26 
MR. W. K. PARKER OX THE STRUCTURE AXD 
(Plate 33, fig. 3) shows the hugh orbitosphenoid as separate from the auditory 
capsule. It is so, afterwards, and in the 4th Stage (Plate 34, figs. 5, 6) I have given 
perfectly correct figures. In the 3rd Stage the sections show the continuity of these 
tracts (Plate 32, fig. 6), but this upper tract was considered by me as part of the 
supraoccipital roof. On the left side of the figure referred to, the cartilage (s.o.) should 
have been lettered s.a.c. —“supra-auditory cartilage;” on the right that tract also 
lettered s.o. shows where the cartilaginous wall is passing into the occipital roof. My 
views as to the morphological meaning of some of the parts will be seen in this Paper 
to have undergone some change ; I give here my last deductions. 
I have not cumbered my description with mere details, although the actual sections 
tempted me to give a much more detailed account of the structures displayed in them. 
A comparison of the figured sections with the figured dissections will make everything 
plain, as every part may be identified and compared in the two sets of figures. 
Dissection of the skull of Tatusia hybrida.— Second Stage (embryos, 2 in., and 2-| in. long). 
This skull was dissected so as to leave all the investing bones in situ (Plate 2, 
figs. 6-8) ; part of it is shown as dislocated to display the hinder end of the mandible 
and the tympanic region (Plate 6, fig. 8). The endrocranium may be considered as 
altered very little since the last stage ; the embryos, dissected, measured, not including 
their tail, the one 2 inches, and the other 2^ inches in length. 
This somewhat more advanced stage is very valuable, however, with regard to the 
endocranium, for the bony centres formed in the cartilage are more perfect—not mere 
calcified tracts. 
The lower view (Plate 2, fig. 6) shows the peculiar position of the outer nostrils 
(e.n.), namely, quite on the ventral aspect of the face; the Armadillos are terricolous 
in their habits. Behind and between the coiled valvular processes (al.n.,n.v.) the basal 
part is bilobate ; from the back part of the double tract the protecting cartilages of 
Jacobson’s organ (fig. 1, rc.c.) arise. In this figure they are hidden to some extent 
by two small bones lying one on each side of the mid line (v\ ; see also Plate 3, 
figs. 7, 8). These are the anterior paired vomers ; they are thin, long shells of bone, 
concave within and above. Outside these the small premaxillaries (px.) are seen ; 
they are notched below, and have no palatine process. 
These parts lie in an angular space formed by the fore part of the huge maxillaries 
(fig. 6, mx.); these latter bones have several well-marked regions ; they extend from 
the premaxillaries to the zygomatic arch (j.), and then fork, behind, so as to enclose the 
fore margin of the open orbital floor. A long suture unites the two bones at the mid 
line, and outside this there are two parts of bone divided by a furrow which runs 
almost parallel with the median suture. Thus the palatine part is sub-distinct from 
the flange that grows from the alveolar region, with its double wall, its intervening 
imperfect tooth-sockets, and developing teeth. The maxillaries are scarcely seen from 
