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Show 16 PROF. D'ARCY W. THOMPSON ON THE [Jan. 17, this point to the outer margin of the paroccipital ; (3) springing from the upper of the two supra-occipital ridges, a little way before they reach the tubercle and merge together, a ridge curves downwards to another tubercle (s.m.) at the upper and hinder corner of the meatus ; and (4) from this latter tubercle a ridge is continued towards the inferior border of the squamosal or zygomatic process ; the temporal fossa is bounded above by (5) the great curved line which runs from near the base of the line called 3 to the apex of the postorbital process. These lines separate the following areas or fossa?: I, a narrow triangular area, posterior to the auditory region, which gives origin to the main body of the digastric ; II, the temporal fossa, and H I , the small space below the line marked 4, which gives origin to the second portion of the digastric muscle. In the Grey Parrot (fig. 5) we can distinguish all these lines and intervening areas; but the digastric area is much broader than in the Raven, owing to the greater extension forwards of the thin Fig. 5. ;;m. Psittacus erithacus, for comparison with fig. 4. (Letters as in previous figures.) posterior wall of the meatus, and the temporal fossa is much longer and narrower. The line 3, between the digastric and temporal fossa?, guides us to its termination in the suprameatal process of Mivart, which is thus seen to correspond to the tubercle we have marked s.m. in the Raven, in which bird it is some distance behind the glenoid cavity, the intermediate space constituting our fossa III. This last and smallest fossa is excessively small in the Grey Parrot (fig. 6, p. 17), being only represented by a groove between the suprameatal tubercle and the little process of the squamosal internal to it, which descends for a very short distance external and posterior to the head of the quadrate-in other words, which bounds the inconspicuous notch over the head of that bone. To return to Nestor (fig. 6), a comparison of the same clearly marked impressions shows us a still larger digastric and smaller temporal fossa, and leads us to recognize the suprameatal process in that one which is now separated widely from the glenoid cavity by the |