42 Proceedings of the Boyal Physical Society. 



the rudimentary teeth and of the palatal mucous membrane 

 are preserved in the University Museum. 



It is known that in Hyperooclon rostratiis teeth have not 

 generally been recognised as protruding through the gum into 

 the cavity of the mouth of the living animal, so that it appears 

 to be edentulous. When the gum is removed, however, from 

 the anterior end of the lower jaw, two well-known distinct 

 teeth are exposed lodged in the mandible near its tip, from 

 the presence of which the specific name hiclens has sometimes 

 been applied to this animal. Occasionally, however, a second 

 mandibular tooth, also concealed by the gum, has been re- 

 cognised close behind the first. Chemnitz found a second 

 smaller tooth on one side of the jaw of his specimen, but not 

 on the other.^ Schlegel said^ that the skeleton in the Leyden 

 Museum had two teeth on the rio-ht side of the mandible 

 upwards of an inch apart, and only one on the left side. Mr 

 Wm. Thompson figured ^ two mandibular teeth about an inch 

 asunder on each side of the jaw of the Belfast skeleton. 

 The most complete account of the dentition of Hyperoodon 

 has, however, been given by Eschricht,* who, in his admirable 

 memoir on this animal, described, in a specimen which he 

 dissected, not only the two well-known mandibular teeth, 

 but a series of small denticles in each side of each jaw. 

 These denticles corresponded in shape and general arrange- 

 ment to what I saw in the Dunbar animal, but they were 

 more numerous, and a greater number had pierced the gum, 

 though many were still imbedded in it. Thirteen were 

 present on the right side of the upper jaw, and probably the 

 same number on the left side. On the right side of the 

 lower jaw, eleven rudimentary teeth had been present ; on 

 the left side they had fallen out. In Eschricht's specimen 

 the rudimentary dentition was a little more advanced than in 

 the animal from Dunbar. Notwithstanding the projection of 

 two of these denticles into the cavity of the mouth in my 



1 Quoted by Wesmael in Nouv. Mem. de I'Acad. Koy. de Bruxelles, 1841, 

 t. xiii. 



2 Abliandlungen, Leiden, 1841, 1 Heft, p. 29. 



3 Annals, op. ciL, vol. xvii., PI. iv., 1846. 

 ^ Die Nordischen Wallthiere, p. 36. 



