BY R. BROOM. 559 



Fig. 4. — Transverse section of snout of ripe foetus of Miniopterus schreiberdi. 

 Showing the prevomers developing in connection with Jaeobson's 

 cartilage (the modified paraseptal). [In the adult the two 

 prevomers are found anchylosed together to form a median bone 

 which reaches from the one cartilage of Jacobson to the other.] 



Plate XXV. 

 Fig. o.— Under view of skull of IchthyopMs glutinosus. Showing the large 

 median vomer (parasphenoid) and the large paired prevomers 



(vomers). Enlarged. 

 Fig. 6. — Under view of skull of Amblystovia (after Parker), showing the 



very large median vomer (parasphenoid) and the modified 



paired prevomers (vomers). 

 Fig. 7— Under view of skull of ripe embryo of Sphenodon punctatm (after 



Howes and Swinnerton). Showing the small median vomer 



(parasphenoid) and the large prevomers (vomers). Enlarged. 

 Fig. 8. — Semidiagrammatic view of under side of skull of Plesiosaunis (after 



Andrews). Showing the small median vomer and the paired 



prevomers. Keduced. 

 Fig. 9. — Under view of skull of nearly ripe embryo of Zootoca (after Parker). 



The median true vomer is very small, and the paired prevomers 



large. Enlarged. 

 Fig. 10.— Under view of skull of young Tropidonotus (after Parker). The 



median true vomer is almost entirely situated in the anterior 



half of the skull. 



Plate xxvi. 

 Fig. 11. — Under view of skull of Gomphognathus (partly restored behind). 



Showing the median true vomer and the paired prevomers. 



The dotted lines indicate the probable anterior limit of the 



vomer. In a fragmentary specimen of the snout Seeley figures 



a bone which he calls the vomer considerably further forward, 



but the bone which he so regards is almost certainly the 



ethmoid. The posterior extensions of the prevomers are 



assumed. Esduced. 

 Fig. 12. — Under view of skull of Ornithorhynchus. Showing the prevomers 



united to form the dumbbell-shaped bone. Slightly reduced. 

 Fig. 1,3. — Under view of skull of Ptyclwgnatlius. Here only the true median 



vomer is developed, the great palatal development of the pre- 



maxillary having led to the loss of the prevomers. The hinder 



part of the skull is restored. Reduced. 

 Fig. 14. — Under view of skull of Testudo. Only the median vomer is 



developed. The loss of the prevomer may be due to the fact 



that the organs of Jacobson are imperfectly differentiated. 



Nat. size. 



