PERCEPTIONS OF ANIMALS. 5()9 



blood-vessels, resembling in this respect the 

 organs of the senses. Their structure is the 

 same in all quadrupeds in which they have been 

 examined ; but they are largest in the family of 

 the Rodent ia, and next in that of the Ruminantia: 

 in the Horse, they are still very large, but the 

 duct is not pervious ; while in carnivorous quad- 

 rupeds, they are on a smaller scale. In Mon- 

 keys, they may still be traced, although ex- 

 tremely small ; appearing to form a link in the 

 chain of gradation connecting this tribe with the 

 human race, in whom every vestige of these 

 organs has disappeared, excepting the aperture 

 in the bones already noticed. Any use that can 

 be attributed to these singularly constructed 

 organs must evidently be quite conjectural. The 

 ample supply of nerves which they receive 

 would indicate their performing some sensitive 

 function ; and their situation would point them 

 out as fitting them for the appreciation of objects 

 presented to the mouth to be used as food : 

 hence it is probable that the perceptions they 

 convey have a close affinity with those of smell 

 and taste. 



The larger cartilaginous fishes, as Sharks and 

 Rays, have been supposed by Treviranus to be 

 endowed with a peculiar sense, from their having 

 an organ of a tubular structure on the top of the 

 head, and immediately under the skin. Roux 

 considers it as conveying sensations intermediate 



