MOTOR ENDINGS. 



107 



substance, sometimes described as an inner bulb, and this is enclosed in 

 a few concentric layers of cells which are continuous with the sheath of 

 the nerve. Cylindrical corpuscles are found in the mucous membrane 

 of the mouth and in the connective tissue of muscles and tendons. 



Lamellar corpuscles [Pacinian corpuscles] are macroscopic elliptical 

 structures, 2-4.5 mm - l n an d I ~ 2 mm - wide (Fig. 130). They may 

 have as many as fifty concentric layers of flattened capsule cells between 

 which there are spaces containing fluid. A single large nerve fiber enters 

 one end of the corpuscle and loses its myelin as it traverses the lamellae. 

 It extends through the semifluid inner bulb without obvious branches, 

 sometimes being flattened and band-like; it may fork at its further end or 

 form a coil of branches. Special methods have shown that the axial 

 fiber may possess many short lateral 

 branches ending in knobs, and that 

 one or more delicate fibers may enter 

 (or leave) the corpuscles in addition to 

 the large one just described; they form 

 a net surrounding the axial fiber. A 

 small artery may pass into the corpus- 

 cle beside the nerve and supply the 

 lamellae with capillaries. Lamellar 

 corpuscles are abundant in the subcu- 

 taneous tissue of the hand and foot and 

 occur in other parts of the skin, in the 

 nipple, and in the territory of the pu- 

 dendal nerve; they are found near the 

 joints (particularly on the flexor side) 

 and in the periosteum and perimysium, 

 the connective tissue around large blood 

 vessels and nerves, and in the tendon sheaths; also in the serous mem- 

 branes, particularly in the mesenteries. As they are usually cut obliquely 

 or transversely the student should expect to find the lamellae completely 

 encircling the inner bulb. 



MOTOR ENDINGS. The motor nerve endings are the terminations of 

 efferent nerves in contact with smooth, cardiac or striated muscle fibers. 

 The nerves to the smooth muscles are a part of the sympat etic system. 

 They are non-medullated fibers which branch repeatedly, forming plexuses. 

 From the plexuses very slender varicose fibers proceed to the muscle 

 cells, in contact with the surface of which they end in one or two terminal 

 or lateral nodular thickenings. Probably each muscle cell receives a nerve 

 termination. Except that the nerve endings in heart muscle are a little 



Axis cylinder. 



Inner bulb. 



Capsules. 



Nerve fiber. 

 Artery. 



Fat cells. 



FIG. 130. SMALL LAMELLAR CORPUSCLE FROM 

 THE MESENTERY OP A CAT. X so. 



The cells lining the capsules can be recognized 

 by their shaded nuclei. The myelin of 

 the nerve fiber may be traced to the 

 inner bulb. 



