200 THE MUSCLES IN GENERAL. 



and the whole muscle is enclosed in an external sheath of the same material the 

 epimysium (Schafer). Many of the muscles are connected at their more or less 

 tapering extremities with tendons by which they are attached to the bones or hard 

 parts ; and tendinous bands frequently run to a considerable length either on the 

 surface of a muscle or between its fibres. There is indeed great variety in the rela- 

 tion of the muscular and tendinous portions, and but few muscles are entirely 

 destitute of some tendinous element in their composition. 



Farther, blood-vessels are largely distributed in the substance of a muscle, carry- 

 ing the materials necessary for its nourishment and chemico- vital changes, and 

 there are also lymphatic , vessels, at least in the perimysium and the tendons. 

 Nerves ramify through every muscle, and by means of these the muscular con- 

 tractions are called forth and a low degree of sensibility is conferred upon the 

 muscular substance. 



The muscles vary much in their individual forms. Some are broad and 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 unfrequently 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 or tendinous slips. A division of a 

 muscle in its length into two parts by an intermediate tendon gives the form called 

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

 parts are thus separated by what are called tendinous inscriptions or intersections. 



In the description of the muscles it is customary to state the attachments of their 

 opposite ends under the names of origin 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 moveable or distal attachment ; but it is often difficult to 

 lay down a rule for the correct use of these terms, and 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 both 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 number 

 of muscular 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 length of the fasciculi. And 3rd. 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 fibro-cartilaginous. In the pulley-like disposition of 

 tendons running over bones, there are frequently fibrous or cartilaginous or bony 

 nodules developed at the place of 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 farther to be observed that the direction in which the muscular fasciculi 

 run in a muscle is very frequently not that of the axis of the muscle, nor do they 

 in the great majority of instances extend from end to end in a muscle. On the 

 contrary, the muscular fasciculi are much ofbener comparatively short, and are 

 attached within the length of the muscle to prolongations of the main tendons or 



