| OCR Text |
Show 262 DR. C. I. FORSYTH MAJOR ON [Mar. 19 roof of the cavity has invaded the whole bottom of the orbit; bearing in mind what I stated in the above introductory remarks, it may be assumed that the planum, possibly some part of the sphenoid also, shares with the palatal the roofing of this cavity. The sutures having disappeared (text-fig. 69), I must leave this to future investigation. Text-fig. 69. Right palatal view of Lemur mongo~, showing the large opening (a) of the right-side sinus into the cavum nasale. Nat. size. It has been stated above that the medial and lateral walls of the triangular posterior portion of the cavity are formed by parts of the palatal. The anterior portion is triangular also, but the apex is at its anterior end; the walls of this anterior portion are formed by parts of the ethmoid, the medial wall by the basal plate of the maxillo-turbinal, the posterior free margin of this plate, which is concave backward, forming the anterior boundary of the large opening of the cavity. This aperture (a, iu text-fig. 69) therefore has somewhat the shape of a D, placed parallel to the long axis of the skull, the curved part anteriorly ; the vertical part of the D is the posterior margin of the opening. Tbe anterior and lateral walls of the cavity are apparently formed by the planum, the former of the two at the same time marking the boundary between this cavity and the true maxillary sinus, which in this species does not advance into the orbit; nor can I see any communication between the two cavities. The bottom of the cavity under consideration is formed by the bony palate, almost exclusively by the maxilla ; the alveoli of the two anterior true molars protrude into it. The characteristic features of this cavity, as compared with other species, are:- (1) its large opening ; (2) its not being connected with the maxillary sinus (into the bottom of which always protrude the two posterior premolars); and |
