510 THE SENSORIAL FUNCTIONS. 



skeleton there exists a small perforation in the roof 

 of the mouth, just behind the sockets of the incisor 

 teeth, forming a communication with the under and 

 fore part of the nostrils. This canal is perceptible 

 only in the dried bones ; for, in the living body, it 

 is completely closed by the membrane lining the 

 mouth, which sends a prolongation into it ; but in 

 quadrupeds, this passage is pervious, even during 

 life, and is sometimes of considerable width. Ja- 

 cobson found, on examining this structure with 

 attention, that the canal led to two glandular 

 organs of an oblong shape, and enclosed in carti- 

 laginous tubes: each gland has in its centre a 

 cavity, which communicates above with the general 

 cavity of the nostrils. These organs lie concealed 

 in a hollow groove within the bone, where they 

 are carefully protected from injury: and they 

 receive a great number of nerves and 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 Rodentia, and next in 

 that of the Ruminantia : in the Horse, they are still 

 very large, but the duct is not pervious ; while in 

 carnivorous quadrupeds, they are on a smaller scale. 

 In Monkejjs, 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 at- 

 tributed to these singularly constructed organs must 

 evidently be quite conjectural. The ample supply 

 of nerves which they receive would indicate their 



