES 



larly the 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 therefore it 

 has been assumed that they are derived from myotomes of the occipital region. 

 According to Lewis, "there is no evidence whatever for this statement, and we are 

 inclined to believe from our studies that the tongue musciilature 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 develop- 

 mental factors listed on p. 317. 



