212 FOSSIL JAWS FROM STONESFIELD. 



mentum of the human teeth, and those of other animals ; but the ccementum 

 of the dugong differs from that of the pachyderms and ruminants in being 

 traversed by numerous caleigerous tubes, the corpuscles or cells being scat- 

 tered in the interstices of these tubes. Now the crowns of the teeth of the 

 Basilosaurus evidently exhibit in many parts a thin investing layer of a 

 substance distinct from the body or ivory of the tooth, and the microscopic 

 examination of a thin layer of this substance proves it to possess the same 

 characters as the ccementum of the crown of the tooth of the dugong. The 

 purkingian cells are, in some places, scattered irregularly, but in others are 

 arranged in parallel rows. The tubes radiating from the cells are wider 

 than usual at the commencement ; but soon divide and sub-divide, forming 

 rich reticulations in the interspaces, and communicating with the branches 

 of the parallel larger tubes. These are placed, as in the dugong, perpen- 

 dicular to the surface of the tooth, but they are less regularly arranged than 

 the caleigerous tubes of the ivory, with which, however, they form numerous 

 continuations. There is a greater proportion of ccementum in the isthmus 

 of the tooth than elsewhere ; and the worn-down crown of the tooth must 

 therefore have exhibited a complicated structure. The entire substance of 

 the ivory of the teeth consists of fine caleigerous tubes radiating from the 

 centres of the two lobes, without any intermixture of coarser medullary 

 tubes which characterize the teeth of the Iguanodon ; or the slightest trace 

 of the reticulated canal, which distinguish the texture of the teeth of the 

 Sphyrcena and its congeners. The caleigerous tubes undulate regularly, 

 and like those of the dugong, exhibit more plainly the primary dichotomous 

 bifurcations, and the subordinate lateral branches given off at acute angles : 

 they also communicate with numerous minute cells arranged in concentric 

 lines. 



" Thus, the microscopic characters of the texture of the teeth of the great 

 Basilosaurus are strictly of a mammiferous nature ; and Mr. Owen further 

 showed that they differ from those of the fossil Edentata, which are also 

 surrounded by ccementum, in the absence of the coarse central ivory ; and 

 confirm the inference respecting the position of the fossil in the natural 

 system drawn from the external aspect of the teeth. 



" Mr. Owen then adduced further proofs of the mammiferous and ceta- 

 ceous character of the Basilosau rus from the structure of the vertebrce, which 

 proves that the epiphyseal lamince were originally separated from the body 

 of the vertebrce, but were afterwards united to it. In the bodies of the 

 smaller vertebrce the epiphyses are wanting, and Mr. Owen agrees with Dr. 

 Harlan in inferring from the common occurrence of this condition, that 

 there were originally three separate points of ossification in the body of the 

 vertebrce ; a character never noticed in the vertebrce of saurians, but a most 

 prominent one in those of the Cetacea. Another argument in favour of the 

 mammiferous and cetaceous nature of the Basilosaurus is deduced from the 

 great capacity of the canal for the spinal chord, which in the Cetacea is 

 surrounded by an unusually thick plexiform stratum of both arteries and 

 veins. The cetaceous character is further manifested in the short antero- 

 posterior extent of the neurapophyses as compared with that of the body 

 of the vertebra ; in their regular concave posterior margin, and the deve- 

 lopment of the articular apophyses only from their anterior part : also in 

 the form and position of the transverse processes, which however present a 

 greater vertical thickness than in the true Cetacea, and approach in this 

 respect to the vertebrce of the dugong. 



" With respect to the other bones of the Basilosaurus, Mr. Owen stated 

 that the ribs in their excentric laminated structure are peculiar, and unlike 

 those of any mammal or saurian. The hollow structure of the lower jaw 

 of the Basilosaurus, which has been advanced as a proof of its saurian 



