MORPHOGENESIS OF MUSCULAR SYSTEM 



719 



NUCHAL PORTION OF PLATYSMA AND 

 POSTAURICULO-OCCIPITAL MUSCLE GROUP 



ZYGOMATICUS 

 ZYGOMATICUS 



M. TRIANGULARIS 

 M. PLATYSMA 



Fig. 330. Facial and cervical muscles in mammals derived from the mesoderm of the 

 hyoid arch. (Redrawn from Huber, 1930, Quart. Rev. Biol., 5.) (A) Opossum (Didel- 

 phys). (B) Cat (Felis). (C) New-born baby (white) human. (D) Adult (white) 

 human. 



fold arose as a support for the fold in a manner similar to the median fins. 

 The latter theory has the greatest number of adherents today. 



The early development of the rudiments of the paired appendages and the 

 properties of the limb field are discussed in Chapter 10, page 508. Relative 

 to the developing limb; the exact origin of the cells which go to make up its 

 intrinsic musculature has been the object of much study. In the elasmobranch 

 and teleost fishes, muscle buds from the myotomes in the vicinity of the 

 developing fin fold unquestionably contribute dorsal and ventral premuscle 

 masses of cells to the limb, which give origin respectively to 



1 ) the dorsal, elevator and extensor muscles, and 



2) the ventral depressor and adductor muscles of the fin. 



