274 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
facialis) make their exit from the cranial cavity. The prooties arti- 
culate with the exoccipitals and basioccipital behind ; above with the 
pterotics and sphenotics ; internally with the fellow of the opposite 
side ; anteriorly with the alisphenoids and basisphenoid ; and below 
with the parasphenord. 
7. SpHenorics, (Pl. (I. Figs. 1 & 2, Sp0.) 
Or postfrontals, present a flat surface on the roof of the skull, 
but send down a vertical longitudinal plate of considerable thick- 
ness, which is. grooved deeply posteriorly, the arch of the an- 
terior semi-circular canal being contained in the groove. On 
examining the bone from above, there may be seen below the 
surface a channel, a continuation of that already mentioned as 
traversing the pterotic, and containing a mucous canal. About 
the middle of its course on the sphenotic is an opening for a 
mucous pore, with which usually opens also a canal passing from the 
cranial cavity and giving exit to a dorsal branch of the trigemimus, 
though it occasionally opens separately. From the same point an- 
other channel in the bone passes inwards, opening by a pore on the 
line of articulation between the postfrontal and frontal. This also 
contains a mucous canal. On the under surface, near the external 
edge, is a longitudinal groove continued from pterotic which is the arti- 
cular surface for the hyomand. The vertical portion of the bone forms 
the superior boundary of the foramen for the trigeminus and facialis, 
and is not continued forwards to the anterior extremity of the bone, 
which is there formed solely of a horizontal plate. The sphenotic 
articulates with the suwpraoccipital and pterotic posteriorly ; below 
with the prootec ; in front with the alisphenoid ; and above and in- 
ternally with the frontal. 
8. PaRrasPHENOID, (Pl. IT. Fig. 2, PaS.) 
This bone, lying at the base of the skull, extends from the basioc- 
cipital, which it slightly overlaps, to the vomer anteriorly, by which 
it is overlapped. About the junction of the anterior two-thirds with 
the posterior third it expands somewhat, extending upwards to arti- 
culate with prootic. Behind it forms the floor of the small rudiment 
of the canal for the orbital muscles, and its expanded portion is 
firmly anchylosed with the superjacent bone, the basisphenoid. The 
