364 THE MUSCULAE SYSTEM. 



the thigh, the muscles of the back, and the prevertebral muscles, groups in whicl 

 separate muscles are associated together by development, nerve-supply, and action 

 In their development the separate muscles arise from the subdivision of a large: 

 stratum, as in the limbs, or from the fusion of segmental elements (myotomes), as ii 

 the case of the axial muscles. The peripheral nerves supplying skeletal muscles art 

 distributed, through the plexuses or directly, so as to associate particular musclei 

 morphologically and physiologically, and to secure a co-ordinated movement by th< 

 simultaneous contraction of several muscles. 



FASCIJE. 



Beneath the skin there are two (or in some regions three) layers of tissue whicl 

 require consideration in relation to the muscular system: the superficial fascia 

 (panniculus adiposus), the deep fascia, and, in animals, the panniculus carnosu! 

 (rudimentary in man, and represented chiefly by the platysma in the neck). 



Fascia Superficialis (Superficial Fascia). The superficial fascia is a continuous 

 sheet of areolar tissue which underlies the skin of the whole body. It is closely 

 adherent to the cutis vera, and is sometimes termed panniculus adiposus, from th( 

 fact that, except beneath the skin of the eyelids, penis, and scrotum it is usuall] 

 more or less impregnated with fat. The cutaneous vessels and nerves ramify ii 

 this fascia ; and its deep surface, membranous in character, is in loose connexioi 

 with the subjacent deep fascia. It is in this layer that dropsical effusions chiefly 

 occur. 



Fascia Profunda (Deep Fascia). Underneath the skin and superficial fascia 

 is a fibrous membrane, bluish white in colour, devoid of fat, and in closest relatior 

 to skeleton, ligaments, and muscles. This is the deep fascia. It covers, invests 

 and in some cases forms the means of attachment of the various muscles. It has 

 special tendency to become attached to all subcutaneous bony prominences, anc 

 to be continuous with the connecting ligaments. It forms septal laminae, whicl: 

 separate groups of muscles and individual muscles; enclose glands and viscera 

 and form sheaths for vessels and nerves. Around joints it gives rise to bands 

 which strengthen the capsule or limit the mobility of the joint, or, as in the region 

 of the wrist and ankle, bind down the tendons passing over the joint. It not onlj 

 ensheathes vessels and nerves, but is perforated by those which pass between super- 

 ficial and deeper parts. 



The term aponeurosis is used in relation to muscles. It is synonymous with deep 

 fascia, either as an investing fascia, or as a membranous layer which (e.g. vertebra] 

 aponeurosis) performs at one and the same time the purpose of a deep fascia and 

 the expanded membranous attachment of a muscle. 



The panniculus carnosus is a thin muscular layer enveloping the trunk oi 

 animals with a hairy or furry coat. It is strongly developed in the hedgehog. In 

 man it is represented mainly by the (rudimentary) platysma. It is placed between 

 the superficial and the deep fascia. 



Bursae. Where a tendon passes over a bony surface, or where the superficial 

 fascia and skin cover a bony prominence, there is generally formed a mucous 

 (synovial) sac, or bursa, containing fluid, for the purpose of lubricating the surface 

 over which the tendon or fascia glides. Allied to these are the mucous or synovial 

 sheaths which envelop the tendons passing over the wrist and the ankle joints. 



Description of Muscles. In studying the muscular system it is necessary to 

 note the following characters in reference to each individual muscle : (1) The shape 

 of the muscle flat, cylindrical, triangular, rhomboidal, etc. ; and the character oi 

 its extremities membranous, tendinous, or fleshy. (2) The attachments of thei 

 muscle. The origin is the more fixed or central attachment : the insertion is the 

 more movable or peripheral attachment. (3) The relations of the surfaces anc< 

 borders of the muscle to bones, joints, muscles, and other important structures 

 (4) Its vascular and nervous supply ; and (5) its action. It must be borne in mine 

 that hardly any single muscle acts alone. Each muscle, as a rule, forms on 



