34 HAND-BOOK OF PHYSIOLOGY. 



Structure. It consists of cells, which in the vitreous humor are 

 rounded, and in the jelly of the enamel organ are stellate, imbedded in a 

 soft jelly-like intercellular substance which forms the bulk of the tissue, 

 and which contains a considerable quantity of mucin. In the umbilical 

 cord, that part of the jelly immediately surrounding the stellate cells 

 shows marks of obscure fibrillation. 



(b.) Adenoid or Retiform. 



Distribution. It composes the stroma of the spleen and lymphatic 

 glands, and is found also in the thymus, in the tonsils, in the follicular 

 glands of the tongue, in Peyer's patches and in the solitary glands of the 

 intestines, and in the mucous membranes generally. 



Structure. Adenoid or retiform tissue consists of a very delicate net- 

 work of minute fibrils, formed originally by the union of processes of 

 branched connective-tissue corpuscles the nuclei of which, however, are 

 visible only during the early periods of development of the tissue 

 (Fig. 32). 



The nuclei found on the fibrillar meshwork do not form an essential 

 part of it. The fibrils are neither white fibrous nor elastic tissue, as they 

 are insoluble in boiling water, although readily soluble in hot alkaline 

 solutions. 



(c.) Neuroglia. This tissue forms the support of the Nervous ele- 

 ments in the Brain and Spinal cord. It consists of a very fine meshwork 

 of fibrils, said to be elastic, and with nucleated plates which constitute 

 the connective-tissue corpuscles imbedded in it. 



Fio. 33. Portion of the submucous tissue of gravid uterus of sow. a, branched cells, more or less 

 spindle-shaped; 6. bundles of connective tissue. (Klein.) 



Development of Fibrous Tissues. In the embryo the place of 

 the fibrous tissues is at first occupied by a mass of roundish cells, derived 

 from the "mesoblast." 



These develop either into a network of branched cells, or into groups 

 of fusiform cells (Fig. 33). 



The cells are imbedded in a semi-fluid albuminous substance derived 

 either from the cells themselves or from the neighboring blood-vessels; 

 this afterward forms the cement substance. In it fibres are developed, 



