48 GENERAL ANATOMY. 



of white blood-corpuscles, and like them possessed of amoeboid movements ; others 

 are of larger size, and do not exhibit amoeboid movements to any appreciable 

 extent. They lie imbedded in the ground-substance, and in some situations, 

 where the areolar tissue is loose and the spaces large, so as to contain several cells, 

 they form a sort of lining for it. In other situations where the tissue forms a 

 membranous layer, the flattened cells, here unbranched, form an epithelial-like 

 covering to its surface. 



Vessels and Nerves of Connective Tissue. The blood-vessels of connective tissue 

 are very few that is to say, there are few actually destined for the tissue itself, 

 although many vessels may permeate one of its forms, the areolar tissue, carrying 

 blood to other structures. In white fibrous tissue the blood-vessels usually run 

 parallel to the longitudinal bundles and between them, sending transverse com- 

 municating branches across, and in some forms, as the periosteum and dura mater, 

 being fairly numerous. In the yellow elastic tissue the blood-vessels also run 

 between the fibres, and do not penetrate them. Lymphatic vessels are very numer- 

 ous in most forms of connective tissue, especially in the areolar tissue beneath the 

 skin and the mucous and the serous surfaces. They are also found in abundance 

 in the sheaths of tendons, as well as in the tendons themselves. Nerves are to 

 be found in the white fibrous tissue, where they terminate in a special manner ; 

 but it is doubtful whether any nerves terminate in areolar tissue ; at all events, 

 they have not yet been demonstrated, and the tissue is possessed of very little 

 sensibility. 



Development of Connective Tissue. Fibrous connective tissue is developed from 

 embryonic connective-tissue cells derived from the mesoblast. At an early period 

 of development it consists of nucleated cells and a muco-albuminous fluid, which 

 subsequently becomes a pellucid jelly and forms the ground-substance. In this 

 ground-substance the two varieties of fibres become developed. As to the manner 

 in which they do so there are two theories, some believing that they are developed 

 from the protoplasm of the cells, others that they are formed by a deposit in the 

 ground-substance. In the former case the protoplasm of the cells is converted 

 wholly into elementary fibres, the nucleus disappearing; or else the peripheral 

 part of the protoplasm produces the fibrous tissue, the original cell growing again 

 to its original size, and then throwing off a fresh portion to form a new cell, and 

 itself persisting in contact with the fibres it has formed as a permanent connective- 

 tissue corpuscle. 



Three special forms of connective tissue must be described : the mucoid, the 

 lymphoid or retiform, and basement-membranes. 



1. The mucoid or gelatinous connective tissue exists chiefly in the "jelly of 

 Wharton," which forms the bulk of the umbilical cord, but is also found in some 

 other situations in the foetus, as in the pulp of young teeth, and in certain stages 

 of the development of connective tissue in various regions. In the adult the vit- 

 reous humor of the eye is formed of the same material. This tissue consists of 

 nucleated cells, which branch and become connected so as to form trabeculse, 

 which traverse a jelly-like ground substance, containing the chemical principle of 

 mucus, or mucin, and in smaller quantities albumen, but no gelatin. Sometimes, 

 as in the vitreous humor of the eye, the cells almost completely disappear and the 

 jelly only remains. 



2. Retiform connective tissue (Fig. 18) is found extensively in many parts of 

 the body, forming the framework of some organs and entering into the construc- 

 tion of many mucous membranes. It is formed of an interlacement or network of 

 very fine fibres, which closely resemble white fibrous tissue, and in certain situ- 

 ations may be demonstrated to be continuous with it. In their behavior to certain 

 reagents, however, they differ from the ordinary Avhite fibres, and have conse- 

 quently been held to be a third form of connective-tissue fibres. In many places 

 flattened cells may be seen connected with the fibres and partially concealing them, 

 presenting an appearance as if the tissue were formed of a network of branching 

 and anastomosing cells. This, however, is not so, as the cells can be removed or 



