NERVE-FIBERS. 65 



branches goes to a muscular fiber. Its primitive sheath is con- 

 tinuous with the sarcolemma, and the medullary sheath terminates. 

 The axis-cylinder breaks up into fine ramifications, which are em- 

 bedded in granular nucleated protoplasm ; this is a motor end-organ 

 or end-plate (Figs. 62-65). 



In involuntary muscle the nerve-fibers end in plexuses, from 

 which fine branches pass to the contractile fiber-cells. 



Nerve-fibers also end in special organs, of which there are 

 various kinds : End-bulbs of Krause, tactile corpuscles, Pacinian 

 corpuscles, organs of Golgi, and muscle-spindles. 



End-bulbs (Fig. 67). An end-bulb consists of a cylindrical, 

 oblong, or spheroidal body formed from the connective- tissue 

 sheath of a medullated nerve-fiber. Within this is a core with 

 many nucleated cells, in which the axis-cylinder terminates. End- 



Connective - 



tissue. 



Fibrils of axial - v SlH^^lffiaBStt^l^aH?^- ' Fibrils, 

 cord. 



Medullary 

 sheath. 



FIG. 61 .Transverse section through the sciatic nerve of a frog ; X 820 ; at a and ft 

 is a diagonal fissure between two Lantermann segments ; as a result, the medullary 

 sheath here appears double (Bohm and Davidoff). (Compare Fig. 60.) 



bulbs are found in the conjunctiva, in the papillae of the lips and 

 tongue, the skin and mucous membrane of the penis, the clitoris, 

 vagina, epineurium of nerve-trunks, and in tendon. 



In the synovial membrane of some joints, as in the fingers, 

 end-bulbs also occur, and are here called articular end-bulbs. 



Tactile Corpuscles. These consist of connective tissue which 

 forms a capsule, from which are given off membranous partitions 

 or septa. After winding around the corpuscle the axis-cylinder 

 enters it, and terminates in an enlargement. Tactile corpuscles 

 occur in the papillae of the skin of the hand, foot, front of the 

 forearm, lips, and nipple ; also in the mucous membrane of the 

 tip of the tongue and the conjunctiva lining the eyelids. 



Pacinian Corpuscles (Fig. 70). These are also called corpuscles 

 of Vater. Each corpuscle consists of concentrically arranged 

 layers of connective tissue, with nucleated cells. A medullary 



