SKELETAL MUSCLE 



127 



Muscle fiber. Connective tissue. 



been studied with conflicting results. Schultze finds that at the end of 

 the muscle fiber the myofibrils are no longer differentiated into light and 

 dark bands, but pass directly into the tendon fibrils, with which they are 

 continuous (Fig. 118). "Muscle fibrils and tendon fibrils are parts of a 

 single structure." (Arch. f. mikr. Anat., 1912, vol. 79, pp. 307-331). But 

 Baldwin finds that the ends of the muscle fibers are primarily conical and 

 are covered with sarcolemma; and the tendon fibrils connect with the 

 sarcolemma at the apices of the cones. The processes of sarcolemma are 

 thus primarily "dovetailed" into the tendon. Secondarily the cones 

 may blend to form a thickened flat layer to which perichondrial or perios- 

 teal fibers are attached. In no case is the sarcolemma penetrated by 

 muscle fibrils or tendon fibrils, and therefore there is no continuity between 

 them (Morph. Jahr., 1912, vol. 45, pp. 249-266). Thus Baldwin defends 

 the generally accepted opinion. 



Muscles are abundantly supplied with vessels and nerves, which are 

 imbedded in the perimysium. The lymphatic vessels end in the septa 

 without extending among the individual muscle fibers; but the blood 

 vessels, through capillary 

 branches, continue further and 

 run between adjacent fibers, Connective tissue 

 thus forming a plexus with 

 elongated rectangular meshes. 

 The nerves are chiefly motor, 

 and a branch ends in contact 

 with every muscle fiber, to 

 which it transmits the impulse 

 for contraction. Muscles also 

 contain sensory nerves, having 

 "free endings" and probably 

 terminating also around the muscle spindles. The spindles are slender 

 bundles of poorly developed fibers, generally situated near the septa 

 formed by the internal perimysium, as seen in Figs. 116 and 119. All 

 the muscle spindles are formed during embryonic life, and their abun- 

 dance and distribution in the various muscles in embryos have been 

 studied by Gregor (Arch. f. Anat. u. Entw., 1904, pp. 112-194). They 

 have not been found in all muscles, and in certain muscles they are 

 regularly more numerous than in others. Thus they have been reported 

 as absent from the muscles of the eye, face, pharynx, small muscles of 

 the larynx, the Mm. ischiocavernosus and bulbocavernosus, and certain 

 others, including a- large part of the diaphragm. They are numerous in 

 the distal muscles of the limbs, and in certain muscles of the neck. The 

 finer structure of the nerve terminations, both motor and sensory, will be 

 considered with the nervous system. 



Cross section 

 of nerve. 



Muscle fibers Nucleus Nucleus of the 

 of the of the sarcolemma. ; 



spindle, perimysium. 



FIG. 119. THE MUSCLE SPINDLE SHOWN IN FIG. 116. 

 X 240. 



