CHAPTER VIII. MUSCLE AND NERVE. 



1. Muscular Contraction. We have, in the skeleton, 

 a complicated apparatus of parts hinged and movable upon 

 one another ; the agent moving these parts is the same agent 

 that we find in the walls of the heart propelling the blood 

 through the circulation, in the alimentary canal squeezing 

 the food along its course, and universally in the body 

 where motion occurs, except only in the case of the waving 

 cilia, and those cells which (like the white blood-corpuscles) 

 have the power of amoeboid motion. This agent is 

 muscle. The action of muscle is familiar to most people in 

 the typical case of the biceps in the arm of an athlete. This 

 is a mass of " flesh " tapering at both ends, where it is 

 attached by tendons to the scapula and radius respectively. 

 When the arm is bent (or flexed, as it is technically termed) 

 this muscle is plainly seen to swell up in the centre. This 

 change of shape in a muscle is called contraction a some- 

 what unfortunate term, since in physical science " con- 

 traction" means a diminution in total volume. It must 

 be clearly understood that muscular contraction involves 

 no change in volume, but only change of shape the muscle 

 becoming shorter and thicker. As it does so, it pulls the 

 points of its attachment towards one another (just as a 

 stretched piece of elastic might do as it shortened itself), 

 and so the arm is bent. It is by similar changes in shape 

 of the appropriate muscles that all motions of the rabbit's 

 body are effected with the two exceptions already men- 

 tioned. 



If we examine a muscle histologically we find it is a 

 tissue-complex. Tt_pnnqiista of a g^at rna.ny y^t-scle- fibres. 

 united together into a coherent mass by connective tissue 

 containing blood- capillaries. Connective tissue (called the 

 endomysium) surrounds each individual fibre, and as a 

 muscle has abundant need of food and oxygen we find a 

 network of capillaries set close around each fibre. The 



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