718 THE MUSCULAR SYSTEM 



represents superficial facial musculature, and the M. depressor mandibulae 

 or deep facial musculature. In mammals (figs. 327E'; 330A-D), the muscles 

 derived from the hyoid arch is distributed over the cervico-facial area as many 

 separate muscles. The musculature derived from the hyoid arch is innervated 

 by the seventh or facial cranial nerve. Reference may be made to the extensive 

 review of the literature by Huber ('30, a and b), relative to the facial 

 musculature in vertebrates. 



d) Musculature of the First Branchial Arch. The musculature of 

 the first branchial arch is innervated by the glossopharyngeal or ninth cranial 

 nerve. In the shark, the muscle tissue arising from the first branchial arch 

 becomes the constrictor musculature of this arch, but, in the mammal, it 

 gives origin to the stylopharyngeus muscle and to the constrictors of the 

 pharynx. 



e) Muscles of the Succeeding Visceral Arches. In the shark, these 

 muscles contribute to the constrictor muscles of the gill arches and are under 

 the domain of the vagus or tenth cranial nerve. In the mammal, this muscle 

 tissue becomes associated with the larynx and with the constrictors of the 

 pharynx. 



f) Muscles Associated with the Spinal Accessory or Eleventh 

 Cranial Nerve. The sternocleidomastoid and trapezius musculature in the 

 human, according to W. H. Lewis ('10), arises from a premuscle mass as- 

 sociated at the caudal end of the pharyngeal area below the post-otic myo- 

 tomes (fig. 336A). With the musculature arising from this premuscle mass, 

 the spinal accessory or eleventh cranial nerve becomes associated. The tra- 

 pezius musculature migrates extensively over the scapular area (fig. 329A). 



g) Musculature of the Mammalian Diaphragm. The striated mus- 

 culature of the mammalian diaphragm appears to arise from the ventral por- 

 tions of the myotomes in the midcervical area. In the human, this diaphragmatic 

 musculature is innervated by the ventral roots of cervical nerves IV and V, 

 while, in the cat, cervical nerves V and VI are involved. These ventral rami 

 give origin to the phrenic nerve, which later migrates posteriad with the 

 diaphragmatic musculature together with the developing diaphragm during 

 the division of the coelomic cavities (Chap. 20). 



c. Development of the Musculature of the Paired Appendages 



Two main theories have arisen relative to the origin of the paired append- 

 ages. One is the gill-arch theory of Gegenbauer (1876) and the fin-fold or 

 lateral-fold theory of Balfour ( 1881 ). According to the theory of Gegenbauer, 

 the limb girdles are modified gill arches, and the limb tissue itself represents 

 a modification of the gill septa and supporting gill rays. The pelvic limbs were 

 produced, according to this theory, by a backward migration of the gill arch 

 involved. The lateral-fold theory, on the other hand, postulated that the paired 

 hmbs were derived from longitudinal fin folds. The endoskeleton within the 



