282 



surround the bones of the extremities. They varj' greatly in shape and 

 size, being flat, triangular, long, short, or broad, and are variously 

 and capriciously named, some from their shape, some from their situa- 

 tion, and others from their use, and thus we have abductors and adduc- 

 tors, the pyramidal and orbicular, the digastricus, the vastus, and the 

 rest. Those which are under the control of the will, known as the vol- 

 untary muscles, appear in the form of flesh}^ structures, red in color, 

 and with fibers of various degrees of fineness, and are composed of 

 ^fasciculi,'''' or bundles of fibers, united by connective or cellular tis- 

 sue, each fasciculus being comiDosed of smaller ones, less in size, but 

 united in a similar manner to compose the larger formations, each of 

 which is enveloped by a structure of similar nature known as the sar- 

 colemma. Many of the muscles are united to the bones b}- the direct 

 contact of their fleshy fibers, but, in other instances, the body of the 

 muscle is more or less gradually transformed into a cordy or mem- 

 branous structiire kno^vn as the tendon or sinew, and the attachment 

 is made by ver}^ short fibrous threads through the medium of a long 

 tendinous band, which, passing from a single one to several other of 

 the bones, effects its object at a point far distant from its original 

 attachment. In thus carrying its action from one bone to another, or 

 from one region of a limb to another, these tendons must necessarily 

 have smooth surfaces over which to glide, either upon the bones them- 

 selves or formed at their articulations, and this need is supplied by 

 the secretion of the synovial fluid, a yellowish, unctuous substance, 

 furnished by a jieculiar tendinous synovial sac, designed for the 

 purj)ose. 



Illustrations in point of the agency of the synovial fluid in assisting 

 the sliding movements of the tendons may be found under their vari- 

 ous forms at the shoulder joint, at the upper x)art of the bone of the 

 arm, at the posterior part of the knee joint, and also at the fetlocks, 

 on their posterior part. 



As the tendons, whether singl}' or in company with others, pass 

 over these natural pulleys they are retained in place by strong fibrous 

 bands or sheaths, which are by no means exempt from danger of 

 injury, as will be readily inferred from a consideration of their impor- 

 tant special use as sujaports and reenforcements of the tendons them- 

 selves, with which they must necessarily share the stress of whatever 

 force or strain is brought to bear upon both or either. 



"We have referred to that special formation of the external surface 

 of a bone by which it is adapted to forma joint or articulation, either 

 movable or fixed, and a concise examination of the formation and 

 structure of the movable articulations will liere be in place. These 

 are foi-med generally by the extremities of the long, or they may 

 exist on the surfaces of the short bones; the points or regions where 

 the contact occurs being denominated the articular surface, which 

 assumes from this circumstance a considerable variety of aspect and 



