36 HANDBOOK OF PHYSIOLOGY. 



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. 

 38). 



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

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

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

 solutions. The lymphoid corpuscles found in the interstices of the tis- 

 sue are small round cells, the protoplasm of which is practically occupied 

 by their spherical nuclei. 



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



Fio. 39. Portion of submucous tissue of gravid uterus of sow. a, branched cells, more or less 

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



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. 



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 " rnesoblast. v 



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

 of fusiform cells (Fig. 39). 



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

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

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

 either by part of the cells becoming fibrils, the others remaining as con- 

 nective-tissue corpuscles, or by the fibrils being developed from the out- 

 side layers of the protoplasm of the cells, which grow up again to their 

 original size and remain imbedded among the fibres. The process gives 

 rise to fibres arranged in the one case in interlacing networks (areo- 

 lar tissue), in the other in parallel bundles (white fibrous tissue). In 

 the mature forms of purely fibrous tissue not only the remnants of the 



