462 



HUMAN ANATOMY. 



deeper parts of the fibre (Fig. 480). The longitudinal striation is also unusually con- 

 spicuous, due to the exceptional amount of interfibrillar sarcoplasm. Although not 

 present in mammals generally in sufftcient quantity to affect the appearance of entire 

 muscles, the peculiar ' ' red' ' fibres are found in many localities intermingled with the 

 more usual pale variety. Klein has described such fibres in the diaphragm, and. 

 according to the investigations of Griitzner and of J. Schaffer, it is probable that they 

 are found in all muscular tissue upon which devolves prolonged effort. These fibres 

 are, therefore, present in the heart, the eye muscles, and the muscles of respiration and 

 of mastication. The red fibres must be regarded as representing a less complete 

 differentiation of the muscle-cell and as possessing consequently a larger proportion 

 of reserve protoplasm ; they are better able to withstand the fatigue of contractions 

 than those in which the specialization of a larger part of the cytoplasm has occurred. 

 The pale fibres gain in rapidity of contraction at the expense of early exhaustion. 



Attachment of the muscular fibres, whether to other fibres or to tendons, is 

 accomplished by the union of the sarcolemma with the connective or tendinous tissue 



Fig. 480. 



fee \ 







Portion of the soleus muscle of the rabbit in trans- 

 verse section. The more coarsely stippled fibres are of 

 "red" muscle; they also contain nuclei within the sar- 

 cous substance. X i6o. 



Fig. 481. 



i^ 





s] 





^'iTi-fl 



h 



1^"- 







Section of tendon, showing termination of muscle- 

 fibres. X 200. 



and never by direct fusion of the connective tissue with the sarcous substance, the 

 latter remaining completely invested b)^ its sheath. On joining a muscle (Fig. 481), 

 the tendon-tissue subdivides into small bundles which receive and surround the pointed 

 ends of the muscle-fibres, the fibrous tissue becoming attached to the sarcolemma, 

 while the areolar tissue between the tendon-bundles blends with that separating the 

 muscle-fibres. , 



Cardiac Muscle. — The striped muscle of the heart, in addition to the pecu- 

 liarity of being beyond the control of the will, although striated, presents certain 

 modifications in the form and arrangement of its fibres which call for special con- 

 sideratio.n. According to the views formerly held, the histological unit of the myo- 

 cardium was the branched fibre-cell (Fig. 482), by the apposition of which the sheets 

 of muscular tissue were formed. The fibre-cell was regarded as a short branched 

 fibre, devoid of a sarcolemma and possessing a nucleus surrounded by a considerable 

 area of undifTerential sarcoplasm. Studies of the histogenesis of cardiac muscle show 

 that the contractile tissue arises as a continuous network, or syncytium, without cell 

 boundaries, but provided with nuclei. The subsequent appearance of the transverse 



