390 HAL DOWNEY 



mis. The tendon fibers stain darker than the smallest fibers 

 found in other parts of the epiderm, but not any darker than 

 thick bundles of fibers (fig. 1). Where the tendon fibers are 

 frayed out at the ends the staining reactions of their fine consti- 

 tuent fibrils are identical with those of fibrils in other parts of 

 the hypoderm. It is probable, therefore, that the dark staining 

 of the tendon fibers is due to their density, rather than to changes 

 in their chemical nature. 



A condition similar to that described above is seen also at the 

 inner ends of the tendon fibers, where they are attached to the 

 muscles (figs. 1, 3, 5). The fine inner branches resulting from the 

 division of the coarser fibers into their constituent fibrils may fol- 

 low a comparatively straight course, as in figure 3, or they may 

 anastomose freely with neighboring fibrils at the lower border of 

 the tendon, as in figure 5. The latter condition may produce a 

 more or less horizontal layer or network of fibers composed of anas- 

 tomosing branches of the tendon fibers (fig. 5) . Such a structure 

 might easily be mistaken for a basement membrane. Fibrils 

 from the surrounding epidermal regions, and probably also from 

 the supporting tissue, usually join with the branches of the tendon 

 fibers in the formation of this layer (fig. 1). However, this is 

 probably not the case in the region shown in figure 5, and certainly 

 not in the parts shown in figure 3. The latter figure shows that 

 a horizontal layer of fibers may be absent at the point of attach- 

 ment of the muscle to its tendon, but even in this case there is 

 more or less branching of the finer fibrils at their inner ends. 



The exact mode of attachment of the muscles to their tendons 

 is shown in figures 1, 3, and 5. In figures 1 and 3 we see that the 

 fine branches of the tendon fibers are continued down into the 

 muscle for a variable distance, and that the muscle fibrils run up 

 between these processes. Figure 1 also shows that fibers from the 

 horizontal layer which are derived from other regions of the hypo- 

 dermis may penetrate the muscle for some distance. The long 

 fiber on the right of the figure is probably derived from this source. 

 There are no horizontal fibers in the greater part of figure 3, and 

 therefore the muscle attachment here is entirely by means 

 of fine branches of the tendon fibers. In figure 5 most of the fibrils 



