1901.] LEMUR MONGOZ AND L. RUBEIVENTEE. 261 



large measure towards the formation of the wall of the sinus sphe- 

 uoidalis ; or else this function may be taken over by an intercalar 

 bone makin>i its appearance in the most posterior part of the 

 medial orbital wall and articulating with the same bones as does 

 the "third element*' noticed by Clelaud. 



Gegenbaur states ' that the superficies sphenoidalis of the orbital 

 process, situated behind the latter's superficies ethmoidalis, articu- 

 lates with the body of the sphenoid, from the cavity of which a 

 hollow (" Biichtung") extends on to the sphenoidal surface, and he 

 accordingly figures - a small cavity in this part of the orbital process, 

 almost symmetrical with, but smaller than, the cavity of the 

 ethmoidal surface. 



There is therefore no perfect accord amongst the writers on this 

 topic — Gegenbaur representing as the normal condition wliat by 

 other anatomists is termed an occasional occurrence ; and, like 

 Henle before him, he does not speak of an articulation of the orbital 

 process with the ossicula Bertini, but with the prgesphenoid. 



In Lemurs— Z^Hno- fulvus (" L. mongoz;' B.M. Z. D. No. 60 b), 

 Lepidolemur (see text-figure 67, p. 259), Avahis (see s., text- 

 figure 27, above, p. 132)— I find sometimes present a separate bone, 

 occupying exactly the position of Cleland's " third element " * and 

 Toldt's " Schaltknochen." In one instance at least amongst Lemurs 

 (see below under Lemur rubriventer), the anterior portion of the 

 sphenoidal sinus is annexed in a later staee by a palatal sinus. 



I am likewise inclined to assume that the small cavity in the 

 human orbital palatal communicating with one of the ethmoidal 

 cells is the remnant of the condition in Lemurs, where ethmoid 

 and palatal concur in forming a cavity. From this it follows that 

 the so-called " cellule ethmoidales "are not organites proper only 

 to the ethmoid of Man, and hence are not without phylogenetical 

 importance, as assumed by Seydel *. 



Proceeding now to an examination of the conditions in Lemur 

 mongoz, I find that in all the skulls of this species which I had 

 the opportunity to examine \\\e p)ars perpendicidaris and the orbital 

 process of the palatal diverge considerably from behind forward, so 

 as to enclose between them the posterior triangular portion of a 

 spacious cavity. The divergence of \he pars perpendicularis takes 

 place by its advancing into the cavum nasale from behind forwards 

 in a latero-medial direction, so that the two parts of either side 

 converge slightly towards the middle line (PI. XXII. fig. 10, p.p.) ; 

 each of them terminates freely with a sharp vertical margin, which 

 forms the posterior boundary of the large opening of the cavity 

 into the cavum nasale. The divergence of the orbital process is 

 produced by its being inflated in a lateral direction. The vaulted 



1 0. Gegenbaur, Lehrb. d. Anat. d. Meiischea, 6te Aufl., i. p. 234 (1895). 



2 Op. cit. p. 233, fig. 17C. C. 



3 " Articulating behind with the sphenoid, in front with the ethmoid, inferiorly 

 with the palatals, and sometimes [in Lemurs always— F. M.] above with the 

 frontal." 



^ Morph. Jahrb. xvii. pp. 86, 89 (1891). 

 Peoc. Zool. Soc— 1901, Vol. I. No. XYIII. 18 



