6 4 



HISTOLOGY 



It will now be realized that the fibrils are not cellular elements, 

 but extra-cellular structures belonging to and elaborated by the cells 

 we have found lying among them. The cells present several odd and 

 extreme features by which they differ from a typical cell. The 

 nucleus is not spherical, but drawn out so that it appears in our 

 specimen like a bit of red thread and needs a high power to show 

 its nuclear organs. Again, the cytoplasm does not lie as a spherical 

 body around the nucleus, but is drawn out from it in three, four, or 

 five longitudinal and lateral plate-like projections, which have been 

 appropriately called " wings," leaving a very small proportion of the 

 cytoplasm immediately surrounding the nucleus. It also reaches for 

 a considerable distance beyond the two ends of the nucleus. 



The nucleus is long and thin because it must lie in the midst of fibrils 

 which, at frequent intervals, are under enormous strain. If spherical, 

 the nucleus would be crushed and would interfere with the efficiency 

 of the fibrils. The cytoplasm is drawn out in several directions because 

 it must be in contact with the fibrils to support them. It is drawn out in 

 the wing-like form because this form allows its duties to be performed 

 without injury to itself or interference with the work of the fibrils. It is 

 a manifest mechanical truth that a given number of fibrils all pulling 

 together should be placed parallel to each other and side by side for the 



greatest efficiency, and the call for 

 efficiency is so urgent in the highly 

 organized tendon that the cellular ele- 

 ments have to be modified to give the 

 fibrils every opportunity. 



The tendon we have examined is 

 not elastic to any degree, but will 

 break before it will stretch. This 

 condition is doubtless obtained by its 

 chemical composition and demanded 

 by its use. There are other connect- 

 ive-tissue cells, however, which form 

 tendons that will stretch. 



The ligamentum nuchae of an ox 

 or other mammal shows this struc- 

 ture (Fig. 66). Here the cells have a 

 different structure that produces an 

 elastic fibril in place of the non-elas- 

 tic fibril. This elasticity is further 

 developed by the net work- like ar- 

 rangements of the fibrils which are woven among each other and do 

 not lie parallel. The fibrils are very large and the nuclei of the cells 



. jj^ 



FIG. 66. Portion of ligamentum nuchae 

 of ox. conn.t.c., connective-tissue cells. 



