PHYSIOLOGY OF MUSCLE. 271 



with the fibrine of the blood, being made up of about seventy- 

 seven parts water, fifteen and a half parts fibrine, and seven and a 

 half parts of fixed salts. The whole of the flesh of the body is 

 largely supplied with blood, and it is found by experiment, on the 

 one hand, that if this is cut off contraction ceases very speedily 

 after ; and on the other, that in proportion to the amount of mus- 

 cular action will be the demand for fresh supplies of blood. None 

 of the striated muscles, except of the heart and the muscles of 

 respiration, can go on acting without intervals of rest, during 

 which, repairs in their structure are effected. If, therefore, the 

 voluntary muscles are to be brought into the highest state of vigor 

 and development of size, they must be regularly exercised and 

 rested at proper intervals. During the former condition blood is 

 attracted to them, and at the same time that fluid itself is ren- 

 dered more fit for the purposes of nutrition ; while, during the 

 latter period, the increased flow of blood continuing allows for a 

 complete reparation of the tissues. Thus we find the muscles of 

 the well-trained racehorse full and firm to the touch ; but if suffi- 

 cient intervals of rest are not allowed between his gallops, they 

 will present a very different feel, being flabby and wasted, and in- 

 dicating that he has been " overmarked." 



The voluntary muscles assume various shapes, according to 

 their positions and offices. Sometimes they are merely long strips 

 of muscular tissue, with a very short tendon at each end, as in the 

 levator humeri, and are then called fusiform. At others their 

 fibres radiate as in the latissimus dorsi, which is thence called a 

 radiating muscle. A third set are called penniform, from their 

 fibres being attached to one side of a tendon, or bipenniform, when 

 they are fixed to both sides like the full tail or wing feather of a 

 bird. A muscle with two masses of its tissue connected in the 

 middle by a tendon is called digastric. 



In describing each muscle, it is usual to speak of it as having 

 an origin from one bone, or set of bones, and an insertion into 

 another, the former term being generally assigned to the more 

 fixed division of the two. This is, however, merely for the sake 

 of convenience, and is entirely arbitrary. 



Burs^e Mucosa, which are shut sacs, varying in size from that 

 of a pea to a moderate pear, and lined with synovial membrane, 

 are placed on all the prominent points of bone over which tendons 

 glide. Thus there is a large one on the point of the hock, and 

 another on the elbow, both of which sometimes inflame and 

 become filled with synovia, constituting the states known as 

 capped hock and elbow. A third situation is just above the 

 sesamoid bones, where the swelling from inflammation receives the 

 name of windgall. Where, as in the legs, the tendons have to 

 glide to a great extent, they are invested with synovial sheaths, 



