THE MAMMALIAN NERVOUS SYSTEM 77 



In connection with this section read Herrick ('18), Chap. 

 XVII, and Johnston ('06), Chap. IX. 



85. The organs of taste. If microscopic material showing 

 the structure of the taste-buds is available it should be exam- 

 ined in connection with the study of the visceral sensory 

 system (see Bailey ('16), pp. 229-232, 593; Cunningham ('15), 

 pp. 854-856; Piersol ('16), Figs. 1193-1197). There has been 

 much dispute among neurologists regarding the nerve-roots by 

 which taste-fibers reach the brain. The student should be- 

 come familiar with the various theories (see Gushing ('03), 

 Herrick ('18), Fig. 115, and the accompanying discussion). 



86. Visceral efferent system. In the microscopic sections 

 identify and draw the dorsal motor X nucleus under the ala 

 cinerea. See Section 62 (4) and Herrick ('18), Figs. 71 to 74 

 and 114. This is the general visceral efferent nucleus of the 

 vagus. The general visceral efferent nuclei of the IX and VII 

 nerves are respectively the inferior and superior salivatory 

 nuclei (see Herrick ('18), Figs. 71, 73, and 114). These are 

 not easily identified in the sections. Identify also the nucleus 

 ambiguus (Herrick ('18), Figs. 71 to 74 and 114) and the chief 

 motor nuclei of the VII and V nerves. These are the nuclei 

 of the special visceral motor components. Look for fibers 

 passing out from them into the V, VII, IX, and X nerves. 

 Extending from the nucleus ambiguus downward into the 

 spinal cord is the nucleus of the XI nerve. In the upper levels 

 of the cervical cord these cells form the lateral gray column. 

 Fibers may be seen passing directly lateralward from this nu- 

 cleus into the spinal roots of the XI nerve. 



Sections of the midbrain through the nucleus of the III nerve 

 will show a median group of cells of this nucleus, the nucleus 

 of Edinger-Westphal (see Herrick ( r !8), Fig. 71) which sends 

 general visceral efferent fibers to the ciliary ganglion. 



Visceral reflexes may be effected by short and very simple 

 connections between the afferent visceral sensory fibers termin- 

 ating in the nucleus of the fasciculus solitarius and the efferent 

 visceral fibers arising from the motor nuclei mentioned in the 

 preceding paragraphs. The neurons of the nucleus of the 

 fasciculus solitarius serve to connect these primary centers (see 

 Herrick ('18), Fig. 113). On the visceral efferent system in 

 general, see Johnston ('06), Chap. XII, 



