458 



HUMAN ANATOMY. 



maximus, the muscles are conspicuous on account of their coarse texture ; a fine- 

 grained muscle, on the contrary, is composed of small fasciculi. In addition to 

 variations in the thickness of the fasciculi, the latter differ greatly in length irrespec- 

 tive of the extent of the entire muscle, since the length of the fasciculi depends largely 



upon the arrangement of the ten- 

 FiG. 474. 



^ 





^ 

 ^ 



y 



^rC: 







^ 



{ 



;-r^ 







r?]^ 



k3i 



Perimysium l^f^^^^, , "^ ^^>^^^i n^ ' 





dons. A long muscle may be 

 composed of short fasciculi, since 

 the latter may be attached to ten- 

 dons which cover its opposite 

 sides or extend within its sub- 

 stance as septa. In such cases, 

 as in the rectus femoris or the 

 deltoid, the short fasciculi run 

 obliquely, thereby producing a' 

 pennate arrangement which often 

 characterizes muscles of great 

 strength. When, on the con- 

 trary, the tendons are limited to 

 the ends of a muscle, the fascic- 

 uli are relatively long and may 

 extend its entire length. The 

 sartorius contains fasciculi, as 

 well as fibres, of conspicuous ex- 

 tent, some bundles stretching 

 the entire distance between the 

 tendons. 



General Structure of 

 Striated Muscle. — The histo- 

 logical unit of voluntary muscular 

 tissue is the transversely striated 

 or striped nmscle-fibre, which 

 represents a highly specialized 

 single cell. The fibres are the 

 contractile elements by the shortening of which the length of the entire muscle is 

 decreased and the force exerted. The fibres are cylindrical, or prismatic with rounded 

 angles, in form, and vary from .01- i mm. in diameter ; no constant relation exists 

 between the thickness of the fibres and the size of the muscle of which they are the 

 components, and, indeed, their diameter varies even within the same muscle. In 

 general the limb muscles are composed of large fibres, those of the mature male sub- 

 ject usually exceeding the corresponding fibres of the female. The length of the 

 muscle-fibres is likewise subject to great variation. As a rule, the fibres composing 

 a muscle are of limited length, generally not exceeding from 4-5 cm. ; in exceptional 

 instances, however, as in the sartorius, they may attain a length of over 12 cm. and 

 a width of from 1-5 mm. (Felix). The fibres 

 are usually somewhat spindle-shaped, being 

 slightly larger in the middle than at the ends, 

 which are usually more or less pointed ; blunted 

 or club-shaped and, more rarely, branched ex- 

 tremities are not uncommon. Branched and 

 anastomosing fibres occur in certain localities, 

 as in the tongue, facial and ocular muscles. 



The individual fibres, each invested in its 

 own sheath, or sarcolemvia, are grouped into 

 small primary bimdles, the component fibres of 

 which are held together by a meagre amount of 

 connective tissue, the endomysium. The latter is continuous with the perimysium 

 investing the primary bundles. These are associated into uncertain groups, the 

 secondary bundles, which are united and enclosed by extensions and subdivisions of 

 the general connective-tissue envelope of the entire muscle, the epimysium. In muscles 



Muscle-fibres' 



m / 



Several primary muscle-bundles in transverse section, showing the 

 arrangement of component fibres. X 40. 



Fig. 475. 



Sarcoleninia 



Portion of muscle-fibre, showing sarcolemma 

 bridging break in sarcous substance. X 37°- 



