628 J. TLAYFAIR MCMURRIOH. 



slightly in front of the ectethtnoids anteriorly. They are some- 

 what club-shaped, broadening out posteriorly. On viewing 

 them from the surface they appear to be unsymmetrical, one 

 forming a projection which fits into a corresponding indentation 

 on the other. This want of symmetry is apparent rather than 

 real, for a section (fig. 11, Fr.) shows it to be caused by an 

 overlapping, the portion of bone overlapped being equal to that 

 which overlaps it. Opposite the sphenotics, from the inner 

 surface of each frontal, a process passes down, which articulates 

 with the front edge of the ascending or pro otic process of the* 

 parasphenoid. 



The parasphenoid (fig. 9, Pas.) is a long parostosis, ex- 

 tending from the basi-occipital nearly to the anterior extremity 

 of the cranium on its under surface. Behind it is round, and 

 almost enclosed in the basi-occipital, lying in a deep groove in 

 that bone. More anteriorly it widens out to form a partial 

 floor for the membranous space in front of the basi-occipital, the 

 cartilaginous trabeculee lying immediately above it. At the 

 anterior limit of the postorbital region of the skull (fig. 10) it 

 sends up on either side a process, somewhat triangular in shape, 

 ■when viewed laterally. These articulate with the pro-otics, and 

 along their anterior edges with the descending processes of the 

 frontals. These processes may be termed the ascending or 

 pro-otic processes of the parasphenoid. The space bounded 

 laterally by these two bars, above by the frontals, and below 

 by the parasphenoid, serves for the passage of the orbital 

 muscles and nerves. Anterior to this, in the orbital region, the 

 parasphenoid becomes rectangular, and finally triangular (fig. 

 11, Pa. S.); the apex being directed upwards, having attached 

 to it the lower edge of the interorbital membrane. In front of 

 the orbit it articulates on either side with an ectethmoid, and 

 still more anteriorly (fig. 12) becomes convex, being deeply 

 grooved on the under surface, in which groove lies the vomer 

 (Vo.), almost enclosed, and presenting a similar appearance to 

 the parasphenoid when lying in the groove in the basi-occipital. 

 There is no orbitosphenoid, the passage for the orbital 

 muscles and nerves being very large, appearing, iu fact, almost 



