HIGHER TENSILE CONNECTING TISSUES 63 



Such tissue can also be found in many very low animals and the em- 

 bryos of most invertebrates. In vertebrate embryos, besides being under 

 the epidermis of the umbilical cord, it is found under the skin of the whole 

 body and among all the organs. 



Neuroglia, because of the form of its cells, might be placed in this class 

 of connective tissues. Because, however, of its association and common 

 origin with nervous tissues, we have placed it with the nervous tissues in 

 Chapter XIII. 



Technic. Carefully made sections fixed in most of the ordinary 

 fixatives will give good pictures of the cell elements. When it is desired 

 to see the extra-cellular fibrils, a fixative without acid must be selected. 

 Both paraffin and celloidin sections should be used. The stain can be a 

 special stain for the demonstration of the fibrils, as may be seen by 

 going over the stains for this purpose in LEE. Teasing has been of no 

 use for the study of these tissues. 



LITERATURE 



SPULER, A., 1897. " Beitrage zur Histologie und Histogenese der Bind- und Stutzsub- 

 stance," Anal. Hefte, 1897, p. 115. 



conn. t. c. 



THE SUPPORTING AND CONNECTIVE TISSUES: SPECIALIZED 

 TENSILE FORMS 



It is right to decide the degree of special- 

 ization of a tissue by the degree to which its 

 characteristic features are developed either quan- 

 titatively or qualitatively. Thus we may exam- 

 ine, as a specimen of highly specialized tensile 

 connective tissue, the tendon connecting a muscle 

 with a bone in a mammal or bird (Fig. 65). 



The first impression one receives on looking 

 at a longitudinal section of tendon is a great 

 amount of fine, strong, parallel strands in which 

 no nucleus is present. Nuclei can be seen, 

 however, between the fibrous strands; and a 

 closer inspection, especially in transverse sec- 

 tions, will disclose the cytoplasm belonging to 

 each nucleus, wedged in between the fibrils and, 

 like them, drawn out extensively in the direction 

 of the fibrils. The entire surface of the cyto- 

 plasm is in contact with some fibrils. In turn 

 each fibril throughout its length is in contact 

 with the cytoplasm of some cell. 



FIG. 65. Portion of tendon 

 from a cow. conn.t.c., con- 

 nective-tissue cells seen from 

 the side and, in one case, from 

 the surface. 



