the ShiU of Diadciiodoii. 301 



skull, and also appears as a small arrow-hcad-sliapcd bone at 

 tlie extreme back of tbc parietal ridge iu a dorsal view of tlie 

 skull (H-. 1). 



Tbe two j)aric'tals ap|)ear to rcniaiu distinct in the skull 

 under consicleration ; they unite in a sagittal suture along 

 the posterior half of the j)arietal crest which separates the 

 great temporal foss;c ; anteriorly they separate very slightly 

 and form the pineal foramen ; it appears probable that their 

 anterior ends were separated by very narrow laminaj of the 

 frontals, and terminated some 3 or 4 millimetres in advance 

 of the foramen, but this is not quite certain (fig. 1). 



For about 1 centimetre behind the pineal foramen the 

 j)arietal is supported on its outer face by a very thin and 

 quite shallow splint of postfrontal (fig. 5). 



The parietal in this region is a gently curved plate of bone 

 falling down on the side of the brain-cavity until it meets 

 the upper border of the columella cranii in a very long 

 suture ; it appears to be certain that this union extends 

 forwards quite to the back of tiic orbit, passing forwards 

 ■well underneath the frontal. Along or just above the junc- 

 tion of the parietal and columella lies a deep well-rounded 

 groove, the anterior part of which is, when perfectly pre- 

 served, covered by a thin lamina descending from the 

 parietals. At a point about I cm. behind the pineal foramen 

 this groove receives a large oval and baekwardly directed 

 foramen, which must lead into the brain-cavity ; this fora- 

 men appears to be bounded below by the columella and 

 pro-otic. Behind this region the parietal is formed by a 

 very thin, almost flat plate which passes outward and back- 

 ward. The upper ])art of this plate is supported behind by 

 the interparietal; lower down it is freely exposed on the 

 posterior surface of the skull and is united by suture with 

 the supra- and exoccipitals ; it forms the upper border of 

 the small post-temporal fossa, and sends down a thin flange 

 outside the fossa in contact with the distal end of the par- 

 occipital process (tig. 4). 



On the outer face this plate is overlapped by a thin process 

 of the squamosal which runs forwards to within 1^ cm. of 

 the junction of the sagittal and coronary crests. On its 

 anterior face this plate is seen to unite with the pro-otic part 

 of the periotic as far back as the post-temporal fossa ; along 

 this junction it bears a deep rounded groove, continuing that 

 found further forwards; this groove opens into the post- 

 temporal fossa (fig. 5). The free edge of the parietal along 

 the sagittal and coronary crests is marked with small muscle 



