36 THE HUMAN BODY. 



the feathers of a pen (extensor muscles of fingers). Lastly, 

 certain organs, the heart for example, are nothing but 

 muscle, or rather an assemblage of muscles intimately 

 united. 



The muscles determine the form and volume of the body, 

 and especially of the limbs. The outline depends upon their 

 projection, and changes incessantly as they are in action or 

 in repose. They are disposed in layers, deep or superficial, 

 and united in groups or separated by sheaths and mem- 

 branous partitions. Their colour varies from deep red to 

 pale rose, 'according to the region of the body they occupy, 

 age, sex, the constitution and richness of the blood. The 

 stronger the muscle the redder it is, and it becomes still 

 brighter under the influence of exercise. 



The muscles of the human body number about 350, and 

 they are distinguished by names suggested by their form, 

 their locality, their functions, or their attachments. Some 

 are fixed to the skin, as several of the muscles of the face ; 

 others to muscles in their vicinity, as in the face and tongue; 

 others still to the cartilages, but the largest number to the 

 bones by means of the tendons or the aponeuroses, of which 

 we proceed to speak. 



Tendons, aponeuroses. In most of the muscles we can dis- 

 tinguish a fleshy portion, which is essentially the muscle, and 

 a fibrous portion, which is called either tendon or aponeurosis 

 according to its form. The tendons are fibrous cords of 

 variable length, rounded or flattened, of a pearl-white colour, 

 attached to the bones by one of their extremities and united 

 to muscular fibres by the other. The aponeuroses are 

 nothing but large thin tendons, a kind of fibrous web or band 

 which accompanies the muscles, separating them by partitions 

 or enveloping and uniting them in bundles. The tendinous 

 fibres are generally developed in the substance of the fleshy 

 part of the muscle, or on the surface, which they cover to a 

 certain extent. In the first instance they are inclosed, as it 

 were, by the muscle; in the second, they envelop it like a 

 sheath. This reciprocity gives great solidity to the whole. 



The muscles and tendons are united together by the direct 

 adherence of the extremities of their fibres, which takes place 



