358 



THE MUSCLES AND FASCIA 



or perichondrium, and do not come into direct relation with the osseous or carti- 

 laginous tissue. Where muscles are connected with the skin, they either lie as 

 a flattened layer beneath it, or are connected with its areolar tissue by larger or 

 smaller bundles of fibres, as in the muscles of the face. The origin of a muscle 

 is its head (capuf), while the intermediate portion is called the belly, or venter. 

 The muscles vary extremely in their form. In the limbs they are of consider- 

 able length, especially the more superficial ones, the deep ones being generally 

 broad; they surround the bones and form an important protection to the various 

 joints. In the trunk they are broad, flattened, and expanded, forming the parietes 

 of the cavities which they enclose; hence the reason of the terms long, broad, 

 short, etc., used in the description of a muscle. 



There is a considerable variation in the arrangement of the fibres of certain 

 muscles with reference to the tendons to which they are attached. In some, the 

 fibres are parallel and run directly from their origin to their insertion; these are 

 quadrilateral muscles, such as the Thyrohyoid. A modification of these is found 

 in the fusiform muscles in which the muscle tapers at each end ; in their action, 



however, they resemble the quadrilateral muscles. 

 Secondly, in other muscles the fibres are con- 

 vergent; arising by a broad origin, they converge 

 to a narrow or pointed insertion. This arrange- 

 ment of fibres is found in the triangular muscles 

 e. g., the Temporal. In some muscles, which 

 otherwise would belong to the quadrilateral or 

 triangular type, the origin and insertion are not in 

 the same plane, but the plane of the line of origin 

 intersects that of their insertion ; such is the case 

 in the Pectineus muscle. Thirdly, in some muscles 

 the fibres are oblique and converge, like the 

 plumes of a pen, to one side of a tendon, which 

 runs the entire length of the muscle. Such a 

 muscle is penniform (ra. unipennatus), as the 

 Peronei. A modification of these muscles is found 

 in those cases where oblique fibres converge to both 

 sides of a central tendon which runs down the 



middleof the muscle;these are called bipenniform (m. bipennatus^and an example is 

 afforded in the Rectus femoris. Multipennate muscles are those in w r hich the muscle 

 fibres alternate with a series of tendinous bands, as in the Deltoid. Biventral 

 muscles occur, such as the Digastric, while the Rectus abdominis shows subdivision 

 into four or more sections by intervening inscriptiones tendineae. Certain muscles 

 do not act in a direct manner, for they or their tendons pass around a bony pro- 

 jection or through a septal pulley (trochlea). Finally, we have muscles in which 

 the fibres are arranged in curved bundles in one or more planes, as in an orbicular 

 muscle and in that variety of orbicular muscle called a sphincter muscle. The 

 arrangement of the muscle fibres is of considerable importance in respect to their 

 relative strength and- range of movement. Those muscles in which the fibres are 

 long and few in number have great range, but diminished strength; where, on 

 the other hand, the fibres are short and more numerous, there is great power, 

 but lessened range. 



Muscles differ much in size; the Gastrocnemius forms the chief bulk of the 

 back of the leg; the Sartorius is very long; the Stapedius, a small muscle of the 

 internal ear, weighs about a grain, and its fibres are not more than 4 mm. in 

 length. 



The names applied to the various muscles have been derived (1) from their 

 situation, as the Tibialis, Radial is, Ulnaris, Peroneus; (2) from their direction, as 



Humerus. 



FIG. 286.- Diagram of the Deltoid, an 

 example of a multipennate muscle. 



