NERVE-TERMINATIONS. 



1019 



FIG. 875. 



Corpuscles of Herbst from bill of duck ; a, longitudinal, b, transverse 

 section ; n, nerve traversing lamellae of capsule ; axis-cylinder within core 

 is surrounded by cells. X 360. 



is occupied by a core or inner bulb of semifluid substance in which the naked 

 axis-cylinder is embedded. 



On joining the proximal pole of the corpuscle, the fibrous (Henle's) sheath of 

 the nerve-fibre blends with the outer lamellae of the capsule, while the medullary 

 coat is retained during the somewhat tortuous path of the fibre through the capsule 

 as far as the core. Here the remaining envelope of the nerve-fibre disappears, the 

 terminal part of its course, 

 through the core, being as 

 the naked axis-cylinder. At 

 a variable distance but often 

 just before gaining the distal 

 pole of the core, the axis- 

 cylinder divides into from 

 two to four branches, each of 

 which terminates in a slightly 

 expanded end-knot. Some- 

 times shortly after penetrat- 

 ing the capsule, the nerve- 

 fibre splits into two or more 

 axis-cylinders which then 

 share the common envelope 

 of semifluid axial substance. 



Similar end-organs, the 

 corpuscles of Herbst, 

 occur in the velvety skin 

 covering the bill and in the 

 tongue of water-fowl. They 

 closely resemble the Pacinian 

 bodies of mammals, but differ 

 in being generally smaller, relatively broader, and in exhibiting a row of cubical cells 

 within the core and around the axis-cylinder. These cells are regarded as corres- 

 ponding to the large cells enclosing the tactile discs in the Grandry's corpuscles. 



The Golgi-Mazzoni corpuscles, found in the subcutaneous tissue of the pulp 

 of the fingers, are modifications of the ordinary Pacinian end-organs. They differ 

 from the latter in possessing fewer lamellae, a relatively larger core and a more 

 branched axis-cylinder. 



Neuromuscular Endings. First described by Kolliker and by Kiihne, 

 although previously seen by Weissmann, these end-organs, often termed muscle- 

 spindles, are now regarded as sensory endings that are probably concerned in afford- 

 ing impressions as to tension or "muscle-sense". They lie within the connective 

 tissue separating the bundles of voluntary muscle-fibres and are long spindle-shaped 

 structures, varying in length from 1-5 mm. or more and in width from .I-.T, mm. 

 where broadest. They are widely distributed, being probably present in all the 

 skeletal muscles, and are especially numerous in the small muscles of the hand and 

 foot. They are uncertainly found, however, in the intrinsic muscles of the tongue and 

 in the eye muscles, although within the tendons of the latter very similar (neuro- 

 tendinous} end-organs have been demonstrated. 



Each spindle consists of a capsule, composed of a half-dozen concentric layers 

 of fibrous tissue, which encloses a group of usually from three to ten, but sometimes 

 as many as twenty, striped muscle-fibres, medullated nerves, blood-vessels and inter- 

 spersed connective tissue. These intrafusal fibres, as. they are called, differ from 

 those of the surrounding muscle in being much smaller in diameter and length, 

 markedly tapering towards either end, more coarsely but less distinctly striated, and 

 in possessing nuclei within the sarcous substance. The striations are not equally 

 distinct in all parts of the fibres, being much less evident in the middle zone than 

 towards the ends. The fibres are more numerous and of greater diameter in the 

 equatorial region than near the poles of the spindle. 



The intrafusal fibres collectively are surrounded by a thin special connective 

 tissue envelope, the axial sheath, between which and the capsule lies the periaxial 



