92 
MR. W. K. PARKER ON THE STRUCTURE AND 
interhyal has not appeared, up to this time; but abortively developed parts are often 
late. The inturned neck of the incus is curiously alate. The base of the stapes is 
very thick. 
The distal parts of the hyoid arch (Plate 12, fig. 3) have undergone little change 
except as to size and solidity (see Plate 11, fig. 5); but the thyrohyals ( t.hy .) are 
more incurved, for clasping the larynx. 
The end view (Plate 12, fig. 2), as compared with the same aspect of the skull in 
the early stage (Plate 11, fig. 4), shows considerable progress in development. 
The thick parietals (p.) almost meet to finish, with the supraoccipital, the 
lambdoidal suture. The squamosals (sq. ) now show considerably from the end ; they 
have gained much substance, and are large convex plates. 
The upper half of the face of the great occipital arch has its middle third occupied 
by a supraoccipital bone (s.o.), shaped roughly like an hour-glass; it does not yet 
reach the foramen magnum ( f.m .), but the fenestra (or fontanelle) over that doorway 
is now a mere notch in the lower edge of the cartilage. 
Nearly half the space from the lower edge ‘of the bony supraoccipital to the 
occipital condyles ( oc.c .) is occupied, below, by the large spreading exoccipitals ( e.o.). 
Their upper margin is sinuous, their outer rounded, and the large outer margin runs 
over the opisthotic convexity. Below, each bone runs in as an uncinate tract, 
between the opisthotic and the condyle; the thickisli, convex, outer edge of the tract 
is the low, indistinct paroccipital process. The opisthotic tract, which has taken the 
form of the enclosed posterior canal, must he conceived of as lying some distance from 
the eye (see also Plate 11, fig. 8), and the bulbous cochleae (chi.) as still further off. 
This stage is further illustrated by a vertically longitudinal section, made a little to 
the left of the mid-line in the fore half (Plate 13, fig. 12). 
We see at once in this figure what is also seen in the side view (Plate 11, 
fig. 7), namely, that the snout and fore part of the nasal capsule is considerably 
curved downwards. I only see that in this stage and in this species, and am not sure 
whether there is some specific modification in this case ; at any rate, this skull thus 
repeats a character seen well in Cycloturus (Plate 10, fig. 7).* 
The ethmoseptal or front half of this skull is one-fourth longer than the proper 
basiscranii or spheno-occipital region. In the early stages they were equal. 
Nowhere is the intertrabecula, or thick base of the great partition ( p.e., s.n.), more 
distinct and massive than in this; but for its crest, it would be almost Cetacean.! 
* These lesser modifications, both as seen in species and in stages, are almost endless, and yet none of 
them is without signification. The two nine-banded Armadillos differ in this respect, for Tatusia peba 
(Plate 5, fig. 6) has a very straight snout, whilst the closely related Tatusia hybrida has it considerably 
decurved (Plate 2, figs. 1 and 8, and Plate 6, fig. 3). 
f See Eschricht’s figure of the shull of an embryo of Balcena japonica in a posthumus paper published 
by the late Professor Reinhardt: r ‘Ni Tavler til Oplysning af Hvaldyrenes Bygning,” tab. ii., Copen¬ 
hagen, 1869. 
