THE MUSCULAR SYSTEM. 



.'I? 



Fig. 9G. 



Fine elastic fibres (the so-termed nuclear fibres) occur in the 

 secondary fasciculi of all tendons, in various conditions of 

 development : sometimes as a series of slender fusiform cells 

 connected by delicate processes ; sometimes as fully-formed 

 fibres of uniform thickness, or as isolated fusiform cells. The 

 arrangement of these elastic elements is uniform throughout, 

 and they run at regular distances, parallel to, and among the 

 fasciculi of connective tissue. Consequently, in the transverse 

 section of a tendon, the dark ends of the elastic fibres are 

 apparent, distributed, at constant distances of 0-007 — O'OOS'" 

 apart, over the whole section. But besides these stronger 

 elastic filaments, measuring from 0-0005 — 0-001'", there exist 

 in most, perhaps in all tendons, extremely delicate fibrils of 

 0-0002 — O-OOOi'", connecting the former in various directions, 

 so that in reality there is, in every 

 tendon, an elastic network, pene- 

 trating and entwining the fasci- 

 culi of connective tissue. These 

 fibrils may also be distinguished 

 on a transverse section, as minute 

 dark points, or as lines radiating 

 from the coarser points exhibited 

 in the section (fig. 96) ; and they 

 are still more evident in lon- 

 gitudinal sections, in which more 

 especially, the whole of the fibrous 

 system just described comes very 

 readily into view. In such sections, also, it is evident that, in 

 every case, in which the formative cells of which the fibres are 

 constituted still retain a certain degree of independence, very 

 distinct elongated nuclei exist in them. Besides these elastic 

 fibres, the tendons, in certain situations, contain cartilage-cells 

 (vid. infra), as well as common fat-cells, particularly in the more 

 lax tendons, as in the tendinous fibres of the intercostal muscles, 

 of the triangularis stemi, masseter, &c. 



The transversely banded aspect of the tendons, to which their 

 glistening appearance is due, depends simply upon the numerous 



Fig. 96. Tendon of the tibialis posticus, Man, x 60 diani.: a, secondary fasciculi; 

 b, thicker nuclear fibres ; c, interstitial connective tissue. 



