TEETH OF MONOPHYODONTS. 281 



The outward and visible dentition of the great Sperm-whale 

 or Cachalot (Physeter macrocephalus) is confined to the lower 

 jaw. The series consists in each ramus of about twenty-seven 

 teeth. In the young they are conical and pointed ; usage renders 

 them obtuse, whilst progressive growth expands and elongates 

 the base into a fang, which then contracts, and is finally solidified 

 and terminated obtusely. The teeth are separated by intervals 

 as broad as themselves. The mode of implantation is inter- 

 mediate between that of the teeth of the Ichthyosaurus, and of 

 those of Delphinus. They are lodged in a wide and moderately 

 deep groove, imperfectly divided into sockets, the septa of which 

 reach only about half-way from the bottom of the groove. These 

 sockets are both too wide and too shallow to retain the teeth in- 

 dependently of the soft parts, so that it commonly happens, when 

 the dense semi-ligamentous gum dries upon the bone, and is 

 stripped off in that state, that it brings away with it the whole 

 series of the teeth like a row of wedges half-driven through a 

 strip of board. A firmer implantation would seem unnecessary 

 for teeth which have no opponents to strike against, but which 

 enter depressions in the opposite gum when the mouth is closed. 

 That gum, however, conceals a few persistent specimens of the 

 primitive foetal series of teeth ; these are always much smaller 

 and more curved than the functional teeth of the lower jaw, of 

 which a section is given in fig. 239, vol. i. p. 362. In the small 

 snub-nosed Cachalot (Physeter simus) the first tooth of this series 

 is exposed in the front of the upper jaw. 1 



The first-formed extremity of the tooth in the young Cachalot 

 is tipped with enamel : when the summit of the crown has been 

 abraded, the tooth consists of a hollow cone of dentine, ib. d, 

 coated by cement, c, and more or less filled up by the ossified 

 pulp, o. Irregular masses of this fourth substance have been 

 found loose in the pulp-cavity of large teeth. The external 

 cement is thickest at the junction of the crown and base, which 

 are not divided by a neck. 



The permanent or mature dentition of the Beluga (Delphinus 

 leucas, Pall.), though scanty, is more normal than in the Physeter, 

 nine functional teeth being retained on each side of the upper 

 jaw, and eight in each ramus of the lower jaw. They present 

 the form of straight subcom pressed obtuse cones. 



The most formidable dentition is that of the predaceous 

 Grampus (Phoccena orca), whose laniariform teeth are as large in 

 proportion to the length of the jaws as in the crocodile ; they are 



1 xcix'. p. 42, pi. 12. 



