CRANIAL NERVES 151 



GENERAL VISCERAL EFFERENT NERVE ROOTS 



Preganglionic fibers for unstriatcd muscles and glands leave the 

 brain in the III, VII, IX, and X roots, probably with the IV nerve 

 and its environs (p. 181) and perhaps with the parietal nerve (p. 235). 

 In other vertebrates, fibers of this system have been described as 

 leaving the brain with the optic nerve, with the nervus terminalis, 

 and independently from other regions of the brain for the meninges. 

 Our material is inadequate to reveal satisfactorily either the central 

 connections or the peripheral courses of any of these fibers, so that 

 this topic remains to be clarified. The large unmyelinated hy- 

 pophysial nerve belongs in this system, as described on page 244. 



SPECIAL VISCERAL iMOTOR NERVE ROOTS 



The striated muscles related with the visceral skeleton of the head 

 — jaws, hyoid, branchial arches, and their derivatives in higher ani- 

 mals — belong in a special category (p. 69). These muscles are vis- 

 ceral in phylogenetic and embryologic origin and primitively in func- 

 tion, but in all craniate Chordata they have acquired the same 

 striated structure as somatic muscles, as well as various degrees of 

 somatic function. They occupy, accordingly, an ambiguous position 

 and are sometimes termed "special somatic muscles" ('22, '43). Their 

 innervation is of similarly intermediate character. In Amblystoma 

 these motor fibers are thick and well myelinated and arise from large 

 cells of motor type which are more or less clearly segregated in 

 separate nuclei. These nuclei lie laterally of the somatic motor nuclei 

 and well separated from them. 



This system of fibers is represented in the V, VII, IX, and X pairs 

 of cranial nerves. Their peripheral distribution has been described by 

 Coghill ('02). Their large motor nuclei are imbedded in the tegmental 

 gray, with no clear boundaries. Their approximate positions in the 

 larva are shown as projected upon the floor of the fourth ventricle in 

 1914«, figure 1; but, as seen in other figures of that paper, their 

 dendrites ramify widely among those of the tegmental neurons. This 

 indicates that both kinds of cells are activated from the same sources. 



The motor V nucleus lies more laterally than the other members of 

 this group. A Golgi impregnation of three of its elements is shown in 

 figure 40. From it two roots arise, one from its posterior end and one 

 farther forward. There are two well-separated motor nuclei and roots 

 of the VII nerve, the roots emerging ventrally of the VIII root. The 



