720 



THE MUSCULAR SYSTEM 



In tetrapod vertebrates, however, the exact origin of the cells which enter 

 into the formation of the limb's intrinsic musculature is open to question. In 

 the amphibia, including Urodela and Aniira, Field (1894) described myo- 

 tomic processes which contribute to the musculature of the anterior limbs. 

 Byrnes (1898), working experimentally with the same group, and W. H. 

 Lewis ('10b) deny this conclusion and affirm the somatopleural or in situ 



HOMOCERCAL TYPE 



( CYPRINUS CARPIO 1 



(GERMAN CARPI 



ETEROCERCAl type 

 ^ scaphirhyncmus ) 



Fig. 331. (A) Innervation of premuscle masses in head and pharyngeal areas, and of 

 myotomes in the cervical and caudal head regions of 7-mm. human embryos. Four 

 post-otic (occipital) myotomes and the premuscle mass of the trapezius and sterno- 

 mastoid muscles are shown just back of the tenth cranial nerve. The first cervical myotome 

 and spinal nerve are shown just posterior to the fourth occipital myotome. (Redrawn from 

 W. H. Lewis, 1910, chap. 12 in Manual of Human Embryology, vol. I, by F. Keibel 

 and F. P. Mall, Philadelphia, Lippincott.) (B, C, D) Types of caudal fins in fishes. 



