266 



DE. C. I. FOESYTH MAJOR ON 



[Mar. 19, 



the skull. In the orbit (PL XXII. fig. 1) the inflated part of 

 the palatal appears situated medially from the orbital plate of the 

 maxilla, and medially as well as posteriorly from the os planum; 

 the latter helps to form the posterior prolongation of the maxillary 

 sinus and covers besides the anterior prolongation of a sphenoidal 

 sinus, laterally it is in its turn covered by the frontal. 



In this stage the palatal pneumatic cavity rather resembles the 

 swollen orbital maxillary plate above the germs of the molars of 

 young individuals ; so that, if it has ever been seen at all, it may 

 have been mistaken for that pai't of the maxilla. As the figures 

 (PL XXII. figs. 1, 2) show, both parts are lying side by side and 

 are very distinct from each other. With the increase in age of 

 the animal, the palatal pneumatic cavity continues to pervade the 

 orbit in every direction, antero-posteriorly as well as laterally and 

 medially (PI." XXII. fig. 3). Anteriorly, the hinder portion of the 

 maxillary sinus is the loser in the struggle, for it is gradually 

 encroached upon and pushed forward by the palatal sinus ; but I 

 am not avv-are that a communication between the two ca\ities 

 takes place. The palatal cavity becomes, however, enlarged at the 

 cost of another sinus; in a youngish specimen {nt.'S not yet in 

 place) the following can be seen owing to its somewhat damaged 

 condition (see text-fig. 70) : — the before-mentioned sphenoidal 



Text-fig. 70. 



Lemur rubriventer. 



Right orbital region. The bones forming the floor have been partially removed, 

 in order to exhibit the disposition of the underlying sinuses. About 

 I nat. size. 



s.sph. — sphenoidal sinus ; 



: maxillary sinus; s^xi. = palatal sinus. 



sinus (s.sph.), which in the posterior part of the orbit runs 

 parallel to the paktal cavity, medially from it, finally turns round 

 in a lateral direction, ending in a cul-de-sac between the maxillary 

 (s.H?,A-.) and the palatal sinus (s.^xc), thus separating the two. As in 

 later stages I have found no more trace of this cul-de-sac, its 

 place being occupied by the palatal sinus (text-fig. 70), it is evident 

 that it must have been absorbed by the latter. 



