100 THE HUMAN BODY 



lages commence, the hyaline variety being built up by the in- 

 crease of the cell- capsules and their fusion to form the ma- 

 trix. It persists throughout life in the thin cartilaginous 

 plate of a mouse's external ear. Other varieties of cartilage 

 are really mixtures of true cartilage and connective tissues, 

 and will be considered after the latter. 



The Connective Tissues. These complete the skeleton, 

 marked out in its coarser features by the bones and cartilages, 

 and constitute the final group of the supporting tissues. 

 They occur in all forms, from broad membranes and stout 

 cords to the finest threads forming networks around the other 

 ultimate histological elements of various organs. In addition 

 to subsidiary forms, three main varieties of this tissue are 

 readily distinguishable, viz., areolar, white fibrous, and yellow 

 elastic. Each consists of fibres and cells, the fibres being of 

 two kinds, mixed in nearly equal proportions in the areolar 

 variety, while one kind predominates in one and another in 

 the second of the remaining chief forms. 



Areolar Connective Tissue. This exists abundantly be- 

 neath the skin, where it forms a loose layer which permits 

 the skin to be moved, more or less, to and fro over the sub- 

 jacent parts. Areolar tissue consists of innumerable bands 

 and cords interlacing in all directions, and can be greatly dis- 

 tended by blowing air in at any point, from whence it travels 

 widely through the intercommunicating meshes: if dried 

 while distended it is somewhat like raw cotton in appearance 

 but not so white. In dropsy of the legs or feet the cavities 

 of this tissue are distended with lymph, which in health is 

 present only in sufficient quantity to moisten them. From 

 beneath the skin the areolar tissue extends all through the 

 Body between the muscles and around the blood-vessels and 

 nerves; and still finer layers of it enter into these and other 

 organs and -unite their various parts together. It constitutes 

 in fact a soft packing material which fills up the holes and 

 corners of the Body, as for instance around the blood-vessels 

 and between the muscles in Fig. 4. 



Microscopic Structure of Areolar Tissue. When exam- 

 ined with the microscope areolar tissue is seen to consist of 

 nucleated cells imbedded in a ground-substance which is per- 

 meated by fibres. The fibres everywhere form the predomi- 

 nant feature of the tissue (the homogeneous matrix and the 

 cells being inconspicuous) an'd are of two very different kinds. 



