OCR Text |
Show 28 PROF. D'ARCY W. THOMPSON ON THE [Jan. 17, curved prefrontal processes approach very close to the postfrontal ; it is complete in the others, and its posterior portion is somewhat broad and flattened, especially so in A. rnacao, where the broadened hinder region forms an obtuse postero-inferior angle. Fig. 19. Ara cliloroptera (reduced). The squamosal process is least developed in A. ararauna, most so in A. maracana. The paroccipital wings are largest in A. chloroptera and macao. The auditory meatus is widest in A. chloroptera and maracana ; it is considerably narrowed, and shows a slightly projecting lower lip and a well-marked postero-superior notch in A. ararauna ; and in A. macao it is very remarkably narrowed, partly by the growth forwards of the posterior wall, and still more by the growth backwards of the anterior, which overlaps the lower part of the orifice as a broad tongue of bone. The two heads of the quadrate (fig. 20) are in all more widely separate than in Quadrate bone of Ara, cliloroptera. A. hyacinthinus. The anterior margin of the infraorbital septum is squarely truncate in A. ararauna; it tends in the others, and especially in A. macao, to curve forward in the same manner ?s though in a less degree than, in A. hyacinthinus. The mandible is narrowest from side to side in A. ararauna, and in this respect least like that of A. hyacinthinus. In the same species the articular groove for the quadrate is nearly straight |