THE MUSCULAR SYSTEM. 



THE muscles constitute 45 per cent, of the body-weight and 

 are the active agents of locomotion. 



They consist of two kinds the NON-STRIPED and the 

 STRIPED. The latter, being usually under the control of the 

 will (the heart being a notable exception), have also received 

 the name of voluntary., and the former, not under the control 

 of the will, involuntary. 



Microscopically, their structure is as follows : 



Non-striped muscular tissue is made up of elongated, con- 

 tractile, nucleated cells. They consist of minute fibres in bun- 

 dles, inclosed in extremely delicate sheaths of elastic tissue. 



They are held together by an albuminous cement and col- 

 lected by connective tissue, into groups or masses, one-tenth to 

 one five-hundredth of an inch in length. 



Non-striped muscular tissue is highly vascular and is sup- 

 plied with nerves from the sympathetic. 



Striped muscular tissue is made up of cylindroid fibres of 

 from one and a half to two inches in length and one tivo- 

 hundredth to one six-hundredth of an inch in diameter. They 

 are held together in bundles by the endomysium, a delicate fibro- 

 connective tissue. These bundles are collected into groups by 

 the perimysium, a stronger connective-tissue band, forming the 

 fasciculi of the fully formed muscle. Striped muscular tissue is 

 also highly vascular. 



The parts of an individual fibre are first, the sarcolemma, 

 a very delicate, transparent, elastic sheath; second, the mem- 

 branes of Krause, which appear as dark lines stretching across 

 the fibre at regular intervals, forming the third, or the compart- 

 ments of Krause, which contain the muscular substance. The 

 latter contain the nucleated muscle-corpuscles. 



The striped muscular fibres of the heart differ somewhat 

 from the preceding, being branched, and dividing and subdivid- 

 ing to form an intricate net-work. 



The muscles are connected to cartilages, ligaments, bones, 

 and skin, either directly or by aponeuroses or tendons. 



Aponeuroses are dense, white, fibrous membranes, serving to 

 connect the muscles with the structures to be acted upon. 



Tendons are white, fibrous, glistening cords. They are com- 

 posed of white, fibrous tissue, arranged into, bands or bundles, 



(132) 



