58 ANNALS NEW YORK ACADEMY OF SCIENCES 



probably a muscle with a double origin, since it originally has two bellies, 

 the anterior innervated by the fifth nerve and the posterior belly by the 

 seventh. 



In spite of some seeming contradictions, the nerves offer the best means 

 of determining homologies in the muscles. Wilder (1909, p. 196) says: 



Were it possible to follow each motor nerve fiber from its origin to its con- 

 nection with its muscle, it would probably serve as an absolute criterion for 

 muscular homology, but there is a chance for error in the fact that an ana- 

 tomical nerve is not a single fiber, but a bundle of them, and while each fiber 

 is presumably constant in its supply, there is some variation in the way in 

 which they are put into bundles, so that no one can be sure that a given nerve 

 is quite homologous with one in a like location in another animal. 



Most anatomists agree with Wilder's statement of the case. We may 

 suppose that these changes of the contents of the bundle are responsible 

 for some of the examples of apparent non-homology that often occur in 

 animals that are closely related. We may assume that in the original 

 condition of the vertebrates the myotomes were placed in regular order 

 and each myotome was supplied with a serial nerve. With the gradual 

 changes that took place in development the higher vertebrates disguised 

 the metameric arrangement until only slight remnants of them remain 

 in a few muscles like the obliquus externus of man; The myotomes are 

 evident through the fishes and tailed amphibians, but are not so evident 

 in the reptiles and mammals. The elements of certain of the myotomes 

 usurped the position of the others and developed into the larger muscles 

 of the trunk, carrying with them their original nerves, thereby destroying 

 the primitive arrangement. 



In a paper by D. J. Cunningham (1891) the problem of nerve and 

 muscle is very carefully considered. He considers the nerve supply a 

 good guide but not an infallible one. He says that a solution of the 

 problem can only be obtained by approaching the question from two 

 points of view: first, by studying the early connections which exist be- 

 tween the nervous and the muscular system in the embryo; second, by 

 examining one or more groups of muscles, the homologies of which are 

 undoubted, in a large series of animals or in a large number of indi- 

 viduals of the same species, and observing whether in every case the nerves 

 of supply are the same. 



In many cases the nerves are found fusing into a plexus. Cunning- 

 ham's paper favors the view that the same ganglion cells are invariably 

 connected with the same muscle fibers, but that the fibers may adopt a 

 different path and thus reach their connection through another route. 

 This seems incapable of proof, but it is a good working hypothesis. He 



