158 COGSWELL — ON THE HUMAN TEETH. 



climbing the floes and hummocks of ice, like the walrus, while the 

 beaver use their teeth also for the purpose of cutting down trees 

 and carrying them in their teeth to build their dams. (Beautifully 

 illustrated by Dr. Gilpin at the last Institute meeting.) The teeth 

 of carnivora and granivora, or such animals as live on flesh, and 

 those who subsist on grain or a mixed diet, the organs of mastica- 

 tion assist to make the distinction, not only in their number but in 

 their density and mode of articulation, having special forms for 

 special uses. 



The names also indicate their use as in man : the front teeth 

 from being commonly adapted to effect the first coarse division of 

 the food, have been called cutters or incisors, — the back teeth which 

 complete its comminution, grinders or molars, and the large conical 

 teeth situated behind the incisors, nearer the masseter muscle are 

 called the canine, or holders, tearers, or laniaries, such as we find 

 in the dog and that class of animals : while the two between the 

 laniaries and the first molars are the bicuspids or double cuspids. 

 In the use of the teeth we find a difference between the granivorous 

 and carnivorous animals : while with flesh eating animals or carni- 

 vorous there is only an up and down motion of the jaw, with well 

 developed cuspid teeth, while with granivorous animals a lateral 

 motion, and a deficiency of the cuspid teeth (in many cases) as in 

 the horse, sheep, cow, &c. 



In man the jaws are short and the crowns of the teeth are of 

 egitaZ length ; no vacant spaces in the dental series of either jaw, 

 and the teeth derive their additional fixity by their close and 

 mutual pressure ; and from these facts, and others, finding also the 

 density of the teeth harder than all others, present in this aspect 

 the highest order of human organization. The structure of the 

 teeth vary from the lowest class to the highest, taking the fish (as 

 the sperm whale) they have no true enamel, while the elephant, 

 walrus, narwhal, consists o^ m,odified dentive called ivory. In the 

 hippopotamus it is said the substance is hard enough to strike fire. 

 This is not an uncommon occurrence in excavating the human 

 tooth, as I have often seen the steel instrument coming suddenly in 

 contact with the enamel, cause a spark of fire to fly off like steel 

 and flint coming in contact. Comparative analysis of the enamel of 



