396 



Bashford Dean Memorial Volume 



THE BRANCHIOMERIC MUSCLES 



The segmentation that gives rise to the branchial arches is of a different nature from 

 that which carves out the somites. The term branchial arches is used by embryologists, 

 in its voidest sense, to include the mandibular and hyoid arches which are considered 

 to be modified gill-arches. By comparative anatomists, the entire series is usually designat- 

 ed the visceral skeleton, and the arches are called visceral arches. It is common to speak 

 of the branchiomeric muscles as the pharyngeal muscles, here also making no distinction 

 between mouth and pharynx. 



superficiai co?7str/dor 

 Tnuscles of^i/larches 



nerire 



eyemuscles 



lafeml 

 cana/s 



adduclor muscles 

 ofjaii/s 



MecMs 

 cartilage 



Text-figure 70. 



A dissected head of C\i\am-^iosdac\iu& ang\xme.us in lateral view. 



From Gregory, 1933, Fig. 6; redrawn and slightly simplified after color figure in AlKs, 1923, pi. IV. 



'/■z.'in/r' 



While the metameric muscles are derived, at least in large part, from a dorsal zone 

 of early mesoderm which has previously been cut up into somites, the muscles of the 

 branchial (visceral) arches (excluding the hypobranchial group of muscles) do not arise 

 from somites but from mesoderm that is commonly regarded as splanchnic. The nerves 

 that supply these muscles are placed in a different category (visceral) from those (somatic) 

 that supply metameric muscles. 



Fiirbringer (1903) described some of the muscles of gill-arch origin, particularly 

 those of the mandibular arch, in C\Aam-^d.oselac}ms. Luther (1909) described the muscles 

 innervated by the trigeminal nerve. Goodey (1910.1) described the muscles of the 

 mandibular and hyoid arches. AUis (1923) has given a detailed, comprehensive and 

 beautifully illustrated description of the pharyngeal muscles of Chlam^idoseldcfius, which 



