THE NEURO-MUSCULAR SPINDLE 



133 



Fig. 6 Neiiro-muscular spindle from a 55 mm. pig embryo, showing both 

 muscle fibers and a myoblast included in the same ending. (Obj., Leitz, 1/12 oil 

 immersion; ocular 4.) 



Fig. 7 A sensory ending composed ot only two muscle fibers from a 65 mm. 

 pig embryo. The br;.nch to the spindle is seen leaving the nerve. The neuro- 

 fibrils end both as free bulbous tips on the muscle fibers and with delicate branch- 

 ing upon the gray placques, which have nothing to do with muscle nuclei. (Obj. 

 Leitz, 1/12 oil immersion; ocular 4.) 



for the muscle development it must be the sensory ending, for 

 several anomalies which have been described (Leonowa '93; 

 Frazier '95) show a fetus dehvered at term in which the spinal 

 cord with the ventral roots of the spinal nerves are absent while 

 the muscles are normally developed with their sensory endings 

 and peripheral nerves up to and inchiding the posterior root gan- 

 glia. I know of no such cases, however, where the muscles were 

 present and the peripheral sensory system lacking — unless some 

 cases of amyotonia congenita fall into this class. But even in 



