i92 MR. W. K. PARKER ON THE STRUCTURE AND 



Tlie roofs {(d.n.) are narrow crescents and only foi-m a tract half the width of the 

 floor (fig. 2) ; the septum (s.n.) is thick, and ends as a blunt mass, not projecting ; the 

 pro-rhinals (fig. 2, jf-i'h.) are rather small and inturned ; the angles of the original 

 cornua pass well into the maxUlaries (fig. 2, inx.). 



From the upper surface of these angular growths a thick and widish crescent of 

 cartilage grows up as a limited nasal wall (figs. 1, 3), behind the nostril (e.n.), and 

 confluent with the roof (al.n.). 



The two pairs of labials {u.P.n.l-.) that defend the nostril in front, are rather small. 



The palato-suspensorial arch is normal but very strong, and the usual bony plates, 

 namely, the falcate palatine ( j^a.) and the tru'adiate pterygoid {x>g-), are normal, and 

 leave an average amount of cartilage untouched. But the condyles of the pedicle and 

 the quadrate {i^d., q.c.) are very large and solid, and the latter region is partly ossified. 



The cai-tilage is left uncovered towards the end of the pedicle, wliich is not only 

 very soHd, but is also almost external in position. Moreover, the pterygoid bone forms 

 a right angle by its fork, and in the space thus half enclosed there is an extremely 

 large, circular Eustachian opening (cm.), whose boundary is finished by the hind process 

 of the pterygoid, by the stylo-hyal, and by the binding web of fibrous tissue tying 

 these together. 



The mandible (fig. 3) is normal ; the dentary (d.) is half the length of the ramus ; the 

 mento-Meckelian {m.mk.) is large, and the coronoid process (ar.) low. The anmilus 

 {'(.t;/.) is relatively almost as large as in Rana pipiens (Plate 8, fig. I), but it is widely 

 open above (fig. 3) ; yet the drum, altogether, is large and well specialised, and its 

 additional structui-es are neai'ly typical. 



The stapes (figs. 4, 5, (5, st.) is oblique, truncate, and lobate ; it is gently convex 

 externally, and gently concave within. 



The columella has a reniform proximal osseous centre, wliich hardens most of the 

 dilated upper end ; this is the inter-stapedial {i.st.) ; it is segmented from the long 

 medio-stapedial rod {m.st.) by separate ossification, and not by separation of the 

 primary cartilage. The distal cartilage is as long as the bony part (m.st.) ; the extra- 

 stapedial {e.st.) is a compressed tongue, which gives off" a ligulate supra-stapedial (s.st.) 

 that is confluent with the ear-mass above. So also is the stylo-hyal (st.h.) confluent 

 above ; it becomes first bi'oader, and then narrower again as it passes round, without 

 lobulation, to become hypo-hyal (see Plate 15, fig. 8, c.hij., h.hi/.). 



The body {b.h.br.) of the basal tract is only two-tliirds the extent of the notch in 

 front ; it has no anterior lobe, and the posterior lateral lobe is long, pointed, and 

 diverging. The bony thyro-hyals {t.hy.) are normal, but in front of them the basal 

 plate is occupied in its centre by a large basi-branchial endostosis {b.hv.). Also on each 

 hypo-hyal there is a small oval extra-hyal piece (e.hy.). 



The investing bones are normal as to strength, but they dififer very much in certain 

 regions from the norma: the fronto-parietals {/■]>■) (.-over two-thirds of the inter- 

 auditory region, the right overlnpping tlic left. 



