THE MUSCULAR SYSTEM 



MYOLOGY 



The muscles (Musculi) are the active organs of motion. They are charac- 

 terized by their ])roperty of contracting when stimulated. Muscular tissue is of 

 three kinds: (a) Striated or striped; (5) non-striated, unstriped, or smooth; and 

 (c) cardiac. Only the first of these varieties will be considered in this section. The 

 striped muscles, being for the most part directly or indirectly connected with the 

 skeleton, are often termed skeletal or somatic, while unstriped muscle may be spoken 

 of as visceral or splanchnic. The former cover the greater part of the skeleton, 

 and thus in a large measure determine the form of the animal. They are red in 

 color, the shade varying in different muscles and under various conditions. 



Muscles vary greatly in form, and may be classified as — (o) Long; (6) short; 

 (c) flat; (rf) ring-like or orbicular. Long muscles are found chiefly in the limbs, 

 while the flat or l)road muscles occur principally in the trunk, where they assist in 

 forming the walls of the body cavities. The ring-like or orbicular muscles circum- 

 scribe orifices which they close, and are hence termed sphincters. 



Attachments. — The muscles are attached to bones, cartilages, Ugaments, 

 fasciae, or the skin. In all cases the attachment is by means of fibrous tissue, the 

 muscle-fibers not coming into direct relation with the bone or cartilage. The 

 perimysium of the muscle may fuse directly with the periosteum or perichondrium 

 (fleshy attachment), or the union may be by means of intermediary fibrous struc- 

 tures called tendons or aponeuroses (tendinous attachment). Tendons may be 

 funicular, riljbon-like, or in the form of membranous sheets; to the latter the term 

 aponeurosis is commonly applied. 



In certain positions, especially where tendons play over joints or are subjected 

 to great pressure, sesamoid bones develop in the original tendon tissue. Some 

 of these are large and constant, as the patella and the great sesamoids of the fet- 

 lock. 



The accessory structures connected with the muscles are the synovial mem- 

 branes and the fasciae. 



_Mesotenclon 



J^ibrous sheatk. 



'Synovial sheath 





Fig. 171. — Dt.\(:R.\M.s of Cross-sections of Tendon She.^th (A) and BrRS.\ (B); T, Tendon. 



The synovial membranes are arranged in two principal forms: (a) Bursal; 

 (6) vaginal. A bursa (Bursa mucosa) is a simple sac interposed between the tendon 

 or muscle and some deeper seated structure— most commonly a bony prominence. 

 A vagina tendinis or tendon sheath differs from a bursa in the fact that the synovial 

 sac is folded around the tendon more or less completely, so that two layers can be 

 distinguished; of these, the inner one adheres closely to the tendon, while the 

 outer lines the groove or canal in which the tendon lies. The two layers are con- 



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