636 'Journal of Comparative Neurology and Psychology. 



complex as one nerve, representing the conjoined trunks of several 

 segmental nerves. This complex contains all the components 

 (fig. 9, diag. B); the tv^^o sensory components run with the vagus 

 to the ganglia found on the root and in a chain extending back- 

 ward. Sometimes the caudal fibers run to caudal ganglia, Fro- 

 RiEP's or hypoglossal ganglia, by way of the hypoglossal trunk 

 which they join where it crosses the vagus. Of the motor com- 

 ponents, all three are present; the ventro-mesial efferent runs as 

 the hypoglossal nerve to the muscles of the tongue, derived from 

 the ventro-mesial cells of the myotomesof correspondingsegments; 

 the ventro-lateral efi^erent fibers run in the accessory nerve, and 

 after junction with the other components, as in a spinal nerve, 

 turn dorsally like a dorsal ramus, and innervate one of the muscles 

 of the back, namely the trapezius, joining often with the dorsal 

 rami of the upper cervical nerves; or turn ventrally, Hke the nerves 

 to the limbs, and innervate the sterno-mastoid, one of the muscles 

 connected with the shoulder girdle, overlying the body muscles, 

 and hence to be classed as a limb muscle. The third motorcompo- 

 nent, the visceral efferent, is represented bytherest of the accessory 

 nerve and the motor fibers of the vagus, and consists of two varie- 

 ties of fibers. Running chiefly with the accessory root, but join- 

 ing the vagus trunk later, are visceral efferent fibers like those in 

 the cord (except for their lateral exit from the medulla) which pass 

 to sympathetic ganglia of the stomach, lungs, heart, etc., and 

 innervate indirectly the involuntary muscles derived from the 

 median part of the coelom (lateral mesoderm); while the true 

 vagus fibers, also visceral efferents, innervate directly, without the 

 intervention of sympathetic ganglia, the striated muscles of the 

 oesophagus, pharynx and larynx. The vaso-motor and glandular 

 fibers are mingled with both of these varieties, completing the 

 visceral efferent component. All of the components, then, are 

 present. 



The difference between this conception of the vago-accessory- 

 hypoglossal complex and that of Johnston is the addition of a 

 somatic motor component, running in the lateral root, and inner- 

 vating myotomic muscles, "typical body muscles." It places 

 the trapezius muscle and the sterno-mastoid on a par with similar 

 muscles of the lower limb; it explains the junction of the accessory 

 fibers with the dorsal rami of the cervical nerves. Moreover, it 

 is borne out by the conditions found in birds and reptiles, where, 



