THE CONNECTIVE TISSUES. 



the fibres. In the mammals they are placed upon the periphery 

 of the fibres (Fig. 12, ), in the lower vertebrates near the cen- 

 tre. The muscles of the heart agree in origin and cross-band- 

 ing with the voluntary muscles, but differ in being cellular rather 

 than syncytial, and in being removed from the control of the 

 will. All cross-banded muscles are capable of rapid contrac- 

 tions. 



The connective tissues are all of mesenchymatous origin, and 

 are characterized by a great development of the intercellular 

 substance, which 

 is usually a pro- 

 duct of the cells. 

 They are the sup- 

 porting tissues of 

 the body, and 

 vary accordingly 

 as this intercellu- 

 lar substance va- 

 ries, and may 

 correspondingly 

 be grouped under 

 several subheads, -. 



rlG. 13. fibrous non-elastic connective tissue 



the principal ones (f rom Martin). 



being enumerated below. 



In fibrous connective tissue (white or non-elastic tissue) the 



cells are branched or spindle-shaped, and the intercellular sub- 

 stance is more or less fibrous, 

 the fibres being parallel, in- 

 terlaced, or in a network, so 

 that there result sheets, mem- 

 branes, or bundles, accord- 

 ingly as the part to be played 

 varies. In some cases this tis- 

 sue is loose (areolar tissue), 

 such as is found between the 



FIG. 14. Fat. ,, oil globules in the gkm &nd de t at 



connective tissue cells. . . 



other times it is much firmer, 

 as in the case of tendons. This type of tissue also gives rise to 



