THE STRUCTUEE OF THE ELEMENTARY TISSUES. 43 



Their great tendency to branch and to form networks by anastomosis. 

 (4.) Their twisted corkscrew-like appearance, and that their free ends 

 usually curl up. (5.) Their yellowish tint and considerable elasticity. 

 (6.) Their resistance to hsematoxylin and similar reagents, and their 

 affinity for magenta and other aniline staining colors. 



These fibres yield on boiling not gelatin, but a gelatinous substance 

 called elastin. 



The chief varieties of connective tissues may be thus classified : 



I. The Fibrous Connective Tissues. 



A. Chief Forms. 



a. White fibrous. 



b. Elastic. 



c. Areolar. 



B. Special Varieties. 



a. Gelatinous. 



b. Adenoid or Retiform. 



c. Adipose. 



II. Cartilage. 



III. Bone and dentine. 



I. FIBROUS CONNECTIVE TISSUES. 



A. Chief Forms. (a.) White Fibrous Tissue. 



Distribution. It is found typically in tendon; also in ligaments, in 

 the periosteum and perichondrium, the dura mater, the pericardium, 

 the sclerotic coat of the eye, the fibrous sheath of the testicle; in the 

 fasciae and aponeuroses of muscles, and in the sheaths of lymphatic 

 glands. 



Structure. To the naked eye tendons and many of the fibrous 

 membranes, when in a fresh state, present an appearance as of watered 

 silk. This is due to the arrangement of the fibres in wavy parallel bun- 

 dles. Under the microscope the tissue appears to consist of long, often 

 parallel, bundles of fibres of different sizes. The fibres of the same bun- 

 dle now and then intersect each other. The cells in tendons (fig. 42) 

 are arranged in long chains in the ground substance separating the bun- 

 dles of fibres, and are more or less regularly quadrilateral with large 

 round nuclei containing nucleoli, which are generally placed so as to be 

 contiguous in two cells. Each of these cells consist of a thick body, 

 from which processes pass in various directions into, and partially fill 

 up the spaces between, the bundles of fibres. The rows of cells are 

 separated from one another by lines of cement substance. The cell 

 spaces can be brought into view by silver nitrate. The cells are gener- 



