110 SKELETONS OF THE MONOTREMES. 



Fig. 6. Horny "tooth" from the left side of the mandible 

 of the specimen shown in Figures 1 and 2 of 

 Plate XVIII.; reduced; superior aspect. 



Plate XX. 



Fig. 7. Right lateral view of the skull and detached man- 

 dible of an adult male Ornithorhynchus anatin- 

 us. Specimen 1304 Collection Army Medical 

 Museum. Compare with Figure 4 of Plate 

 XIX. (above), Figure 8 of this Plate for the 

 mandible, and Figures 5 and 9 for the skull. 



Fig. 8. Inferior or ventral aspect of the mandible shown 

 in Figure 7; reduced. (See Fig. 4, Plate 

 XIX.) 



Fig. 9. Ventral view of the skull of Ornithorhynchus; re- 

 duced. Same skull as shown in Figure 5 of Plate 

 XIX. (Collection Army Medical Museum.) 



Plate XXI. 



Fig. 10. Left lateral view of the skeleton of an Echidna 

 (Tachyglossus) aculeata. Sex? Slightly less 

 than one-half natural size. No. 2639, Coll. 

 Army Medical Museum. 



Plate XXII. 



Fig. 11. Direct view from above of the skeleton of an 

 Echidna (Tachyglossus) aculeata. Slightly less 

 than one-half natural size. Same specimen as 

 shown in Figure 10 of Plate XXI. of the pre- 

 sent article. 



