172 



PEEIPHEKAL NERVE TERMINATIONS: END ORGANS 



At the surface of the muscle cell the nerve fiber loses its medullary 

 sheath, its neurolemma becomes continuous with the sarcolemma of the 

 muscle cell, and its naked axis cylinder divides into two to five branches, 

 which end, often after repeated subdivision, in flattened terminal disks, 

 distributed in mammals over a limited, in amphibians over a broad area, 

 but which never completely encircle the cylindrical muscle cell. 



The terminal expansions of the axon rest upon a granular, slightly 



raised sole plate which contains many 

 ovoid muscle nuclei, the sole nuclei. 



2. Muscle Spindles (N euro mus- 

 cular Spindles, N euromuscular End 

 Organs). These are sensory nerve 

 endings which are concerned with 

 the so-called muscle sense. They are 

 especially numerous in the extrinsic 

 muscles of the tongue, in the small 

 muscles of the hand and foot, and in 

 the intercostal muscles ( Huber , Amer. 

 Jour, of Anat., 1902). They have 

 not been found in the muscles of the 

 diaphragm. A detailed description of 

 the developing ueuromuscular spin- 

 dle in the extrinsic eye muscles of the 

 pig has recently been given by Sutton 

 (Am. Jour. Anat., 18, 1, 1915). He 

 describes a coarsely granular 'plaque,' 

 different from both muscle and nerve, 



FIG. 191. A MUSCLE SPINDLE FROM 

 THE PSOAS MAGNUS OF MAN. 



1, intrafusal muscle fibers; 2, nerve 

 fibers; 3, axial sheath; 4, connective 

 tissue capsule; 5, muscle fibers of an 

 adjacent fasciculus; 6, peri-axial 

 lymphatic spaces; 7, blood-vessel. 

 Hematein and eosin. X 470. 



which he inclines to regard as an 



'intermediary structure,' perhaps a receptor substance analogous to the 

 sole plate of motor endings. 



A muscle spindle contains from five to twenty striated muscle fibers 

 of small size, and an almost equal number of nerve fibers. The whole 

 is inclosed within a connective tissue capsule of considerable thickness. 

 The bundle of intrafusal muscle fibers is again surrounded by a delicate 

 a. rid I shcalh of connective tissue which is united to the capsule by bands 

 of fine fibrous tissue which span the broad peria.rinl lymphatic space. 

 The larger of these fibrous bands support the nerve fibers, on their way 

 to the intrafusal muscle cells, together with several small blood-vessels. 



The muscle spindles form long fusiform bodies (from 1 to 5 milli- 

 meters in length) whose muscle fibers at the pole of the spindle may be 



