MOTOR NERVE-ENDINGS. 85 



muscle-fibres. After repeated division during their course through the 

 capsule and periaxial space, the nerve-fibres pierce the axial sheath, lose 

 their medullary coat and terminate either as one or more ribbon-like branches 

 that encircle the muscle-fibres in annular or spiral windings, or, after further 

 subdivision, as branched telodendria in which the fibrils end in irregular 

 spherical or pyriform swellings. 



Neurotendinous Endings. In their general architecture, these 

 end-organs resemble the muscle-spindles. They lie within the interfascic- 

 ular connective tissue, at the junction of the muscle and tendon, and are 

 probably present in all tendons, although in variable numbers. Like the 

 neuromuscular endings, the tendon- spindles, as they are often called, are 

 long fusiform structures, from I.-I-5 mm. in length, surrounded by a 

 fibrous capsule. The latter encloses a group of from eight to twenty intra- 

 fusal tendon fasciculi, which are smaller and apparently less mature than 

 those composing the surrounding tendon-tissue. The intrafusal fasciculi 

 are invested by a fibrous axial sheath, between which and the capsule lies 

 a periaxial lymph-space. On reaching the spindle, after repeated branching, 

 the medullated nerve-fibres penetrate the capsule, with which their fibrous 

 sheaths blend, and undergo further division. The medullary coat is lost 

 after they pierce the axial sheath, the naked axis-cylinders then breaking up 

 into smaller fibrils that extend along the intrafusal fasciculi. The terminal 

 ramifications, applied to the surface of the fasciculi, vary in details. Some 

 arise as short lateral branches that partly encircle the fasciculi and end in 

 irregular plate-like expansions, while others terminate between the smaller 

 fasciculi. The tendon-spindles are probably concerned in appreciating the 

 degree of tension exerted by the pull of muscular contraction. 



The terminal cylinders, or Ruffin? s endings, are elongated slightly 

 fusiform end-organs, which supplement the fine sensory nerve-endings in 

 connective tissue. They lie at the junction of the corium and the sub- 

 cutaneous layer of the fingers and toes. They resemble somewhat the 

 tendon-spindles, being provided with a fibrous sheath which surrounds the 

 elaborate end-arborizations of the entering nerve-fibre. The latter, some- 

 times single but often double, loses its fibrous sheath on penetrating the 

 capsule, with which the sheath blends, and enters the connective tissue as a 

 naked axis-cylinder. This subdivides into numerous branches, which are 

 beset with irregular varicosities and end in small club-shaped expansions. 



MOTOR NERVE-ENDINGS. 



The motor endings include (a) the terminations of the axones of neurones, 

 whose cell-bodies (nerve-cells) are situated within the motor nuclei of the spinal 

 cord and brain-stem, that pass to voluntary muscle ; () the terminations of 

 sympathetic neurones that end in involuntary muscle and (c~) in cardiac muscle. 



Endings in Voluntary Muscle. On approaching their peripheral 

 destination, the medullated efferent nerve-fibres branch repeatedly, each fibre 

 in this way coming into relation with a number of muscle-fibres. When the 

 medullated nerve-fibre reaches the muscle-fibre which it supplies, its medul- 

 lary coat abruptly ends and the neurilemma becomes fused with the sarco- 

 lemma, while the axis-cylinder passes beneath the sarcolemma to terminate 

 in an end-plate. The latter appears as an oval field, from 40-60 ft in its 

 longest diameter, which is applied to the surface of the muscle-substance. 

 In profile it often shows as a slight elevation. Embedded within a nucleated 

 sheet of granular protoplasm, the sole plate, lie the terminal arborizations of the 



