146 MR. W. K. PARKER ON THE STRUCTURE AND 
seen, even above, to be creeping into the ale, the bony centres of which just touch the 
foremost of these extensions of the basisphenoid. But more than a third of the hind 
part of the ale is still cartilaginous ; the posterior external part dips below the 
auditory capsule, just as the front margin does under the orbitosphenoid. 
The sphenoidal fissure (V'*.) is an oblique reniform foramen, and to it a groove 
for the 2nd branch of the 5th nerve runs from the large foramen ovale (V*.). A small 
sphenotic flap of the auditory capsule overlies the alisphenoid, externally ; between 
this part and the coiled cochlea the facial nerve (VII.) escapes, running first under a 
bridge of cartilage from the foremost hole of the meatus internus (VII., VIII.). The 
swellings outside the wall—which has been cut away horizontally—are due to the 
horizontal and posterior semicircular canals (h.s.c., p.s.c.), the arch of the anterior canal 
(a.s.c.) is cut away and its cavity exposed. The hollow for the flocculus is not well 
shown in this view; behind it, the opening of the ‘“ recessus labyrinthi ” is seen. 
Patches of bony cells are now to be seen, the beginnings of the extensive opisthotic 
bone (op.). These are at the hinder margin of the cochlea in the lower view (fig. 1). 
This bony deposit is to be seen, inside, in front of the large foramen for the 9th 
and 10th nerves (IX., X.). This foramen and the condyloid (XII.) in front of it are 
seen in the upper view with the exoccipital (¢.0.) creeping up to the latter; the large 
six-sided basioccipital (b.0.) still lies in the centre of the large multiangular basal 
cartilage, flanked, outside and behind, by the occipital condyles (oc.c.). 
Visceral arches of Third Stage. 
The outer and inner elements of the mandible (Plate 22, fig. 5) are still bound up 
together, and are nearly equal in bulk. The new condyle on the “ramus” is at no great 
distance in front of the primary morphological condyle 
the short crus of the incus (2.). 
This suspensorial segment is still unossified, and so is the stapes (st.) or uppermost 
part of the next arch; but the malleal bony centre (ml.)is working into the cartilage. 
The dentary (d.) has grown over MecKEL’s cartilage (im.) in one place, and is con- 
verting that part into bone; in front of this ensheathed part the rod is very solid ; 
its basal bar (b.1n.) is well formed, and turns upwards somewhat. The cartilaginous 
ends of the three hind lobes of the ramus keep growing, part passu, with the rest ; 
the annulus tympanicus (@.ty.) is now ossified. 
The hyoid arch has been cut away where the epihyal (Plate 22, fig. 6., ei.) is con- 
fluent with the auditory capsule (see fig. 3). The cartilaginous segments are solid and 
strong, but are at present quite unossified. 
Fourth Stage of the Skull of Evinaceus europeus ; young specimens, 2 weeks old ; 
3 inches long. 
This stage shows but little difference in the general form and condition of the endo- 
cranium ; but the osseous centres are much more advanced (Plate 19, figs. 3-5). I have 
