24 



Anatomy of the Rabbit. 



h-ep. 



There is a close association between the epithelia of the surface 

 of the body and the nervous tissues, arising from the circumstance 

 that they are derivatives of a common embryonic layer, the ecto- 

 derm. In the adult we may distinguish as sensory epithelia 

 special aggregations of cells lying either in a deep or superficial 

 position, and associated more or less closely with the central 

 nervous system. They comprise the olfactory epithelium of the 

 nasal cavity, some of the cells of which are true nerve cells, the 

 gustatory epithelium of the tongue, and the auditory epithelium 



of the membranous labyrinth 

 of the ear. The retina — the 

 nervous portion of the eye — is a 

 modified, portion of the central 

 nervous system. 



As linings of surfaces, the 

 ordinary, epithelia may be dis- 

 tinguished from certain special 

 coverings of internal spaces, the 

 endothelia and mesothelia. The 

 latter consist microscopically of 

 thin pavement-like cells. They 

 differ from epithelia in origin, being 

 formed, not in connection with 

 originally free surfaces, but in 

 relation to spaces of the mesoderm 

 or intermediate layer of the body. 

 Endothelia form the linings of 

 blood vessels and lymph canals, 

 while mesothelia are the chief 

 layers of the smooth, moist serous membranes which line the 

 peritoneal, pleural, and pericardial cavities. 



2. Connective Tissues. 

 The connective tissues form the supporting elements of the 

 body. As ordinary connective tissues they serve to connect 

 organs or parts of organs together, and as skeletal tissues they 

 provide the rigid framework or skeleton from which all soft parts 

 of the body are suspended. They are distinguished by the presence 

 of two main components — the cell basis, and the intercellular 



1-f.s 



J — m.c.m. 



Fig. s. From a section of the skin 

 of the side of the body of an adult rabbit. 

 X about lo; showing the grouping of the 

 hair-follicles: co., corium; ep., epithelium; 

 m.c.m,, cutaneus maximus muscle; t.s., 

 subcutaneous tissue. 



