Bremer, Aberrant Roots. 631 



that the fibers of this component change their point of exit from 

 the hne of ventral roots to the postero-lateral groove. In the 

 brain the somatic motor component is represented by the oculo- 

 motor, trochlear, abducent, and hypoglossal nerves, whose dis- 

 tribution is to muscles derived from head and occipital somites 

 while the visceral motor component is represented by the motor 

 parts of the other cranial nerves, and, beside innervating the 

 glands, heart, and blood vessels, and the smooth muscles of the 

 intestinal tract, also controls the striated muscles of the head and 

 many in the neck. He explains this peculiar segregation of these 

 special muscles from the other striated muscles of the body by their 

 embryological derivation from lateral mesoderm, instead of from 

 somites, which makes these striated muscles embryologically 

 homologous with the smooth muscles of the intestine and with 

 the heart muscle; and therefore properly supplied by the same 

 nerve component as the smooth muscles. 



But Johnston carries this further; the trapezius musculature 

 in all classes of mammals is innervated by the accessory nerve, 

 undoubtedly a lateral root nerve. The striated muscles (except 

 the heart) known to arise from lateral mesoderm, are all originally 

 in connection with the gill pouches, and so may the more justly 

 be homologized with the intestinal muscles, both being in rela- 

 tion with the epithelium of the intestinal tract. In order that the 

 trapezius may be classed in this same category, and therefore 

 justify its innervation, Johnston states that "the only probable 

 explanation is thatthe shouldergirdle or pectoral arch did not have 

 its origin as a part of the skeleton of a limb, but existed as a bran- 

 chial arch before the limb was formed;" that the musculature of 

 this girdle belonged to a posterior branchial arch, now lost, and only 

 secondarily became attached to the arm and the trunk. 



With this explanation of the innervation of the trapezius muscu- 

 lature I cannot agree. Two facts especially seem to me to militate 

 strongly against it; first, the subdivision of the lateral column of 

 gray matter into a dorsal nucleus of the glossopharyngeal and 

 vagus nerves and a more ventral nucleus ambiguus, a fact left 

 unexplained by Johnston; and second, the innervation of the 

 trapezius muscle, by the dorsal rami of the first and second cervical 

 nerves, which often anastomose with the accessory branches. If 

 this muscle is of branchial origin, why should it be innervated by 

 branches of ventral roots ^ 



