274 PROCEEDINGS OF THE CANADIAN" INSTITUTE. 



facialis) make their exit from the cranial cavity. The prootics 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 parasphenoid. 



7. Sphenotics. (PI. II. Figs. 1 & 2, SpO.) 



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 trigeminus, 

 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 said 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 sup-aoccipital and pterotic posteriorly ; below 

 with the prootic : in front with the alisphenoid : and above and in- 

 ternally with the frontal. 



8. Parasphenoid, (PL II. 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 anchyiosed with the superjacent bone, the basisphenoid. The 



