THE MUSCULAR TISSUES. 



6l 



The connective tissue uniting the larger bundles of muscle-cells 

 supports the blood-vessels and nerves. The larger blood-vessels 

 break up into capillary net-works, which pass between the muscle- 

 cells. The nerves, derived principally from the sympathetic system, 

 likewise penetrate the intercellular spaces and terminate between the 

 cells in the manner more fully described in the chapter devoted to 

 nerve-endings. Lymphatics occur, as in parts of the digestive 

 tract, closely associated with the muscular tissue. 



STRIATED OR VOLUNTARY MUSCLE. 



Striated or voluntary muscle, in addition to the extensive system 

 attached to the skeleton, supplies the special muscles connected with 

 many organs, including the tongue, pharynx, middle ear, larynx, 

 upper half of the oesophagus, diaphragm, generative organs, etc. 

 This form of muscle is composed of long, irregularly cylindrical fibres, 

 each of which represents the high specialization resulting from the 

 development of the single original embryonal cell ; the fibre is, 

 therefore, the structural unit of the striated muscular tissue, and 

 corresponds to the spindle fibre-cell of the involuntary variety. The 

 fibre of striped muscle comprises (a) the sarcolemma, (6) the muscle- 

 nuclei, and (c) the muscle-substance. 



Each fibre is closely invested by a clear, homogeneous, elastic 

 sheath the sarcolemma which, ordinarily, so tightly adheres to 

 the enclosed muscle-substance that the two are 

 optically blended together; in favorable positions, FIG. 71. 



as where breaks in the sarcous substance occur, 

 or after the action of water, the sarcolemma is 

 separated from the muscle-substance, and is then 

 seen in profile as a delicate line spanning the 

 break in the continuity of the fibre. The sar- 

 colemma forms a closed sac completely envel- 

 oping the contractile substance of the fibre. 



Immediately beneath the sarcolemma, lying 

 within minute depressions on the surface of the 

 muscle-substance, are the muscle-nuclei. 

 These are oval or fusiform, usually placed 

 parallel to the long axis of the fibre, and sur- 

 rounded, especially at their ends, by a small 

 amount of granular protoplasm. These accumu- 

 lations represent the meagre remains of the 

 indifferent protoplasm which has not undergone 

 conversion into the highly specialized muscle-substance of the fibre. 

 In mammalian muscle the nuclei lie always upon the surface of the 

 sarcous substance of the fibre and immediately beneath the sarco- 



Voluntary-musclc fibres, 

 somewhat broken after 

 treatment with water, 

 showing the sarcolemma 

 (s) in several places. 



