184 THE MUSCLES IN GENErwiL. 



thin, others are more or less elongated straps, and others are cylindrical 

 or fusiform masses of various thickness ; hence some of the various 

 names applied to them, such as long and short, square, round, rhomboid, 

 &c. Not uufrequently two or more muscular parts run into one, as in 

 the bicipital, tricipital, or quadricipital forms. In other instances 

 muscles, beginning as single masses, become divided, at their remote 

 ends, into two or more muscular tendinous slips. A division of a muscle 

 into two parts by an intermediate tendon gives the form called digastric 

 or biventral, and there arc some muscles in which a greater number of 

 parts are thus separated by what have been called tendinous inscrip- 

 tions. 



In the description of the muscles it is customary to state the attach- 

 ments of their opposite ends under the names of orijiin and insertion ; 

 the first term being usually applied to the more fixed, or in the case of 

 the limbs the proximal extremity, and the second to the more movable 

 or remote attachment ; but it is to be observed, that it is often diiR- 

 cult to lay down a rule for the correct use of these terms, and that in 

 the great majority of instances it is of importance to consider the 

 action of a muscle as it may affect the motions of the parts attached 

 not to one only but to lioth of its extremities. 



The study of the actions of the muscles either singly or in groups, 

 though strictly a physiological subject, cannot be separated from their 

 anatomical description. With respect to this the following general 

 principles ought to be kept in view. 1st. That the force exerted by any 

 muscle during its contraction is in proportion to the tivmher of mus- 

 cular elements or fibres composing the muscle. 2nd. That the extent 

 of motion, in so far as it merely depends on the shortening of the fibres 

 of the muscle, is in proportion to the Jcnuih of the fibres. And ord. 

 That the direction of the force produced by a contracting muscle 

 is in the line of the axis of the whole muscle if it run straight between 

 its opposite points of attachment, but in the line of the portion attached 

 to the moving part if the muscle or its tendon be bent in its course. In 

 most instances of such deflection from the straight course the muscles 

 or their tendons run in loops or in grooves somewhat after the manner 

 of a pulley. The loops are either fibrous or cartilaginous. In the 

 pulley -like disposition of tendons running over bones, there are fi'e- 

 quently fibrous or cartilaginous or bony nodules developed at the place 

 of angular bending of the tendons. The name sesamoid, originally 

 given to the small bones developed in some of the digital tendons, 

 has been applied generally to all similar intratendinous structures. 



It is further to be observed that the direction in which the muscular 

 fibres or fasciculi run in a muscle is very frequently not that of the axis 

 of the muscle, nor do the muscular fasciculi in the great majority of 

 instances extend from end to end in a muscle. On the contrary, the 

 muscular fibres and fasciculi are much oftener comparatively short, and 

 are attached within the length of the muscle to prolongations of the 

 main tendons or to other tendinous bands which intersect its substance ; 

 and thus the muscular fibres run into these tendinous parts with various 

 degrees of obliquity to the axis of the muscle. 



The muscular llesh forms a large proportion of the weight of the 

 whole body. This proportion has l)een carefully determined by mea- 

 surements recently published by Dr. G, v. Liebig (Archiv. fur Auat. u. 

 Physiol. 1874, p. 90), from whose tables the following is calculated 



