STRUCTURE OF THE MUSCLES. 



409 



Fig. 262. 



ligaments, and containing very few elastic fibres. The fasciculi of 

 the collagenous tissue are inclosed in sheaths of areolar tissue, which 

 thus forms delicate dissepiments penetrating the substance of the 

 tendons, as shown in Fig. 261 ; then several of the primary fasciculi 

 (five to ten) are collected into large bundles the secondary fasci- 

 culi. Finally, the vessels are distributed in the spaces between the 

 fasciculi (Fig. 176); elastic fibres are also sent into them, and the 

 whole is invested by a sheath of areolar tissue (p. 278, 1). 



The elastic fibres require a particular description, however. In 

 a transverse section of a tendon, their extremities are seen as dark 

 points in the substance of the fasci- 

 culi, at constant distances of T7 'uTj to 

 iVsff f an i ncn apart, over the whole 

 section; and being ^J^ to T2 J^ 

 of an inch in diameter. (Fig. 262.) 

 These are also connected together in 

 various directions by other finer 

 fibres, ^Jjfl to ^J^ of an inch in 

 diameter, so that there is in tendons 

 an elastic network penetrating and 

 entwining the collagenous tissue. 

 These are sometimes seen in trans- 

 verse sections, as lines radiating from 

 the coarser points before mentioned. 



Besides, the tendons in certain 

 situations contain cartilage-cells, as 

 well as even fat-cells as in the intercostal muscles, the masseter, &c. 



The glistening appearance of the tendons depends upon their 

 transversely banded aspect, as seen under the microscope ; and the 

 latter is produced by the numerous curves in the fibres, which cor- 

 respond with each other throughout the fasciculus. The curves are 

 doubtless produced by the elastic tissue in the fasciculus, and there- 

 fore at once disappear when the tendon is stretched. 



The tendons consist of 62.03 per cent, of water (ChevreuiJ)] they 

 containing considerably less, therefore, than the muscular tissue 

 (p. 396). 



3. The belly of the fusiform muscles, and the red portion of all 

 others, is the only portion that presents a peculiar structure, as 

 alone containing the muscular tissue; and this, therefore, will be 

 particularly described. It consists of 



Tendon of the tibialis posticus (man). 

 a. Primary fasciculi. &. Thicker nucleated 

 fibres, e. Interstitial connective tissue. 

 Magnified 60 diameters. (Kottiker.) 



