20 ^^y- [Vol. IV. 



downward until they meet below the palatine process and then 

 coalesce. Afterward, by the expansion medially of the maxil- 

 laries and the vomers, the portion of the cartilage below the 

 plane of the vomers becomes cut off from the cornua, and forms 

 the unpaired piece that appears so anomalous. But it will 

 require older specimens than those in my possession to settle 

 this matter fully. 



The frontals are long, slender splints which first appear, pos- 

 teriorly, in those cross-sections which pass through the hinder 

 border of the eye. At their hinder ends they are comparatively 

 thick, and overlap the parietals. They lie entirely above the 

 level of the eyes. At the anterior border of the eyes, the 

 frontals descend to near the level of the cartilage overlying 

 the nasal-sac, the lower edge lying a little nearer the middle 

 line than the upper border of the nasal-sac. They may be 

 traced forward as very thin films as far as the perpendicular 

 section just in front of the divergence of the trabecular cornua. 

 Such sections show the anterior end of the cerebrum, and the 

 hinder ends of the two median processes of the premaxilla. (See 

 Fig. 6.) This anterior end of the frontal passes forward over 

 the olfactory nerve, which is directed laterally into the nasal- 

 sac, and the bone may be followed to the anterior border of the 

 nerve. Wiedersheim (o/?. cit., pp. 52-53) has shown that the 

 anterior end of each frontal forms a sort of ring or ferrule 

 {Knochenzwingc) around the olfactory nerve, and through which 

 this nerve makes its exit from the brain-cavity. According to 

 his descriptions, there is a flat process of bone sent down from 

 the frontal on the outside of the nerve ; then in front of this 

 outer process a similar one descends on the inner side of the 

 nerve ; then the two are united under the nerve. Already in 

 my specimens the frontal has come into close relations with 

 the nerve, but has not yet enclosed it by means of its processes. 



The parietal extends from the perpendicular sections through 

 the hinder border of the suspensorium forward to that passing 

 through the anterior border of the lens. It is better developed 

 than the frontals. Its lower border lies upon the upper border 

 of the auditory capsule and trabecula to the eye, where it rises 

 somewhat above the cartilage. In the latter region also it lies 

 somewhat below the hinder end of the frontals. 



Neither the frontals nor the parietals, along their inner or 

 upper borders, approach at all near the middle line. 



