THIRD DIVISION. 





 THE TISSUES. 



CLASSIFICATION OF THE TISSUES. 



No classification of the tissues is possible which is not liable to 

 some objections ; but the following is proposed as the most simple, 

 for the use of the student in histology. All tissues in which the 

 microscope detects but one of the simple histological elements 

 whether cells, fibres, or membrane are termed simple tissues; while 

 if two or more elements are seen as cells and fibres, or cells, fibres, 

 and homogeneous substance such are termed compound tissues. 

 And the latter are termed binary or ternary, if constituted respect- 

 ively of two or three elements. 



In any classification, the distinction between mere tissues, and 

 organs consisting in great part of those tissues, must be kept in 

 mind. E. g. white fibrous tissue constitutes a great part of the 

 ligaments and tendons ; but mere white fibrous tissue is one thing, 

 while a tendon or a ligament is another the latter containing 

 bloodvessels and areolar tissue, together with much of the tissue in 

 question. So bone-tissue, or osseous tissue, is a simple tissue; but 

 a bone is a compound organ, consisting of osseous tissue, vessels, 

 nerves, lymphatics, &c. 



We must also distinguish, in a classification, the tissue itself, 

 from mere cavities which are found in it. Even though the latter 

 may be peculiar to the tissue, and characteristic, they constitute no 

 part of it whatever, and must exert no influence in deciding to 

 what class the tissue belongs. These remarks apply more espe- 

 cially to osseous tissue, this being a simple tissue; though the 

 cavities (lacunae and pores) are more characteristic of bone, as seen 

 under the microscope, than is even the solid substance itself. 



Dental tissue is here associated with the osseous, though the 

 enamel is more nearly allied, in its method of development, to epi- 



