16 



PHYSIOLOGY OF FARM ANIMALS 



[CH. 



admitting of the necessary amount of elasticity or rigidity. In 

 embryonic development they have an identical origin, and there 

 are all gradations between the various kinds of connective tissue. 

 They agree further in having a large amount of intercellular 

 cementmg substance, and in this substance fibres are developed. 

 Although situated outside of the cells this intercellular substance 

 in the first instance was derived from the cells. 



One of the commonest kinds of connective tissue is called 

 areolar tissue, which is found in great abundance just under the 

 skin. It consists largely of a close meshwork formed of bundles 

 of fibres which^are white in colour and very fine and wavy. 



Fig. 8. Areolar tissue (after Szymonovicz from Halli- 

 burton). 1 branched cell, 2 white blood corpuscle emi- 

 grated from a neighbouring vessel, 3 elastic fibres, 

 4 white fibres. 



Elastic fibres are also present. These are generally thicker than 

 the white fibres; they are yellowish in colour, and as a rule 

 much straighter. In addition to the fibres there is a clear ground 

 substance containing several kinds of cells which can be seen 

 lying amid the fibres. The cells, which contain easily discernible 

 nuclei, are in many cases flattened and branched, but there are 

 other kinds of cells which resemble or are identical with some of 

 the white corpiiscles of the blood. 



Fibrous tissue which we find in tendon or sinew is almost 

 wholly composed of white fibres. In elastic tissue which occurs 

 in ligaments as well as in the lungs and the walls of the blood 

 vessels elastic fibres are the chief constituent. Otherwise both 

 these kinds of connective tissue resemble areolar tissue. 



Cartilage, commonly called gristle, is a modified form of fibrous 



