Motor System — Muscles and Skeleton 



99 



Lower jaw-I 



Hyoid IE 



Coracomandibular 

 Geniohyoid 



Sternohyoid 



Coracohyoid 



Thyrohyoid 

 Sternothyroid 



Coracobranchials 



^Tongue 



^v^.Genioglossus 

 "^v /Hyoglossus 



» Stylohyoid ligament 



— Hyoid n+m 



Pectoral girdle 



Fig. 97. Diagrammatic representation of the hypobranchial muscles. (A) Shark 

 ventral view. (B) Mammal: left side view. 



of the skin (Fig. 96). Even the trapezius, an extensive and important 

 superficial dorsal muscle of the pectoral appendage, has, at least 

 in part, been assigned to this group. To call the human facial 

 muscles "visceral" seems a perversion of the term. " Branchiomeric " 

 relieves the vertebrate of the embarrassment of having numerous vis- 

 ceral parts externally exposed. 



HYPOBRANCHIAL MUSCLES 



These are ventral muscles which, in fishes, extend longitudinally 

 forward from the pectoral girdle and are attached in various ways to 

 the ventral parts of the several skeletal arches of the pharyngeal re- 

 gion and to the lower jaw (Fig. 97). Although situated in close relation 

 to the branchiomeric muscles, the hypobranchial muscles are typi- 

 cally somatic. They are produced by extension of several embryonic 

 myotomes downward and forward (Fig. 92A), and retain traces of their 

 segmental origin. Judging by embryonic origin and innervation, these 

 hypobranchial muscles of the fish correspond to certain ventral muscles 

 (hypoglossal) of the throat and muscles of the tongue in higher 

 vertebrates. 



EYE-MUSCLES 



The eyeball is moved in its orbit by six muscles (described in the 

 account of the cranial nerves on p. 162). These are striated voluntary 

 muscles innervated by cranial nerves. They are derived from the most 

 anterior three pairs of myotomes of the embryo (Fig. 5). They must 



