MUSCULATURE 



The muscles of Necturus are characteristic of those in 

 the Urodeles, in that they show many fishlike adaptations. 

 The body muscles are divided into myotomes which are 

 separated by myocommata. In the higher vertebrates this 

 primitive arrangement is lost or can be seen only in such in- 

 stances as the tendinous inscriptions and in some of the 

 back muscles. Muscles are used to move various parts of 

 the body and therefore each muscle has a place of origin 

 and insertion. Usually the origin is on a fixed element 

 while the insertion is on a part to be moved. Sometimes 

 both the origin and insertion are on movable parts but in- 

 stances of this are rare in skeletal muscles. Muscles are 

 usually inserted on bone or connective tissue but some 

 instances are found where insertions are on other muscles. 



Muscles usually work in pairs since muscle fibers can do 

 nothing but contract. To return to its original position, 

 a second muscle is required to keep the muscular balance. 

 The names used in this guide are for the most part those 

 that indicate the nature of the work that the muscle per- 

 forms. Names used in human anatomy have been avoided 

 since the homology of the muscles in the Urodeles is 

 uncertain. 



The muscles of the limbs are often fusiform since this 

 type takes up less bulk for the amount of muscular tissue 

 involved. Triangular muscles appear where there are 

 narrow origins and broad insertions, such as is found in the 

 pectoralis or in some of the muscles attached to flat bones 

 like the scapula. Sheet muscles appear in the diaphram 

 where a solid sheet of uniform thickness is needed. 



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