THE NERVOUS SYSTEM. 



495 



the nuclei of the XII, VI, IV and III cranial nerves, and their axones grow 

 out as medial ventral root fibers (except the IV) (Fig. 427) to the differenti- 

 ating muscles of the tongue and eyeball which they respectively innervate. 

 These muscles are probably somatic and their nerves are the somatic efferent 

 cranial nerves corresponding with the greater part of the fibers of the ventral 

 roots of the cord (compare p. 469) . The lateral series consists of the nuclei of 

 the efferent portions of the roots of the XI, X, IX, VII and V cranial nerves 

 and their axones grow out as lateral roots (Fig. 427) to the differentiating 

 striated branchial (splanchnic) muscles (sternocleidomastoideus, trapezius, 



FIG. 428. Diagram of the floor of the 4th ventricle of a 10 mm. human embryo, illustrating the 

 rhombic grooves and their relations to the cranial nerves. The point of attachment of the 

 acoustic and the sensory root of the trigeminal nerve is shown by dotted circles; the motor 

 nuclei are represented by heavy dots. Streeter. 



pharynx, larynx, face and jaw) and also to muscles of the viscera (via sympa- 

 thetic?). The lateral nuclei and their roots are thus splanchnic. (Cp. pp. 

 302-3, 469, 471.) Their root fibers, with the incoming afferent fibers, form the 

 mixed roots of these nerves. The positions of these various nuclei and their 

 roots are clearly indicated in Figs. 427, 436-439, 447 and 451 and require no 

 further description. Additional details are mentioned in connection with 

 the afferent cranial nerves. In the region of the vagus nerve, there are 

 differentiated two series of lateral nuclei, a ventro-lateral (nucleus ambiguus X) 

 and a dorso-lateral (dorsal efferent nucleus X} (comp. Fig. 407). Fig. 452 

 32 



