n] 



HISTOLOGY 



1!) 



pact bone the blood vessels are contained in little canals — the 

 Haversian canals — which are very numerous tlu'oughout the 

 bone ; in cancellated bone the vessels run in the interstices into 

 which the bone marrow extends. The marrow is contamed 

 chiefly in the hollow cavit}- which extends throughout the length 

 of the shaft but is not continued into the enlarged ends. The 

 marrow consists largely of fat, but often contains a consider- 

 able amount of blood, which then gives it a characteristic red 

 colour. 



Reticular tissue also occurs in bone marrow, as well as in the 

 liver, spleen, IjTnphatic glands, and various other parts of the 

 body. It is essentially a connective tissue in which the inter- 

 cellular substance has partly disappeared or been replaced by 

 fluid, but it contains white fibres, and sometimes elastic fibres. 



Lymphoid tissue may be described as reticular tissue or areolar 

 tissue in which the meshes are packed with large numbers of 

 small round cells called lymphocytes or lymph corpuscles. It 

 occurs in the spleen, tonsils, and thymus, and in all lymphatic 

 glands. (For figures of spleen and thymus see pages 148-9.) 



Adipose tissue is connective tissue containing a large pro- 

 portion of fat in its cells. The fat globules are at first very small, 



Fig. 13. Adipose tissue (after Gmy). u crystals of fatty acids. 



and then gradually increase in size so as to coalesce, pushing the 

 cell protoplasm with its nucleus to the periphery or chiefly to 

 one side, so that there comes to exist a single fat globule sur- 

 rounded bj' a thin lajer of cell substance a portion of \\hich 



