<3-i >rR. Vr. K. PARKER ON THE STRUCTURE AND 



cartilages (fig. 9, al.sp.) liave coalesced with the ethmoidal tract {al.c) ; here the 

 septum (s.7i.) as it becomes " perpendicular ethmoid " (p-c.) is confluent below with the 

 coalesced trabecular (tr.). On one side the section is seen to pass into the palato- 

 pterygoid band {p-pg.). 



The 5th section (Plate 9, fig. 4), rather more than half" of which is shown, is through 

 the ethmoidal part of the skull propei*, where the nasal cavities (»./>.) are closing in. 

 The perpendicular ethmoid is seen to be very thick, and the trabecula (tr.) to pass into 

 the solid root of the palate- pterygoid bar (p-pg.) from which ascends, suddenly, on 

 the outside, the strong arcuate "orbitar process" of the suspensorium (or.p.). 



The 6th section (Plate 3, fig. 11) is through the solid ethmoid where it closes in the 

 skull, leaving only the olfactory nerve-passages (1) ; here the skull is as solid as that of 

 a Chimcera. The palato-pterygoid bars (p-pg.) are cut through, outside the "post- 

 palatine rudiment" (see Plate 3, fig. 1, pt.pa), whose form, as a gentle elevation, is 

 there shown. 



The 1th section (Plate 3, fig. 12) is behind the palato-pterygoid, and through the 

 fore part of the skull-harge, where the olfactory crura (1) are given off. The cavity is 

 elliptical, the wide wall thick, the roof (anterior " tegmen," t.cr.) and the floor are 

 gently concave. 



On the roof we see the fore end of the frontals (/), and under the floor the 

 parasphenoid {j)a-s.). 



The 8^^ section (Plate 3, fig. 1 3) is behind the "tegmen " and through the fore part 

 of the "fontaneile," covered by the widest part of the frontals [f.) ; the bone below is 

 widening, it is the parasphenoid {pa.s.). The elliptical cavity is deeper, the walls 

 thinner, and the floor is now convex. 



The concavity, below, in the two last sections, is due to the drawing in of the 

 trabecular, and the high, vertical form of the " intertrabecular " tract in the fore skull, 

 is now a bulging floor. 



The 2th section (Plate 9, fig. 5) is through the middle tegmen, between the great 

 median and the lesser paired " fontanelles," and also through the widening parietals 

 (/, by mistake for^j.). Here the roof passes into the wall, downwards; then there 

 is a \iixge fenestra optica on each side, with the optic nerves (II.) emerging; and then 

 the rounded trabeculse, with the bulging " intertrabecular tract," floored by the para- 

 sphenoid {tr., pa.s.). 



The 10th section (Plate 9, fig. 6) is through a lateral fontaneile, the hind part 

 of the parietal (p.), and the auditory capsule, confluent with the basal plate (iv.). 

 The anterior and horizontal canals {a.s.c., h.s.c.) are cut through, and the general cavity 

 of the vestibule (au.) laid open. 



The "tegmen tympani " {t.ti/.) is seen projecting from the outside of the capsule, 

 beyond the horizontal canal ; and the basal plate, or " investing mass," is seen to grow 

 outwards as a floor to the tympanic cavity {ty.f). This plate is deficient, more or less, 

 behind, the capsule resting on an imperfect floor below, and projecting into k fenestra 

 in the wall of the skull. 



