448 



THE ORGANS 



more than one muscle fibre. In the perimysium the nerve fibres 

 undergo further branching, after which the fibres lose their medul- 

 lary sheaths and pass to the individual muscle fibres. Here each 

 fibre breaks up into several club-like terminals. These terminals 

 are imbedded in a nucleated protoplasmic mass on the outside of 

 the muscle fibre and probably composed of sarcoplasm. It is stated 

 that the neurilemma of the nerve fibre is continous with the sarco- 

 lemma and that a continuation of the sheath of Henle covers'the 



■^' 



Fig. 315. — Motor nerve-endings in abdominal muscles of a rat. 



X170. (Szymonowicz.) 



Gold preparation. 



whole structure which is known as the motor end plate. As a rule 

 each muscle fibre is supplied with a single end plate, though in large 

 fibres there may be several. (Fig. 315.) 



THE SPINAL CORD 



The spinal cord encased in its membranes lies loosely in the ver- 

 tebral canal, extending from the upper border of the first cervical 

 vertebra to the middle or lower border of the first lumbar vertebra. 

 It is cylindrical in shape and continuous above with the medulla 

 oblongata, while below it terminates in a slender cord, the filum ter- 

 minale. At two levels, one in its cervical and one in its lumbar 

 region, the diameter of the cord is considerably increased, These are 

 known, respectively, as the cervical and lumbar enlargements. The 

 spinal nerve roots leave the cord at regular intervals, thus indicating 



