98 NORMAL HISTOLOGY. 



" sarcous elements," which are arranged end to end to form eol- 

 umns, sarcostyles, extending parallel to eaeh other, from one end 

 of the cell to the other. The sarcous elements of all the sarcostyles 

 lie in planes perpendicular to the long axis of the cell. It is r 

 therefore, possible to separate the contractile substance into a 

 number of fibre-like columns (sarcostyles, Fig. 67), made up of sar- 

 cous elements attached at their ends, or to split it transversely into 

 disks composed of sarcous elements lying side by side. Between 

 the sarcous elements is a substance which has received the name 

 " sarcoplasm." 



The contractile substance is enclosed in a thin, homogeneous mem- 

 branous envelope, called the " sarcolemma." The nuclei of the cell lie 

 immediately beneath the sarcolemma, between it and the contractile 

 substance, and are surrounded by a small amount of unmodified 

 cytoplasm. 



The muscle-fibres lie parallel to each other and to the general 

 direction of the muscle which they compose, and are separated by 

 loose areolar tissue, containing their vascular and nervous supplies. 

 The areolar tissue between the individual muscle-fibres is called the 

 endomysium and supports an abundant network of capillary blood- 

 vessels lying parallel to the fibres with numerous transverse anas- 

 tomoses. Broader septa of areolar tissue divide the whole muscle 

 into fasciculi and support the larger bloodvessels and nerves. These 

 septa are collectively known as the perimysium. Surrounding the 

 whole muscle and continuous with the perimysium and endomysium 

 is a thicker sheath of fibrous tissue, the epimysium. When seen in 

 noss-section the muscle-fibres are circular or polygonal in form, and 

 the cut surface of the contractile substance appears crowded with 

 small polygonal areas, the sections of the sarcous elements, between 

 which is the sarcoplasm. Where the nuclei are included in the sec- 

 tion they appear somewhat flattened and lie at the edge of the con- 

 tractile substance, where a thin zone of cytoplasm may sometimes 

 be detected around them. The sarcolemma which lies outside of these 

 constituents of the cell is so thin that it can rarely be distinctly seen. 



The muscle-fibres are in close contact at both ends with the dense 

 fibrous tissue of the tendons attached to the muscle, or with the peri- 

 osteal fibrous tissue when the muscle appears to be attached directly 

 to bone — e. g., the scapula. In most of the voluntary muscles 

 there are occasional groups of small fibres which differ in structure 

 from the majority and appear to be subordinate to and certainly 



