Bremer, Aberrant Roots. 635 



Johnston's somatic efferent component comprises the remain- 

 ing two columns of cells, whose axons innervate the body muscles. 

 This I have divided into two components, the ventro-mesial and the 

 ventro-lateral, corresponding to the two columns of cells. Recent 

 investigation, summed up by Santee, points to the fact that the 

 ventro-mesial cells innervate the ventral trunk muscles, derived 

 from the ventral part of the myotomes, the enlargement of the 

 column at the lower cervical segments being due to the large phrenic 

 nerve which innervates a muscle also derived from the same part 

 of the myotomes. This is the proposed ventro-medial component. 



The increase of the ventro-lateral column (2) at the cervical and 

 lumbar enlargements points to the fact that these cells control the 

 muscles of arm and leg, while its continuity throughout the cord 

 points to its control of a smaller body of muscles continuous 

 throughout the trunk, namely, according to this theory — the back 

 muscles. This ventro-lateral component, then, controls the mus- 

 cles of the back and those of the limbs, which are here consid- 

 ered homologous,' and turns laterally from the main nerve trunk 

 either as a dorsal ramus, or as a branch to the limb. This is not 

 without proof, for Lapinsky's tables agree remarkably well with 

 this conception. 



In the medulla oblongata the visceral efferent component takes 

 a new direction, as shown by Johnston, and becomes a lateral 

 root; the ventro-mesial component retains its ventral position, and 

 is represented by the hypoglossal nerve and the eye-muscle nerves; 

 while the ventro-lateral component becomes a lateral root. Two 

 components, then, become lateral, one remains ventral; the nuclei 

 of origin correspond exactly. The nuclei of the hypoglossal 

 nerve and of the eye muscle nerves are median, though no longer 

 ventral, having been forced dorsally by the accumulations of 

 fibers from the motor and sensory decussations; the nucleus of the 

 ventro-lateral component is represented by the nucleus ambiguus; 

 while the nucleus of the visceral efferent component is the dorsal 

 nucleus of the glossopharyngeal, vagus and accessory nerves, and 

 the other motor nuclei in the floor of the IV ventricle. The rela- 

 tive positions of the three columns of gray matter in the cord are 

 maintained, if we consider the opening of the medulla and the 

 changes of fiber tracts. 



Let us now see how this theory will account for the cranial 

 nerves; and here we shall consider the vagus-accessory-hypoglossal 



