OP THE ORGANS. 85 



their three dimensions; we often also, use comparisons more 

 or less trivial: for most commonly it is rather difficult to de- 

 termine the form by a comparison with geometrical figures. 



In the interior, some organs are hollow, and form reservoirs 

 or canals opening externally; others form cavities closed on all 

 sides; a third, ramified and closed canals, a fourth is full or 

 massive : but they are all areolar, and more or less perme- 

 able. 



Among the organs, there are some which extend them- 

 selves, branching or radiating from the centre to the circum- 

 ference: such are the vessels, nerves, and the bones themselves. 

 None i.s insulated, all are interlaced and communicate with 

 each other. Finally, there is a great analogy between the 

 organs, as well as the regions. Some of them being exactly 

 similar, by their union, constitute genera. 



83. The colours of the organs are white, red and brown; 

 some of them are transparent, others opaque. Their consis- 

 tence varies from great softness, to an extreme hardness. 

 They are extensible and retractile, flexible, compressible and 

 elastic, but in very different degrees. The cohesion of some 

 is but slight, while others are endowed with such tenacity as 

 to require very great efforts to break them. These properties 

 of colour and cohesion depend much on the liquids which 

 they in a great measure contain. Thus opaque parts, such as 

 the ligamentous tissue, become transparent by dessication ; 

 this same substance, very tenacious and but little elastic when 

 humid, becomes greatly so when dried ; elastic parts, such as 

 the tissue of the arteries become brittle by dessication, &c. 



84. The organs differ, also, greatly with regard to their 

 texture. At the first glance, we see that several of them are 

 formed by the reunion of bundles of parallel or interwoven 

 threads we then say their texture is fibrous. Others are 

 formed by the union of layers or laminae more or less numer- 

 ous and distinct, and usually, closely united. In others again 

 we find granulations or approximated grains closely united 

 with each other. Some of them have apparently a very com- 

 pact, uniform or homogeneous texture, but it is in appearance 



