442 THE ORGANS 



orate structures. These cells constitute the receptors and probably render the 

 various nerve terminations they envelop, more or less inaccessible to all but one 

 particular kind of stimulus. The receptors described above are scattered through- 

 out head and body {general or common senses) as distinguished from those which 

 are concentrated into the organs of the special senses (smell, sight, hearing, taste) 

 present only in the head (pp. 480, 481 and Chap. XXIII). The various stimuli 

 received by them may give rise to sensations of light pressure or touch (tactile 

 cells and tactile corpuscles, terminations in hair sheaths), temperature and pain 

 (dififuse terminations in epithelium and connective tissue?), muscle-tendon sense 

 of movement and position (muscle spindles and possibly end bulbs, etc., in 

 muscles, tendon organs of Golgi). These may be roughly grouped into general 

 cutaneous or superficial sensation and deep sensation (muscle-tendon and. other 

 bodily sensations). All receptors, both of general and special senses, may be 

 classified (Sherrington) as those receiving stimuli from the external world {extero- 

 ceptors, of superficial sensation, smell, sight, and hearing), those concerned 

 with visceral reactions {iutcro-ccptors, including taste) and those giving infor- 

 mation of bodily changes {proprio-ceptors, deep sensation). 



The central processes of the cerebro-spinal ganglion 

 CELLS enter the central nervous system as the fibres of the afferent 

 root, the entire bundle of afferent root fibres of a single nerve consist- 

 ing of all the central processes of the corresponding ganglion. Hav- 

 ing entered the central nervous system, the central processes divide 

 into ascending and descending arms, as already mentioned (p. 425). 

 In the spinal cord the ascending arms are longer than the descending 

 arms. In the brain the descending is usually the longer. These 

 arms give off collaterals. Both collaterals and also the terminals of 

 the arms enter the gray matter of the cord and segmental brain and 

 terminate around various cell bodies and dendrites (terminal 

 nuclei). 



THE SYMPATHETIC GANGLIA 



The sympathetic system of the neck and trunk consists of (i) a 

 series of vertebral or chain ganglia, lying ventro-lateral to the vertebrae, 

 connected with the cord by white rami comniunicantes and connected 

 with each other by longitudinal cords, (2) of gangliated prevertebral 

 plexuses connected with the vertebral ganglia and also connected 

 with ((3) ill-defined peripheral or terminal ganglia in the walls of the 

 viscera {e.g., plexuses of Auerbach and Meissner). The sympa- 

 thetic ganglia of the head are the ciliary, sphenopalatine, otic, and 

 submaxillary.. 



The peripheral processes of certain spinal ganglion cells pass via 



