482 THE ORGANS 



muscles of tongue (XII) and eye (VI, IV and III). Nerve III also 

 contains splanchnic neurones whose axones pass to sympathetic 

 ganglia (ciliary). Nerves III, IV and VI probably also contain 

 afferent nerve fibres (p. 480, (2)). 



Intrasegmental and Intersegmental Neurones. — These are 

 represented principally by the gray reticular formation of the 

 hindbrain and midbrain and long descending tracts external to it. 

 The gray reticular formation is composed of neurone bodies and short 

 intersegmental tracts intermingled. Among the former are certain 

 well differentiated nuclei (e.g., nucleus ruber, nucleus of Deiters, 

 and nucleus of the medial longitudinal fasciculus) the axones of 

 which form long, principally descending, intersegmental tracts 

 external to the gray reticular formation. These may also be links 

 in efferent suprasegmental paths. (See also pp. 483-4, XIV, XVI, 

 XVII and XVIII.) Other cells in the gray reticular formation form 

 the shorter tracts within it. The reticular formation may also con- 

 tain motor nuclei of the cranial nerves and is traversed by various 

 fibres passing to tracts and by terminals from tracts. 



Afferent and Efferent Suprasegmental Paths 



These paths are paths from receptors of body and head to cere- 

 bellum, midbrain roof (colliculi) and pallium and paths from cere- 

 bellum, midbrain roof and pallium to effectors of head and body. 

 There are also paths connecting pallium, mid-brain roof and 

 cerebellum. 



Afferent Suprasegmental Paths 



A. Afferent Pallial 



I. General Somatic Sensation: Spinal and trigeminal ganglionic -|- spino- 

 thalamic and bulbo-thalamic (medial fillet) crossed + thalamo-pallial (to post- 

 central cortex) neurones. (Fig. 330.) 



II. Splanchnic Sensation, including Taste. This important path is not well 

 known. The gustatory path enters by ganglionic neurones of nerves V (?), 

 IX and X (fasciculus solitarius). Its secondary tract may lie partly in the medial 

 fillet. 



III. Hearing (cochlear) : Spiral ganglionic -}- lateral fillet (crossed) and 

 brachium of inferior colliculus -|- geniculo-pallial (to temporal cortex) neurones 

 (Fig. 33S). 



IV. Vestibular: A somewhat doubtful path except perhaps to the pallium 

 through the cerebellum (paths X -|- VII). 



