376 MYOLOGY 



plasmic material (the clear substance of the sarcomere) recedes into the sarcous 

 element, causing the sarcomere to widen out and shorten. The contraction of the 

 muscle is merely the sum total of this widening out and shortening of these bodies. 

 Vessels and Nerves of Striped Muscle. The capillaries of striped muscle are 

 very abundant, and form a sort of rectangular network, the branches of which run 

 longitudinally in the endomysium between the muscular fibers, and are joined at 

 short intervals by transverse anastomosing branches. In the red muscles of the 

 rabbit dilatations occur on the transverse branches of the capillary network. The 

 larger vascular channels, arteries and veins, are found only in the perimysium, 

 between the muscular fasciculi. Nerves are profusely distributed to striped muscle. 

 Their mode of termination is described on page 730. The existence of lymphatic 

 vessels in striped muscle has not been ascertained, though they have been found in 

 tendons and in the sheaths of the muscles. 



Ossification of muscular tissue as a result of repeated strain or injury is not infrequent. It 

 is oftenest found about the tendon of the Adductor longus and Vastus medialis in horsemen, 

 or in the Pectoralis major and Deltoideus of soldiers. It may take the form of exostoses firmly 

 fixed to the bone e. g., "rider's bone" on the femur or of layers or spicules of bone lying in 

 the muscles or their fasciae and tendons. Busse states that these bony deposits are preceded 

 by a hemorrhagic myositis due to injury, the effused blood organizing and being finally converted 

 into bone. In the rarer disease, progressive myositis ossificans, there is an unexplained tendency 

 for practically any of the voluntary muscles to become converted into solid and brittle bony 

 masses which are completely rigid. 



TENDONS, APONEUROSES, AND FASCLffl. 



Tendons are white, glistening, fibrous cords, varying in length and thickness, 

 sometimes round, sometimes flattened, and devoid of elasticity. They consist 

 almost entirely of white fibrous tissue, the fibrils of which have an undulating 

 course parallel with each other and are firmly united together. When boiled in 

 water tendon is almost completely converted into gelatin, the white fibers being 

 composed of the albuminoid collagen, which is often regarded as the anhydride of 

 gelatin. They are very sparingly supplied with bloodvessels, the smaller tendons 

 presenting in their interior no trace of them. Nerves supplying tendons have special 

 modifications of their terminal fibers, named organs of Golgi. 



Aponeuroses are flattened or ribbon-shaped tendons, of a pearly white color, 

 iridescent, glistening, and similar in structure to the tendons. They are only 

 sparingly supplied with bloodvessels. 



The tendons and aponeuroses are connected, on the one hand, w y ith the muscles, 

 and, on the other hand, with the movable structures, as the bones, cartilages liga- 

 ments, and fibrous membranes (for instance, the sclera) . Where the muscular fibers 

 are in a direct line with those of the tendon or aponeurosis, the two are directly 

 continuous. But where the muscular fibers join the tendon or aponeurosis at an 

 oblique angle, they end, according to Kolliker, in rounded extremities which are 

 received into corresponding depressions on the surface of the latter, the connective 

 tissue between the muscular fibers being continuous with that of the tendon. The 

 latter mode of attachment occurs in all the penniform and bipenniform muscles, 

 and in those muscles the tendons of which commence in a membranous form, 

 as the Gastrocnemius and Soleus. 



The fasciae are fibroareolar or aponeurotic laminae, of variable thickness and 

 strength, found in all regions of the body, investing the softer and more delicate 

 organs. During the process of development many of the cells of the mesoderm 

 are differentiated into bones, muscles, vessels, etc. ; the cells of the mesoderm which 

 are not so utilized form an investment for these structures and are differentiated 

 into the true skin and the fascise of the body. They have been subdivided, from 

 the situations in which they occur, into superficial and deep. 



