306 THE MUSCULAR SYSTEM. 
stratum, asin the limbs, or from the fusion of segmental elements (myotomes), as in 
the case of the axial muscles; the peripheral nerves supplying skeletal muscles are 
distributed, through the plexuses or directly, so as to associate particular muscles 
morphologically and physiologically, and to secure a co-ordinated movement by the 
simultaneous contraction of several muscles together. 
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 the fact that, except 
beneath the skin of the eyelids, penis, and scrotum, it is always more or less 
impregnated with fat. It is traversed by the cutaneous vessels and nerves; and 
its deep surface, membranous in character, is in loose connexion with the subjacent 
deep fascia. 
Deep Fascia. — Underneath the skin and superficial fascia is a fibrous 
membrane, bluish-white in colour, devoid of fat, and in closest relation 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 a special 
tendency to become attached to all subcutaneous bony prominences, and to be 
continuous with the connecting ligaments. It forms septal processes, which 
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 case 
of annular ligaments, bind down the tendons passing over the joint. It not only 
ensheathes vessels and nerves, but is also perforated by those which pass between 
superficial 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. vertebral 
aponeurosis) performs at one and the same time the purpose of a deep fascia and 
the expanded membranous attachment of a muscle. 
Burse.—Where a tendon passes over a bony surface, or where the superficial 
fascia and skin cover a bony prominence, there is generally formed a 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 synovial sheaths 
which envelop tendons beneath the annular ligaments in relation to the several 
joints. 
Description of Muscles.—In studying the muscular system it 1s necessary to 
note the following characters in reference to each muscle:—(1) The shape of the 
muscle—flat, cylindrical, triangular, rhomboidal, etc.—and the character of its 
extremities—membranous, tendinous, or fleshy. (2) The attachments of the muscle. 
The origin is the more fixed or central attachment: the ¢nsertion is the more mov- 
able or peripheral attachment. (3) The relations of the surfaces and borders of the 
muscle to bones, joints, other muscles, and other important structures. (4) Its” 
vascular and nervous supply ; and (5) its action. It must be borne in mind that 
hardly any single muscle acts alone. Each muscle, as a rule, forms one of a group 
acting more or less in harmony with, and antagonised by, other and opposite 
groups. 
The muscles of the body are separable histologically into two great divisions, 
according to the character of the muscle-cells. Striated muscle fibres constitute 
the whole of the skeletal muscles. Non-striated muscle fibres are characteristic of 
the muscular system of the viscera and vessels. The heart is composed of a striated 
muscular structure of a peculiar kind. Only the striated, skeletal muscles are 
described in this section. 
The skeletal muscles may be divided into two series: axial and appendicular. 
The axial muscles comprise the muscles of the trunk, head, and face, including 
the panniculus carnosus (platysma myoides). These muscles are more or less 
segmental in arrangement, grouped around the axial skeleton. The appendicular 
muscles, the muscles of the limbs, are grouped around the appendicular skeleton. 
They are not definitely segmental in arrangement, are clearly separate from the 
axial muscles, and are arranged in definite strata in relation to the bones of the 
limbs. 
