272 



round the bones of the extremities. They vary 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 situation, 

 and others from their use, and thus we have abductors and adductors, 

 the pyramidal and orbicular, the digastricus, the vastus, and the rest. 

 Those which are under the control of the will, known as the voluntary 

 muscles, appear in the form of fleshy 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 tissue, each fasci- 

 culus being composed of smaller ones, less in size, but united in a simi- 

 lar manner to compose the larger formations, each of which is enveloped 

 by a structure of similar nature known as the sarcolemma. Many of 

 the muscles are united to the bones by 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 membranous structure known 

 as the tendon or sinew, and the attachment is made by very 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 fiir 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 themselves or formed at their 

 articulations, and this need is supplied by the secretion of the synovial 

 fluid, a yellowish, unctuous substance, furnished by a peculiar tendin- 

 ous synovial sac, designed for the purpose. 



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

 the sliding movements of the tendons may be found under their various 

 forms at the shoulder joint, at the upper part of the bone of the arm, 

 at the posterior part of the kneejoiut, and also at the fetlocks, on their 

 posterior part. 



As the tendons, whether singly or in company with others, pass over 

 these natural puUies 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 important special 

 use as supports and reenforcements of the tendons themselves, with 

 which they must necessarily share the stress of whatever force or strain 

 is br>)Ught 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 form a joint or articulation, either mov- 

 able or fixed, and a concise examination of the formation and structure 

 of the movable articulations will here be in place. These are formed 

 generally by the extremities of the long, or they may exist on the sur- 

 faces of the short bones ; the points or regions where the contact oc- 

 curs being denominated the articular surface, which assumes from this 

 circumstance a considerable variety of aspect and form, being in one 

 case comparatively flat and at another elevated ; or as forming a pro- 



