544 



STRUCTURE AND ARRANGEMENT OF THE MUSCLES. 



The latter probably represent the natural source of nutrition for the muscle- 

 fibers. In amphibia, birds, fish, and insects, the muscle-corpuscles are situated in 

 the axis of the fiber between the fibrils. 



The protoplasm of the muscle-corpuscles is further connected with the proto- 

 plasm that throughout the entire muscle-fiber forms longitudinally and trans- 

 versely a network of fibers on the fibrils the sarco plasm. The transverse fibers 

 follow the course of Hensen's and the Krause-Amici lines; the longitudinal fibers 

 pass in the interstices between Cohnheim's fields. The amount of sarcoplasm is 

 greater in the lower than in the higher animals. 



The relation of the muscle-fibers to the tendons varies. According to Toldt, the 

 delicate connective-tissue elements that surround the individual muscle-fibers 

 pass over the extremity of the latter directly into the elements of the tendon. 

 Apart from this it may happen that the extremities of the muscle-fibers are at- 

 tached by a special cement-substance to the plane surface or in shallow depressions 

 at the extremity of the independently formed tendon (Fig. 184, 12 S). In arthro- 

 pods there is doubtless also a direct transition of the sarcolemma into the substance 

 of the tendon. 



The tendons consist of parallel bundles of fibrillar connective tissue, containing 

 connective-tissue corpuscles and elastic fibers. They are covered by a loose 

 sheath of connective tissue, the peritendinemn, which contains the blood-vessels, 

 the lymphatics, and the nerves. The tendons pass through sheaths, whose slip- 

 pery synovial fluid fa- 

 vors the gliding move- 

 ment. In some situa- 

 tions the extremities of 

 the muscle-fibers are at- 

 tached directly to the 

 fixed point ; in other sit- 

 uations, such as the face, 

 they terminate among 

 the tissue-elements of 

 the skin or the fasciae. 



Motor Nerves. The 

 trunk of the nerve, as a 

 rule, enters the muscle 

 at its geometrical center ; 

 hence, the point of en- 

 trance in long muscles 

 with parallel fibers or in 

 spindle-shaped muscles 

 is situated near the mid- 

 dle. If the muscle with 

 parallel fibers is more 



than 2 or 3 cm. wide, several branches enter side by side at its middle. In tri- 

 angular muscles the point of entrance of the nerve is displaced toward the tendin- 

 ous point of convergence of the muscle-fibers, the amount of displacement varying 

 with the degree of convergence and the consequent thickness of the pointed ex- 

 tremity of the muscle. In general, the entrance of the nerve-trunk into a muscle 

 may be suspected to take place at that point where the least displacement of mus- 

 cular tissue occurs during the contraction of the muscle. 



The motor nerve destined for a certain muscle does not originally contain as 

 many fibers as there are muscle-fibers; in the eye-muscles of man about seven 

 muscle-fibers correspond to three nerve-fibers in the trunk; in other muscles, in 

 the dog, there is one nerve-fiber to from forty to eighty-three muscle-fibers. Hence, 

 it is necessary, in the course of their ramification in the muscle, for the separate 

 nerve-fibers to subdivide dichotomously. 



In warm-blooded animals each muscle -spindle has only one point of innerva- 

 tion, while the longer spindles of cold-blooded animals have several. The 

 medullated fiber enters the muscle-fiber and forms at its point of entrance a 

 nodular prominence, the nerve end-bulb (Fig. 184, i, e). In this transition the 

 neurilemma fuses directly with the sarcolemma, the medullary substance disap- 

 pears, and the axis-cylinder becomes transformed into a flattened ramification, 

 the nerve end-plate, or nerve-arborization, which rests upon a finely granular 

 accumulation of sarcoplasm (Fig. 185), in which nuclei are present. Accord- 

 ing to Kiihne the connection of the nerve with the muscle-fiber is established 

 only through the coalescence of the end-plate with the substratum of sarco- 



Nerve. 



Muscle 

 nucleus. 



FIG. 185. Muscle-fibers with Nerve-ending, from the lizard 

 (after W. Kiihne). 



