200 
MR, W. K. PARKER ON THE STRUCTURE AND 
the middle tract, which bulges inwards, the “ sinus ” or common tube of the anterior and 
posterior canals. The latter is in the convexity that is just seen behind in the great 
space for the lateral sinus ; the hollow oval space between the first and second 
arched convexity is for the “ flocculus cerebelli.” Where the antero-inferior and 
postero-superior regions of the capsule meet, there, above, the inner and outer openings 
of the short tunnel for the portio dura (VII.) are seen. 
Below these holes the perforations for the portio mollis (VIII.) are seen in the 
short arched meatus internus, and the space between the capsule and the basi- 
occipital leads to the foramen lacerum posterius. There the outline of the capsule is 
gently concave; in front of that part it swells again with the coils of the cochlea 
(chi.), and behind it with the galleries of the vestibule (■ vh .). The halved occipital 
arch is much narrower than the capsule in front of it; we see tire supraoccipital ( s.o .) 
and the exoccipital (e.o.) already large centres ; the condyloid foramen (XII.) and 
the articular condyle ( oc.c .) are both clearly seen in this view. 
The investing bones are rapidly forming; the nasal (n. ) above the septum, and the 
vomer (v.) below; and the maxillary and palatine (mx. pa.) below the nasopalatine 
passage ( n.p.c.) are seen edge-wise. 
The frontals (/.) are no larger than those of a Snake, but the parietals (p.) are 
very large ; and project from the outside, at the upper third of the front lateral 
fontanelle, yet they fail to meet the small, low-lying squamosals (sq.), and there, 
between them and behind the alisphenoid, there is a large pyriform tract entirely 
unsupported, either by cartilage or bone. 
In a dissection of the basis cranii at this stage, seen from below (Plate 30, fig. 18), 
we get further light upon the parts just described as seen in the inside of a halved 
skull. The cartilage of the snout (al.n.) is represented in this figure as detached 
from the sides and roof of the septal region, but having the inferior tracts that grow 
from it, namely, the recurrent cartilages ( rc.c .) attached. These remarkable capsules, 
that contain Jacobson’s organs, arise as aim from the base of the septum in the lower 
and hind part of the snout, then expand into horizontal laminae, and then form a hook 
round the opening of Jacobson’s organ, enclose it entirely for a short distance, and 
then only on the internal and lower side, thus forming a long cochleariform tract 
which reaches half-way to the pituitary space (py.). On the inside of these cartilages 
the palatine processes of the premaxillaries (p.px.) run ; they are thin vertical plates, 
and show no separate antero-lateral vomer attached to them. The Mole has the same 
deficiency. 
The vomer, proper, (v.) is long and normal; it is pointed in front, and slightly split 
behind. Behind the sheathing vomer the intertrabecular bar widens, it is first 
ethmoidal (p.e.) and then becomes the presphenoid ( p.s .). 
On each side I have figured the hind, closing part of the lateral ethmoidal regions 
(nf.) ; the primary form of the so-called “sphenoidal sinus,” which has wedged in 
here between the alisphenoid (al.s.) and the base of the great orbitosphenoidal tracts 
