70 Mr. Owen on the Zeuglodon cetoides. 



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. They are compressed and 

 conical, with an ohtuse apex: the longitudinal diameter of the middle one (6.) is 

 three inches, the transverse diameter of the same is one inch two lines ; the height 

 ahove the alveolar process two inches and a half. The crown is contracted in the 

 middle, so as to give its transverse section somewhat of the hour-glass form* (PI. 

 VIII. fig. I); and the opposite wide longitudinal grooves, which produce this form, 

 hecome deeper as the crown approaches the socket, and at length meet, and 

 divide the root of the tooth into two separate fangs : this fact, which was not 

 clearly demonstrated in the original fossil, is proved by the transverse sections 

 helow the crown of one of the teeth (PL VIII. fig. 2). The anterior tooth (PI. 

 VI [. a.) is somewhat smaller than the posterior ones, and presents also a more 

 simple structure. The vertical groove is deeper in the two posterior teeth, and, 

 in the hindmost (c), which is much broken, it gives the appearance of two distinct 

 simple teeth. Besides the teeth implanted in the jaws as above described, there 

 is a fragment of a tooth imbedded in the matrix containing the above pieces, and 

 consisting of the base of the crown and beginning of the fangs. The crown of 

 this tooth, which is equal in size to the posterior one in place, and was probably 

 a tooth of the same jaw, is partly worn down and partly broken, but is so blend- 

 ed with the matrix, that its exact form could not be determined. Of this tooth 

 I had a transverse section made near to the base of the crown, which presents the 

 figure represented in PI. VIII. fig. 1, and is that form which we may reasonably 

 suppose would be characteristic of the old and worn-down teeth of the Zeuglodon. 

 The crown is divided into two irregular rounded portions or lobes, placed one 

 before the other, and joined by a narrow neck or isthmus. The anterior lobe is 

 the broadest, its grinding surface is subovate, and placed obliquely ; it measures 

 one inch, three lines in the long diameter, one inch in the short diameter ; the 

 posterior lobe is narrower, more regularly ovate with the long diameter (which is 

 one inch, three lines), placed parallel with the axis of the jaw. The isthmus is 

 about three lines in breadth and two in length ; but the breadth diminishes while 

 the length increases as the tooth descends in the socket, until it finally disappears, 

 and the two portions take on the character of separate fangs. It is evident that 

 the pulp which, from the form and structure of the crown, was originally simple, 

 has soon become divided into two parts, and that its calcification has proceeded 

 towards two distinct centres, which are each separately surrounded by concentric 

 striae of growth, the exterior of which sends an acute-angled process into the isth- 

 mus uniting the two portions. The cavitas pulpi, which is very small in the crown 



* The term Zeuglodoti (ZevyXi;, a yoke, ocovs, a tooth,) which I have substituted for that oi Basilo' 

 saurus, is expressive of this form of the teeth, wliich resembles two simple teeth linked or yoked together. 



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