416 THE TISSUES. 



It is also certain that divisions of the nerve-fibres occur in the 

 muscles of man, though they are rare and detected with difficulty. 

 (Fig. 269.) Their relation to the loops is still to be made out. 



In many of the small muscles the extent of space to which the 

 nerve-fibres are distributed is very limited. In a portion of the 

 superior belly of the omo-hyoid, three inches long, the portion to 

 which the nerves are distributed is not more than five to six lines 

 in length. The trunk of the nerve enters in the middle of the 

 transverse axis of the muscle, and divides into two primary branches, 

 one passing to the right and the other to the left border of the mus- 

 cle. Each of these gives off numerous anastomosing branches of 

 all sizes, thus supplying the entire thickness of the muscle from 

 the most superficial to the deepest layers. The rest of the muscle 

 usually presents a complete deficiency of nerves. The same con- 

 ditions obtain in the lower belly of the omo-hyoid, in the sterno- 

 hyoid, sterno-thyroid, subcruralis, &c. It appears to be true in 

 respect to the larger muscles also, that their separate portions are 

 in connection with the nervous plexus, only at a point of limited 

 extent. Whether the muscular fibres are in contact with nerves 

 only at a single point when the former are of the greatest length 

 (as in the sartorius, latissimus dorsi, &c.), is not yet decided. 



Nerves are also found accompanying the vessels of muscles 

 (nervi vasorum); but these present no peculiarities. They are com- 

 posed of the finest fibres alone, and are distributed to the arteries 

 and veins (seldom to the smallest), but not to the capillaries. How 

 they terminate is still unknown. Some fibres also from the muscu- 

 lar plexus before described, occasionally join those of the vessels. 



The larger tendons contain the vascular nerves only, and the 

 smaller none at all. The fasciae and the sheaths of the tendons, as 

 well as the synovial capsules (bursaa mucosae), contain none. 



Peculiarities in the Lower Animals. In the invertebrata, the nerve- 

 fibres are known to terminate in the muscles by free extremities, 

 which, after expanding, are inserted into the muscular fibres. The 

 divisions are sometimes trifid. In them, also, every muscular fibre 

 appears to have a nerve-fibre distributed to it; and often accompa- 

 nying it for a considerable distance, and forming loops or spirals 

 around it. In the amphibia the divisions are multiple (Fig. 270), 

 and even eight-fold. ( Wagner.} The ultimate filaments are pale 

 and have a simple contour line. They do not penetrate the mus- 

 cular fibre, but are merely closely applied to it, either obliquely, 

 transversely, or longitudinally, for some distance; becoming in all 



