360 CETACEANS, 



of the teeth of the Platanista, contracts in every direction and gives 

 the tooth the form of " a double cone," as described by Hunter, 

 one point being exserted the other having the reverse direction and 

 inserted. The conversion of the last remnant of the pulp produces 

 the irregular bone-like deposit in the centre of the tooth, and closes 

 up the lower aperture, one or two minute canals for the nutrient 

 vessels being usually left. The mass of this fourth central substance 

 is greatest in the Cachalot, in which the process sometimes com- 

 mences at an independent centre and proceeds centrifugally as in 

 ordinary ossification, giving rise to the detached stalactitic masses 

 occasionally found loose in the unclosed pulp-cavity of large teeth. 



146. Zeuglodon.[\) The remains of a gigantic animal, dis- 

 covered in a tertiary formation in the state of Louisiana, and 

 originally interpreted to belong to the class of Reptiles with the 

 name of Basilosaurus,{'2) presented in portions of both upper and 

 lower jaws, teeth implanted by a double fang in deep sockets. 

 This anatomical peculiarity of a mammiferous species, though its 

 occurrence in the supposed Basilosaurus has been cited in deprecia- 

 tion of the value of the character of the two-fanged tooth in the 

 determination of fossil remains, (3) has had its importance established 

 by the result of a closer examination of the remains of the supposed 

 gigantic Reptile, which has proved their mammalian and cetaceous 

 character. (4) 



The crowns of the teeth in the largest portion of the upper 

 jaw which has hitherto been obtained are more or less perfect, 

 and are contiguous to each other ; but they are placed rather 

 obliquely so that the inner surface of the anterior part of the crown 

 of the hinder tooth is on the same line as the outer surface of 

 the posterior part of the tooth next in front. 



The crowns are sub-compressed and conical, with an obtuse apex : 



(1) ZtvyXr], a yoke, oSova, a tooth, expressive of the peculiarity of certain teeth of this 

 genus resembling two teeth linked or yoked together. 



(2) Dr. Harlan, Medical and Physical Researches, 1835, pp. 337, 369. 



(3) Dr. Grant, in Thomson's British Annual, 1838, p. 265. 



(4) See my Paper on the Zeuglodon, Geological Transactions, Ilnd Series, vol. vi. p. 69. — 

 An almest entire skeleton which has been since brought to light has fully confirmed the 

 deductions therein recorded. 



