66 LABORATORY OUTLINE OF NEUROLOGY 



through the large mass of the transverse pons fibers below the 



V root with a sharp knife in order to expose the spinal V fibers. 

 This dissection, however, should not be made on the same speci- 

 men which is to be used for the optional dissections of the ob- 

 longata (Sections 102-111). 



73. Microscopic study of the V roots. — In the microscopic 

 sections find the sensory V root in the pons region (see the refer- 

 ences in Section 62 (7)), and follow its fibers backward into the 

 spinal V tract. Only a part of the sensory V root-fibers enter 

 this tract. Others enter the chief sensory V nucleus, which lies 

 dorsally of the spinal V tract at the level of entrance of the fibers 

 of the V nerve and forward (rostrally) of this level. The chief 

 sensory nucleus of the V nerve and the spinal V nucleus (sub- 

 stantia gelatinosa of Rolando), which accompanies the spinal 



V tract, are the terminal nuclei of the general cutaneous com- 

 ponents of the cranial nerves. These nuclei and the spinal V 

 tract should be located and entered in the drawings of all sec- 

 tions in which they occur. 



A few general cutaneous fibers enter the spinal V tract and its 

 nucleus from the IX and X roots also, but these are usually not 

 evident in the sections. The motor nucleus of the V nerve will 

 be seen lying medially of the chief sensory V nucleus and it may 

 be drawn in at this time. Golgi sections show that some per- 

 ipheral sensory V fibers end in the motor V nucleus, thus pro- 

 viding a direct reflex connection between the skin of the face 

 and mouth and the jaw muscles. Neurons of the spinal V 

 nucleus effect the connection between the peripheral cutaneous 

 fibers of the spinal V tract and the motor nuclei of the VII, IX, 

 and X nerves. 



74. Trigeminal lemniscus. — The ascending secondary fibers 

 from the chief sensory V and spinal V nuclei to the thalamus form 

 two tracts, both of which are called the trigeminal lemniscus. 

 Their fibers cannot easily be traced in either gross or microscopic 

 preparations. 



For diagrams showing the positions of the V nuclei and their 

 connections with other centers in the brain, see Bailey ('16), 

 Fig. 344, p. 512; Herrick ('15), Figs. 64, 71, 73, 75, 77, 78, 81; 

 Morris ('14), Fig. 654, p. 828; Rauber-Kopsch ('07), Fig. 681, 

 p. 615. 



