MYOLOGY 



^Myology deals with the muscles and their accessory structures. The muscles 

 ([Nlusculi) are highly specialized organs, which are characterized by their property 

 of contracting in a definite maimer when stimulated. They are the active organs 

 of motion. The contractile part of the muscle is the muscxilar tissue. Three kinds 

 of muscular tissue are recognized, viz.: (1) Striated or striped; (2) non-striated, 

 unstriped or smooth; (3) cardiac, which may be regarded as a specialized variety 

 of striated muscle. Only the first of these will be considered in this section. The 

 striated muscles are for the most part connected directly or indirectly with the 

 skeleton, upon which they act, and are hence often designated as skeletal muscles 

 (]\lusculi skeleti), in distinction from non-striated muscle, which is often spoken 

 of as visceral. The striated muscles cover the greater part of the skeleton, and play 

 an important part in determining the form of the animal. They are red in color, 

 the shade varying in different muscles and under various conditions. Some are in- 

 timately associated wdth and attached to the skin, and are called cutaneous mus- 

 cles (Musculi cutanei). The muscular part of each is composed of bundles of con- 

 tractile fibers surrounded by a thin sheath of connective tissue, the perimysitmi. 



The description of the muscles may be arranged under the following heads : (1) 

 Name; (2) shape and position; (3) attachments; (4) action; (5) structure; (6) 

 relations; (7) blood and nerve supply. 



(1) The name is determined by various considerations, e. g., the action, at- 

 tachments, shape, position, direction, etc. In most cases two or more of these are 

 combined to produce the name, e. g., flexor carpi radialis, longus colli, obliquus 

 externus abdominis. 



A satisfactory comparative nomenclature is exceedingly difficult to work out, and much 

 confusion exists in this respect. This is due in great part to the lack of a uniform basis for the 

 foiTuation of names and the difficulty in determining homologies in various species. 



(2) The shape is in many cases sufficiently definite and regular to allow the 

 use of such terms as triangular, quadrilateral, fan-shaped, fusiform, etc. Some 

 muscles are characterized as long, broad, short, etc. Orbicular or ring-like muscles 

 circumscribe openings; since the contraction of such a muscle closes the orifice, it is 

 often termed a sphincter. The position and direction are usually stated with refer- 

 ence to the region occupied and to adjacent structures which may be presumed to be 

 already known. 



(3) The attachments are in most cases to bone, but many muscles are attached 

 to cartilage, ligaments, fascia, or the skin. As a matter of convenience, the term 

 origin (Origo) is applied to the attachment which always or more commonly re- 

 mains stationary when the muscle contracts; the more movable attachment is 

 termed the inseri:ion (Insertio). Such a distinction is often quite arbitrary, and 

 cannot always be made, as the action may be reversible or both attachments may be 

 freely movable. With respect to the muscles of the limbs, the proximal attachment 

 is regarded as the origin and the distal one as the insertion. In all cases the attach- 

 ment is made by fibrous tissue, the muscular tissue not coming into direct relation 

 with the point of attachment. But when the intermediate fibrous tissue is not evi- 

 dent to the naked eye, it is customary to speak of a "fleshy attachment.'.' The 

 term "tendinous attachment" is applied to those cases in which the intermediate 

 fibrous tissue — tendon or aponeurosis — is evident. A tendon (Tendo) is a band of 



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