CHAPTER XI 

 HORNY TEETH 



THE teeth of the Cyclostomata (Lampreys, &c.) are horny 

 cones ; they show no true calcification, but are made up of 

 cornified cells of the stratum corneum of the epidermis. 

 New horny cones are formed beneath the tooth in use, and 

 successively take its place when shed. 



In the Lamprey (Petromyzori) these horny structures are 

 found at the sides of the mouth and on the tip of the tongue. 



In the Hagfish (Bdellostoma) there is a single tooth in 

 the roof of the mouth and minute teeth upon the tongue. 

 This fish is partly parasitic in its habits, living on the mud 

 at the sea bottom, and often boring its way into the bodies 

 of large fish, especially the cod, to which it is often very 

 destructive, eating out the soft parts of its prey by means 

 of the rasping action of its tongue teeth. 



Beard (2) has described in Bdellostoma the existence of 

 a true layer of odontoblasts and the formation of a cap of 

 imperfectly calcified dentine, and he considered that his pre- 

 parations showed a small cap of enamel upon this dentine. 

 Warren (8), however, denies the presence of calcified 

 enamel or dentine, and shows that a differential stain (picro- 

 nigrosin) indicates that there is no calcification, but the 

 tooth is entirely horny. There is simply a superficial 

 resemblance to calcified teeth, and no odontoblasts are 

 formed. He considers that the dentine cap described by 

 Beard is the succeeding horny tooth beneath that in use, 

 and that it arises in the same manner by the cornification 

 of epithelial cells. Professor Howes (4) in 1894 expressed 

 the opinion that the ' odontoblasts ' which Beard described 

 showed no calcification, and Ayres (1) in the same year 

 could find no trace of dentine or enamel 



If Warren's views are accepted, and the evidence afforded 

 by his specimens would appear to be conclusive, these teeth 



