272 



COMPARATIVE ANATOMY 



trunk muscles become relatively reduced. Subdivision and migration of 

 muscles increases. Caudal muscles dwindle with the reduction of the tail. 

 In the trunk region, metamerism is preserved only in the intercostals, 

 the rectus abdominis, and the intervertebral muscles. 



Integumental (Dermal or Cutaneous) muscles in the form of a panni- 

 culus carnosus group appear suddenly in monotremes and marsupials 

 only to disappear in the higher primates except as rudiments. In the 



-M. PIRIFORMIS 



ABDUCTOR CAUDAE VENT. 



M. EXTENSOR CAUDAE 

 LATERALIS 



M. ABDUCTOR CAUDAE 

 DORSALIS 



B. DORSAL 



Fig. 226. — Human caudal muscles viewed from A. ventral and B. dorsal side. 

 These rudimentary muscles are the last remnants of the powerful caudal muscles of the 

 lower vertebrates. The presence of such useless rudiments receives its best interpreta- 

 tion in the evolution theory. (Redrawn from Wilder's " History of the Human Body," 

 Henry Holt & Co.; after Lartschneider.) 



head and neck region, however, the platysma and facial muscles persist 

 in man and apes. In the trunk region, these integumental muscles are 

 outgrowths of the pectoralis minor complex. In the head region, however, 

 they are visceral in origin. 



The most important muscular novelty contributed by mammals is the 

 diaphragm. Its innervation by branches of cervical spinal nerves proves 

 that it is a derivative of cervical myotomes. 



There is no essential difference between the muscles of man and those 

 of other mammals. The presence in man of such useless muscle rudi- 

 ments as the sacro-coccygeal and ear muscles suggest a mammalian 



