LOCOMOTIVE ORGANS. THE MUSCLES. 159 



are therefore, likewise, passive organs of locomotion. Even the loose 

 cellular tissue, which immediately invests the muscles, and facilitates 

 their constant changes of form and position, may be similarly regarded. 



The Muscles. 



The microscopic structure and the vital properties of the muscular 

 tissue, both in man and animals, have already been fully described 

 (pp. 48, 130) ; and also the general mode of construction of the mus- 

 cles (pp. 21, 49). The number of separate muscles on the two sides 

 of the body is, according to the ordinary mode of division, upwards of 

 500. The muscles vary in size, some weighing only grains, and others 

 pounds, as, for example, certain minute muscles in the tympanum of 

 the ear, and the vasti muscles of the thigh ; in length, they range 

 from two lines to two feet. The form of muscles also varies consider- 

 ably, according to their position and use ; and so likewise does the 

 arrangement of their fasciculi. Usually these latter are disposed 

 longitudinally, but sometimes they form circular bands. On the 

 trunk of the body the muscles are generally broad and flat ; in the 

 limbs, on the other hand, they are narrow and elongated the deep 

 ones, however, being here also broad. Some of the broad muscles are 

 square ; others triangular, or lozenge-shaped ; and some are indented, 

 or serrated, at their edges ; the long muscles are flat and ribbon- 

 shaped, round and fusiform, or, when their fibres are attached ob- 

 liquely to the sides of a tendon, either penniform or semi-penniforrn. 

 For the most part, the muscles are attached by both their extremities 

 to the bones, either directly, or indirectly by means of the white, 

 flexible, but inelastic cords, called tendons ; but sometimes they are 

 attached to bone by one extremity only, the other being fixed to the 

 skin, or some other soft part, as, e. </., certain of the muscles of the 

 face, and those of the eyeball. Sometimes a muscle has no connec- 

 tion with bone whatever, as the little muscle in the palm (palmaris 

 brevis), and the orbicularis muscle which surrounds the mouth. In 

 the case of a muscle attached to bone by one end only, that attach- 

 ment is called its origin, the other being termed its insertion ; in the 

 case of muscles attached at both ends to the bones, that attachment 

 which is nearer to the centre of the body, and which is also usually 

 the more fixed point, is called the origin, whilst the more distant, usu- 

 ally the more movable, attachment, is named the insertion. Muscles 

 may have two points of origin, or heads (biceps of the arm), or three 

 (triceps), or many (great serratus) ; and, again, some muscles have 

 more than one point of insertion (flexors of the fingers and toes). 

 Muscles sometimes pass from bone to bone, over only one joint (del- 

 toid), but often they pass over two (biceps), or more joints (flexors of 

 fingers and toes, and long muscles of trunk). Tendons of origin of 

 muscles, that is, tendons by which they arise, are usually broad ; 

 whilst tendons of insertion are generally long and roundish. The 

 tendons of origin enable a large number of muscular fibres to act from 

 a given point of the skeleton ; whilst the tendons of insertion transmit 

 the muscular force to some other, and equally precise, point of bone ; 

 hence, they are inextensible, and inelastic. By means of the tendons, 



