86 HUMAN PHYSIOLOGY. 



nerve; for if the nerve be separated from the ganglion, it undergoes degene- 

 ration in the course of a few days, in the direction in which it carries 

 impressions, i. e., from the periphery to the centres; if the nerve be divided 

 between the ganglion and the cord, the central end only undergoes degene- 

 ration. The nutrition of the anterior root is governed by nerve cells in the 

 gray matter of the cord ; for if these cells undergo atrophy, or if the nerve 

 be divided, it undergoes degeneration outward. 



Nerve Terminations. (l) Central. Both motor and sensory nerve 

 fibres, as they enter the spinal cord and brain, lose their external invest- 

 ments, and retaining only the axis cylinder, ultimately become connected 

 with the processes of the gray cells. 



(2) Peripheral. As the nerves approach the tissues to which they are 

 to be distributed, they inosculate freely, forming a plexus from which the 

 ultimate fibres proceed to individual tissues. 



Motor Nerves. In the voluntary or striped muscles the motor nerves 

 are connected with the contractile substance by means of the " motorial 

 end plates ; " when the nerve enters the muscular fibre the tubular mem- 

 brane blends with the sarcolemma, the medullary layer disappears, and the 

 axis cylinder spreads out into the form of a little plate, granular in character, 

 and containing oval nuclei. 



In the unstriped or involuntary muscles, the terminal nerve fibres form 

 a plexus on the muscular fibre cells, and become connected with the 

 granular contents of the nuclei. 



In the glands nerve fibres have been traced to the glandular cells, where 

 they form a branching plexus from which fibres pass into their interior and 

 become connected with their substance, and thus influence secretion. 



Sensitive Nerves terminate in the skin and mucous membranes, in 

 three distinct modes, e. g. t as tactile corpuscles, Pacinian corpuscles, and as 

 end bulbs. 



The tactile corpuscles are found in the papillae of the true skin, especially 

 on the palmar surface of the hands and fingers, feet and toes ; they are 

 oblong bodies, measuring about -$fa of an inch in length, consisting of a 

 central bulb of homogeneous connective tissue surrounded by elastic fibres 

 and elongated nuclei. The nerve fibre approaches the base of the corpuscle, 

 makes two or three spiral turns around it, and terminates in loops. They 

 are connected with the sense of touch. 



The Pacinian corpuscles are found chiefly in the subcutaneous cellular 

 tissue, on the nerves of the hands and feet, the intercostal nerves, the 

 cutaneous nerves, and in many other situations. They are oval in shape, 



