166 CONNECTIVE TISSUE. 



individuals, and afc the periphery of the bundles at any age, the 

 rows and chains are more numerous. The interstices between 

 the larger bundles contain, besides a few capillary blood-vessels, 

 a large number of nucleated plastids, either isolated or united in 

 a continuous layer. The sum total of these plastids, together 

 with a slight amount of basis-substance, constitutes what we 

 have called (see page 147) medullary tissue. In advanced age 

 the medullary corpuscles are much less numerous, and a loose 

 fibrous connective tissue carries the blood-vessels. Elastic fibers 

 are, as a rule, not present at the borders of the bundles. A 

 comparison between the plastids within and those between the 

 bundles shows them to be alike in size and general appearance, 

 with the only difference that those within the bundles are rela- 

 tively few in number, while those in the interstices are very 

 numerous. The view can, therefore, be maintained that between 

 the larger bundles there are numerous, and between the small 

 fasciculi, composing one bundle, there are few, plastids a view 

 which, as I shall later on demonstrate, proves useful for under- 

 standing the structure of the tendon as well as its development. 

 (See Fig. 60.) 



In the transverse section of a tendon we notice fields of basis- 

 substance very finely dotted, the dots being the transverse sec- 

 tions of the fibrilla?. In the bundles we recognize the granular, 

 usually nucleated, plastids or tendon corpuscles, with numerous 

 stellate offshoots, the " wings " of authors. Offshoots connect 

 the plastids with each other and with the medullary tissue, or 

 the loose fibrous connective tissue, present in the interfascicular 

 spaces. The smaller bundles do not usually show distinctly 

 marked outlines, as neighboring bundles frequently coalesce, and 

 are not separated by offshoots of the tendon corpuscles. When 

 we recall the spindle shape of each bundle, we can readily under- 

 stand why their sizes vary in transverse section. We may call 

 a bundle a field which is completely surrounded by interfascicular 

 tissue, and contains in its center a branching plastid, or, we may 

 say, a larger bundle is composed of a number of smaller ones, 

 though not distinctly separated, between which lie the branching 

 plastids. The blood-vessels are met with only in the interfas- 

 cicular spaces, running both in transverse and longitudinal direc- 

 tions ; they penetrate the tendon through the tenaculum, which 

 connects it with its sheath, and the elongations of which con- 

 stitute the interstitial formations between the tendon bundles. 

 (See Fig. 61.) 



