CONNECTIVE TISSUE 



resembling those of reticular tissue appear in the ectoplasm (Fig. 291 A); 

 (2) the anastomosing fibers take the form of parallel bundles and are 

 converted, through a chemical change, into typical white fibers. The 

 spindle-shaped cells are transformed into the connective-tissue cells 

 characteristic of the adult. In areolar tissue, the bundles of white fibers 

 are interwoven to form a mesh work; in tendon they are arranged incompact, 

 parallel fascicles. The cells of the tendons are compressed between the 

 bundles of fibers and this accounts for their peculiar form and arrangement. 



Mesenehymal cell 



Fibril/a in ectoplasmic 

 matrix 



Cell of syncyttum 

 Elastic fiber 



I Mesenehymal cell 



Cartilage matrit 



Cartilage cell 



PIG. 291. The differentiation of the supporting tissues (after Mall). X 270. A, White 

 fibers in the corium of a 5 cm. pig embryo; B, elastic fibers in the umbilical cord of a 7 cm. pig 

 embryo; C, cartilage from the occipital bone of a 20 mm. pig embryo. 



In the cornea of the eye, the cells retain their processes. The corneal 

 tissue is thus embryonic in character and is without elastic fibers or blood 

 vessels. 



Elastic Tissue. With the exception of the cornea and tendon, 

 yellow elastic fibers develop in connection with all white fibrous connective 

 tissue. Like the white fibers, they are produced in the ectoplasm of the 

 mesenchymal syncytium (Fig. 291 B). They are developed as single 

 fibers, but may coalesce to form the fenestrated membranes of the arteries. 

 According to Ranvier, elastic fibers are produced by the union of ecto- 

 plasmic granules, but this view is not supported by either Mall or Spalte- 

 holz. 



