TENDON-SHEATHS. 63 



muscle is attached to the skin, the radiating muscle-fibres are continued by 

 tendon-bundles of connective tissue rich in elastic fibres, an arrangement well 

 adapted to distribute evenly the pull of the muscle upon the integument. 



FIG. 81. Developing muscle-fibres in which the striation Is just appearing. X 375. 



The aponeuroses correspond in structure closely with the tendons, 

 being composed of parallel bundles of dense fibrous tissue which are arranged 

 to form membranous structures. 



The fasciae consist of feltworks of bundles of white fibrous tissue with 

 a variable, usually considerable, proportion of elastic fibres. Where very 

 dense, as in the fascia lata, they somewhat resemble tendon-tissue, the com- 

 ponent bundles of fibro-elastic tissue being com- 

 pactly disposed, although interwoven and lacking 

 in uniform placing, and containing little fat. The - / 



superficial fasciae, on the other hand, consist of I 



loosely felted fibro-elastic strands and ordinarily 

 support considerable, at times inordinate, masses t ' 



of adipose tissue. Where the fascia serves as a 

 muscle-sheath, it contains little fat but an unusual / 



number of elastic fibres, by virtue of which it 

 accommodates itself to the changing form of the 

 enclosed muscular tissue. 



Tendon-sheaths. Where tendons play in 

 bony grooves, or where it is necessary to overcome 

 some tendency to displacement, they are bound 

 down and held in place by bands of dense fibrous 

 tissue, which either convert the grooves into canals 

 or form tubular investments that enclose the ten- 

 dons, although allowing free longitudinal move- 

 ment. These connective tissue envelopes constitute 

 the tendon- sheaths and may surround more than 

 one tendon. Each sheath consists of an outer 



fibrous tunic (vagina fibrosa) composed of dense ^^f^A SPttS 

 fibro-elastic bundles, continuous with the perios- muscle-fibres, x *. 

 teum at the margins of the groove, and an inner 



synovial tunic (vagina mucosa), which lines the deeper surface of the 

 fibrous sheath and at the ends, or next the bone, is reflected, onto the 

 tendon. The latter, therefore, is more or less completely surrounded by 

 a double-walled cylinder, whose cavity is filled with a fluid serving to 

 diminish friction during the play of the tendon. The synovial tunic 

 resembles the lining of joint-cavities, being clothed with an imperfect layer 

 of endothelial plates. In the larger sheaths, minute vascular projections 

 recall the synovial villi. 



