6o 



NORMAL HISTOLOGY. 



possess a relatively large amount of sarcoplasm, with nuclei embedded 

 not only beneath the sarcolemma, but also in deeper parts of the fibres 

 (Fig. 76). Although not present in mammals generally in sufficient numbers 

 to affect the appearance of entire muscles, the ' ' red ' ' fibres occur probably 

 in all striated muscular tissue upon which devolves prolonged and frequently 

 repeated effort. Such fibres, therefore, are present in the heart, eye-muscles, 

 and the muscles of respiration and of mastication. Possessing, as they do, 



a larger proportion of undifferentiated 

 cytoplasm, the sarcoplasm, the red 

 fibres are better able to withstand 

 the fatigue of contraction. The pale 



FIG. 76. Portion of the soleus muscle of the rabbit 

 in transverse section. The more coarsely stippled 

 fibres are of " red " muscle; they also contain nuclei 

 within the sarcous substance. X 160. 



Longitudinal 



Transverse 



FIG. 77. Injected voluntary muscle, showing 

 arrangement of interfascicular vessels and cap- 

 illaries. X 50. 



fibres, on the contrary, gain in rapidity of contraction at the expense of 

 early exhaustion. 



The blood-vessels supplying striated muscle are very numerous. 

 The larger arteries and accompanying veins enter the muscle along the 

 connective tissue septa and divide into smaller branches which run between 

 the fasciculi. These vessels give off twigs which pass between the finer 

 bundles of fibres and ultimately break up into dense capillary networks that 

 surround the individual fibres with long rectangular meshes. The relation of 

 the blood-vessels to cardiac muscle is exceptionally intimate, the capillaries 

 not only enclosing the trabeculae with rich networks, but also lying in grooves, 

 or even in channels, surrounded by the muscular tissue. The lymphatics 

 are represented by the clefts within the connective tissue around the fibres 

 and by definite lymph-vessels which accompany the blood-vessels in the 

 larger tracts of connective tissue. The nerves supplying striated muscle 

 include both motor and sensory fibres. The former terminate in specialized 

 end-arborizations, the motor nerve-endings, which lie beneath the sarcolemma 

 and upon the sarcous substance. The sensory fibres are connected with the 

 neuro-muscular end-organs, or muscle-spindles. The description of both vari- 

 eties of terminations will be found under the Nerve-Endings (pages 84, 85). 



