DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 83 
hinder of these passages is a great distance from the mid-line, and has a considerable 
(proximal) part of the alisphenoid between it and the proper basis cranii. The 
breadth of the investing mass or parachordal tract behind the pituitary opening is 
nearly equal to that of the cochlez (chl.)—those diverticula of the huge auditory 
capsules. The notch for the foramen ovale (V*.) is against the inner third of the 
cochlea, the squamosal reaches the outer third, and then increases the size of the 
tegmen tympani (¢.ty.), the incus is shown in that space overlapped by the squa- 
mosal. The bulbous cochlez (ch/.) have the appearance in this view of being only 
composed of two coils, for the proximal coil is very large, and the distal is not marked 
off from the second. The outline, even in the inner face, is evident, but the cartilage 
of the capsule has for some distance coalesced with the basal plate (b.0.), that is, along 
its inner edge, from the foramen ovale (V*.) to the opening for the internal carotid 
artery, and then again on to the fissure for the 9th and 10th nerves (for X., XL, read 
IX., X.). The stapes (see also figs. 3 and 6) has been removed from the fenestra ovalis 
and from the incus (7.), and from the latter the primary mandible or malleus (m/ ) has 
been removed. Thus in this figure the pier of the primary mandibular arch, the 
quadrate —or, speaking specially of it as a Mammalian element, the incus—is seen 
inside the posterior radiations of the squama temporis (sq.). Its position here in this 
very simple kind of Mammalian skull is well worthy of consideration. 
If we take the short crus of the incus as the equivalent of the “ otic process” of the 
quadrate, and the long crus as a special Mammalian modification of the incus for 
articulation with the head of the stapes (=extra stapedial process of the columella, see 
in Chameleon, Trans. Zool. Soc., vol. xi., plate 16), and remember that in the 
Mammal the “ orbital process” is suppressed, we shall see clearly what these things 
mean. In all essentials, everything is the same, here, as in the Fow! (Phil. Trans., 
1869, Plate 81). 
The body of the incus, which articulates with the primary mandible, is opposite the 
middle of the cochlea; the long crus runs inwards to join the stapes—or columella in 
this case (see fig. 6)—and the short crus or otic process runs backwards over the stapes 
and fenestra ovalis, so as to get behind the ampulla of the horizontal canal (see fig. 3, 
h.s.c.; and in the Fowl, op. cit., Plate 81, fig. 5, q., h.s.c.). The fenestra rotunda, in this 
figure, is hidden from sight by the small rounded epihyal (e./y.) which is already 
confluent with the capsule ; behind it the facial nerve (VIL) escapes through the stylo- 
mastoid foramen, giving off in its escape the chorda tympani to join the 3rd branch 
of the 5th nerve inside the primary mandible. In spite of the intrusion of the auditory 
capsules, and their tilted position, the cranial nerves make their escape in a very 
orderly manner. Here the facial nerve (VIT.) although thrust far outwards—having to 
bore its way through the forepart of the capsule, from the meatus internus, and then 
travel backwards, under the tegmen tympani, yet manages to escape into the face 
a considerable distance in front of the 9th and 10th nerves ([X., X.). 
The opisthotic region (op.) behind and outside the cochlea is very large, and the 
M 2 
