DESCRIPTION OF THE PLATES, 



23 



gustidens, |th nat. size, i, i. Outlines of 

 lower and of base of upper incisive tusks; 

 m, 6 and'm, 7, penultimate and last mo- 

 lar teeth. Kaup. 



PLATE 91. 



Fig. 1. — Transverse section of crown of 

 molar of Zeuglodon ceto'ides ; a, isth- 

 mus connecting the two lobes. Fig. 2. 

 Magnified view of portion of transverse 

 section of the same ; a, central osteo- 

 dentin ; b b, unvascular dentine, showing 

 contour lines of basal substance ; c, ce- 

 ment. Fig. 3. Small portion of outer 

 part of previous section more highly- 

 magnified, showing/, indications of den- 

 tinal cells, secondary branches, and e, 

 terminations of dentinal tubes ; d, cellular 

 and fine tubed cement. Original. 



PLATE 92. 



A section of the upper jaw of a young Du- 

 gong, (Halicore indicus) showing all the 

 teeth that are developed in that jaw in 

 situ ; \ nat. size : a, deciduous incisor ; 

 b, permanent incisor, in longitudinal sec- 

 tion ; c, first molar ; d, second molar 

 e, third molar : these three molars are 

 deciduous, but are not replaced by suc- 

 cessors : f, fourth molar ; g, fifth molar. 

 These two molars are persistent and cha- 

 racterize the adult Dugong. Original. 



PLATE 93. 



Fig. 1 . — Base view of upper jaw of Dugong, 

 \ nat. size ; e, remains of third or ante- 

 penultimate molar ; /, penultimate molar ; 

 g, last molar. Fig. 2. Upper view of 

 left ramus of lower jaw, \ nat. size ; a, 

 abortive incisor in one of the sockets of 

 the deflected symphysis : e, antepenulti- 

 mate molar ; f, penultimate molar ; g, 



last molar. Behind this is exposed a 

 cavity in the substance of the jaw ; not 

 an alveolus. Fig. 3. Abortive incisor 

 of the lower jaw, nat. size : a, contracted 

 base, or pulp-cavity ; b, crown wasted by 

 the absorbent process. Fig. 4. Section 

 of incisive tusk of male ; ^-nat. size. Fig. 5. 

 Side view of antepenultimate molar, nat. 

 size. Fig. 6. Crown of last upper molar, 

 nat. size. The clear outer border shows the 

 thickness of the cement. Home. 



PLATE 94. 



Reduced figure of a magnified view of a 

 transverse section of the penultimate 

 molar of a Dugong, showing the thick 

 border of cement ; the cells of the dentine 

 near that border ; the course of the den- 

 tinal tubes, and the central osteo-dentine. 

 * Nat. size. Original. 



PLATE 95. 



Fig. 1 . — Magnified view of a section of the 

 incisive tusk ; c, the cement, with ra- 

 diated cells ; e, the enamel, d, the 

 dentine, showing the course and termina- 

 tions of the tubes, and the peripheral 

 outlines of the dentinal cells. Fig. 2. 

 Magnified view of part of a transverse 

 section of the same tusk : a, transverse 

 sections of tein tercellular dentinal tubes; 

 b, clear outlines of the dentinal cells. 

 Original. 



PLATE 96. 



Fig. 1. — Side view of upper molars of 

 Manatee (Manatus americanus) : a, in- 

 cisor, | nat. size. Fig. 2. Grinding 

 surface of upper molars. Fig. 3. Side 

 view of a lower molar, nat. size. Fig. 4. 

 Teeth of Tapirus americanus : the dotted 

 lines divide the premolars from the true 

 molars, f nat. size. Fig. 5. Grinding 

 surface of lower molars. Fr. Cuvier. 

 Fig. 6. — Lower jaw and part of upper 



