CLASSIFICATION OF THE TISSUES. 233 



theliurn. The nails and the hair are classed with epithelium also: 

 though the latter is often classed with teeth, and is, at the same 

 time, a compound tissue. 



Only the highest form of muscular tissue (the striated) is strictly 

 compound; but there is an obvious advantage in arranging and 

 describing the two forms in connection. 



The fat-ce/fc are a simple tissue ; but adipose tissue is not so, and 

 hence it is placed in the second class. It would be in accordance 

 with analogy to term the fat-cells alone fatty tissue, and, when con- 

 nected together with their vessels by areolar tissue, to apply the 

 term fat as we speak ' of osseous tissue and bone, of muscular 

 tissue and muscle. In that case the term adipose tissue might be 

 dropped, or adipose tissue and adipose might be used. For the pre- 

 sent, however, it appears necessary to retain, as correlative terms, 

 fat-cells and adipose tissue. 



It will be hereafter seen that the mucous and serous membranes, 

 and the skin, are composed of the same histological elements; and 

 they are, therefore, here classed together. The vessels and the 

 heart present no peculiar histological elements ; but they are sepa- 

 rately described on account of their great physiological importance. 

 For a similar reason, distinct chapters are devoted to the alimentary 

 canal, the urinary, the sexual, and the respiratory apparatus, the 

 ductless glands, and the sensory organs. 



Classification of the Tissues. 



FIRST CLASS. SIMPLE TISSUES. 



1. Epithelium. Hair and Nails. 



2. Yellow Fibrous (Elastic) Tissue. 



3. White Fibrous (Collagenous) Tissue. 



4. Osseous Tissue, including Teeth. 



SECOND CLASS. COMPOUND TISSUES. 



1. Areolar Tissue. 



2. Adipose Tissue. 



3. Cartilage and Fibro-Cartilage. 



4. Contractile or Muscular Tissue (two forms). 



5. Nervous Tissue Vesicular and Fibrous. 



{Cutaneous (Skin.) 

 Mucous. 

 Serous. 



7. The Vessels. 



8. Alimentary Canal and Appendages. 



9. Urinary Apparatus. 



