20 



DESCRIPTION OF THE PLATES. 



pulp- cavity indicated by a dotted line. 

 Fig. 2. Tooth of the Gavialis gangeticus : 

 a, base absorbed and penetrated by, b, 

 a successional tooth ; c, germ of a third 

 tooth. Fig. 3. Back part of the series of 

 teeth of the lower jaw of the Alligator 

 niger, with the inner wall of the alveolar 

 groove removed showing the absence of 

 partitions, and the germs of the succes- 

 sional teeth. Fig. 4. Middle part of the 

 series of teeth of the same species, exposed 

 by removal of the outer alveolar wall, 

 showing the partitions forming here dis- 

 tinct sockets, from which the teeth are 

 raised to show the germs of successional 

 teeth, and the dentiparous cavities, a, a 

 tooth turned round to show the effect of 

 the new germ upon its base ; b, the shell 

 of an old tooth and two successors. Fig. 5. 

 The root of an old tooth of the Black 

 Alligator, penetrated by its successor. 

 Fig. 6. Base of the same. Fig. 7. Op- 

 posite end from which the crown has 

 been broken away, showing the apex of 

 that of the new tooth. Original. 



PLATE 75 A. 



Fig. 1.— Skull of an Alligator. Fig. 2. 

 Skull of a Crocodile. Fig. 3. Skull 

 of a Gavial. Fig. 4. Skull of a Te- 

 leosaur. Fig. 5. a, b, two views of a 

 tooth of the Marmorosaurus obtusus : c, 

 interrupted ridges of enamel on the base 

 of the crown, magnified. Fig. 6. a, side 

 view ; b, edge view of the tooth of Hylceo- 

 saumsQ). Fig. 7. a, side view; b, edge 

 view of the tooth of Cardiodon rugulosus : c, 

 edge view of a larger tooth of the same 

 species ; d, surface of the enamel, magni- 

 fied. 



PLATE 76. 



Fig. 1. — Side view of the jaws of the Orni- 

 ihorhynchus paradoxus, showing the posi- 



tion of a the incisive and b the molar 

 horny teeth. F. Cuvier. Fig. 2. Left 

 ramus of the lower jaw, showing the 

 working or free surface of a the incisive, 

 b the molar tooth. F. Cuvier. Fig. 3. 

 A diminished view of a transverse slice of 

 a small portion of the molar tooth of the 

 Ornithorhynchus, showing the concentric 

 walls of the canals of the principal tubes, 

 and the minute pores or cells of the den- 

 ser cementing fibrous substance. Fig. 4. 

 View of the open mouth of a very young 

 Fin- whale, (Baloenoptera) . Brandt and 

 Ratzeburg. a. The outer vertical mar- 

 gins of the baleen plates ; the letter is 

 placed just above the horizontal line, or 

 ' bead' of Hunter, which indicates the 

 extent to which the cementing substance 

 descends [in the interspaces of the plates. 

 b. The inner oblique bristled margins of 

 the baleen-plates, c. The large tongue. 

 Fig. 5. A vertical section of four baleen 

 plates in situ. The transverse bar below 

 the numeral represents the vascular gum 

 from which the pulps proceed that pene- 

 trate the base of the plates. Below this 

 is shown the elastic substance cementing 

 the plates together ; beyond which the 

 plates project free, and terminate in the 

 fringe of bristles at c. Hunter. Fig. 6. 

 A diagram of the matrix of the baleen- 

 plate, a. Dotted outline of the pulp, 

 which forms b, the central fibrous part of 

 the plate ; c, the external layers of firm 

 substance formed by the elastic cementing 

 material. Fig. 7. A transverse slice of a 

 portion of a baleen-plate, shewing the 

 arese of the tubular cavities of the coarse 

 central fibres, and the outer denser sub- 

 stance. Heusinger.* Fig. 8. Side view of 

 the upper and lower molars of the Oryc- 

 teropus Capensis. F. Cuvier. Fig. 9. 



* System der Histo/ogie, 4to. 1822. 



