Motor System — Muscles and Skeleton 



LEVATORES ARCUORUM (1-7) 



97 



HYOLARYNGEI 



HYOPHARYNGEI 



Fig. 95. Diagrams illustrating the hypothetic evolution of the hranchiomeric 

 muscles. (A) Hypothetic ancestral form. (B) Branchiomeric muscles in urodele 

 amphibian. (Redrawn after Wilder: "History of the Human Body," New York, 

 Henry Holt & Co., Inc.) 



gestive tube. Their origin from unsegmented mesoderm does not neces- 

 sarily make them "visceral." It has already been mentioned that un- 

 segmented mesoderm of the trunk may contribute to formation of ap- 

 pendicular muscles. This mesoderm in the region of the coelom produces 

 somatic (parietal) as well as visceral peritoneum, and the coelom puts 

 a wide anatomic gap between visceral and somatic muscles. In the 

 pharyngeal region there is no coelom, except transitory embryonic 

 vestiges of it. In the absence of a coelomic space, the muscles in ques- 

 tion may just as well be regarded as belonging to the body-wall as to 

 the digestive tube, and structurally they are like somatic muscles. If 

 they are assigned to the inner tube, a large part of the anterior lateral 

 region of a fish is left with no body-wall except the skin. 



These muscles of the jaws and respiratory region are still commonly 



