THE MAMMALIAN NERVOUS SYSTEM 69 



which have now been analyzed comprise the spinal V tract and 

 its nucleus, the chief sensory V nucleus, the mesencephalic V 

 tract and nucleus, the dorsal funiculi and medial lemniscus, and 

 the spinal lemniscus. The centers mentioned receive all fibers 

 of cutaneous and deep sensibility from the head, trunk, and 

 limbs except those serving the muscle-sense from the extrinsic 

 eye-muscles. Fibers of this character are present in the III, 

 IV, and VI cranial nerves, but of their central connections 

 nothing is known. 



From these primary sensory centers connections are made 

 through the reticular formation (see Section 89) with neighboring 

 motor centers for local reflexes. All ascending tracts of the 

 second order from the primary sensory centers to the thalamus 

 are termed lemnisci. The trigeminal lemniscus and the spinal 

 lemniscus carry exteroceptive nervous impulses (general somatic 

 sensory series). Proprioceptive reactions are served by (1) 

 the dorsal funiculi of the cord and medial lemniscus, (2) vestibu- 

 lar system, and (3) the cerebellar connections. The first of 

 these three belongs in the general somatic sensory series, the 

 second in the special somatic sensory series, while the cere- 

 bellum is the general co-ordination center for both of these 

 series. 



The papers of Head and his associates (see Head and Thomp- 

 son ('06), and Head and Holmes ('11)) may profitably be read 

 at this time; also Johnston ('06), Chapter VI. 



80. Organ of hearing. — If microscopic sections are available, 

 study the cochlea and spiral organ (organ of Corti). Accounts 

 of the structure and functioning of the internal ear may be 

 found in most of the standard text-books. See Bailey ('16), 

 pp. 580-590; Cunningham ('15), pp. 843-854; Herrick (15), 

 Chap. XIII; Howell (15), Chap. XX, pp. 385-403; Morris (14), 

 pp. 1092-1096; Starling (12), pp. 569-577; Stewart (14), pp. 

 1024-1035. For special reference, the literature cited at the 

 end of chapter XIII (Herrick, 15) is recommended, particu- 

 larly the papers of Hardesty ('08a) and (15), Prentiss (13), and 

 Shambaugh ('07) and ('08). 



81. Gross preparation of the cochlear nerve and its connections. — 

 In the gross specimens locate the inferior peduncle of the cere- 

 bellum (corpus restiforme), which connects the dorso-lateral. 



