262 DR. c. I. FORSYTH MAJOR OK [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. 



ou. 



Eight palatal Tiew of Lemur mongoz, showing the large opening («) of the 

 right-side ?iniis into the caviuii 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 («, in 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. The 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 maxillaiy 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 con- 

 sidei-ation 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 pre- 

 molars); and 



