458 



XERVES OF A MUSCLE. 



supplied only by one artery and one vein, thus being unlike the kidney, spleen, &c. Each 

 muscle usually receives several branches from different arteries, and branches enter it at certain 

 distances along its whole length. The artery and vein usually lie together in the connective- 

 tissue of the perimysium, while the capillaries lie in the endomysium. The capillaries lie 

 between the muscular fibres, but outside the ssrcolemma, where they form an elongated rich 

 plexus with numerous transverse branches (fig. 308). The lymph to nourish the sarcous sub- 

 stance must traverse the sarcolemma to reach the former. In the red muscles of the rabbit 

 {e.g., semitendinosus) the capillaries are more wavy, while on the transverse branches of some 

 of the capillaries, and on the veins, there are small, oval, saccular dilatations, which act as 

 reservoirs for blood (Ranvicr). ] 



[Lymphatics. We know very little of the lymphatics of muscle, although the lymphatics of 

 tendon and fascia have been carefully studied by Ludwig and Schweigger-Seidel. There are 

 lymphatics in the endomysium of the heart, which are continuous with those under the peri- 

 cardium. This subject still requires further investigation. Compare the lymphatics of the 

 fascia lata of the dog (fig. 227, 201.] 



Entrance of the Nerve. The trunk of the motor nerve, as a rule, enters the muscle at its 

 geometrical centre (Schicalbe) ; hence, the point of entrance in muscles with long, parallel, or 

 spindle-shaped fibres lies near its middle. If the muscle with parallel fibres is more than 2 to 

 8 centimetres [1-3 inches] in length, several branches enter its middle. In triangular muscles, 

 the point of entrance of the nerve is displaced more towards the strong tendinous point of con- 

 vergence of the muscular fibres. A nerve- fibre usually enters a muscle at the point where there 

 is the least displacement of the muscular substance during contraction. 



Motor Nerve. Every muscle-fibre receives a motor nerve-fibre (fig. 302, 1, N). 

 Each nerve does not contain originally as many motor nerve-fibres as there are 



muscular fibres in the muscle 

 it enters; in the human eye- 

 muscles, there are only 3 

 nerve-fibres to 7 muscular 

 fibres ; in other muscles 

 (dog), 1 nerve-fibre to 40 or 

 80 (Tergast). Hence, when 

 a nerve enters a muscle it 

 must divide, which occurs 

 dichotomously [at . Ranvier's 

 nodes], the structure under- 

 going no change until there 

 are exactly as many nerve- 

 fibres as muscular fibres. In 

 warm-blooded animals each 

 muscular fibre has only one, 

 while cold-blooded animals 

 have several points of insertion of the nerve-fibre (Sandmann). A nerve-fibre enters 

 each muscular fibre, and where it enters it forms an eminence {Doyere, 1840), the 

 "motorial end-plate" (figs. 302, 1, e, 309, 310, 311). 



[The elaborate investigations of K. Mays on the exact distribution of nerve-fibres 

 in the muscles of the frog have conclusively proved apart from experimental reasons 

 that parts of muscles receive no nerve-fibres at all, large portions being free from 

 nerves. This has been proved for all classes of vertebrates except osseous fishes.] 



[The mode of termination of a motor nerve in a muscular fibre is not the same in all animals, 

 but in every case it pierces the sarcolemma, and its ultimate distribution has a distinct hypo- 

 lemmal character. The Doyere's eminence is present in most mammals and reptiles, but in 

 amphibians and birds, the ending is flat on the muscle-fibre. Most of the results known to us 

 have been worked out by Kiihne. The nerve-endings, then, are confined to very small spots 

 or areas on the muscular fibres, termed by Kiihne " fields of innervation." Most nerve-fibres 

 have only one such field, but very long fibres may have, at most, eight. Ono or more medul- 

 lated nerve-fibres pass as preterminal or epilemmal fibres from the point of division of the 

 nerve-fibre to the muscular fibre, to pass into the nerve-endings. The nerve-endings consist 

 of divisions of the axial cylinder, which are distributed over the sarcous substance without 

 (so far as is known) forming any direct connection with it. The endings, however, lie in direct 



Nerve. 



Fig. 309. 

 Muscular fibres with motorial end-plates. 



