1901.] 



SKULLS or LEMUKS AND MONKKYS. 



131 



p. 136), Galcujo (text-figs. 34, 36, 38, 39, pp. 138, 139), possess a 

 large os planum, which very otten is not e\^en limited to the orbit ; 

 it seems to have been overlooked because in older individuals the 

 sutures within the orbit disappear, as indeed is the case with 

 almost all the cranial sutures. Amongst the Malagasy Lemurs a 

 fairly large os planum is present in all the species of Microcehus. 

 In the other genera the planum becomes fused with the palatal 

 at a very early date (text-figs. 28 & 37). A distinct small os 

 planum is often visible in young specimens of Hapalolemur, 

 Chirogcde, Lepidolemur, and AvaJiis (test-fig. 27), and sometimes 

 in Lemur. Chiromys is the only Lemur in which I have not been 

 able to trace the planum (text-fig. 2Q). 



Text-fis. 26. 



■^nct-. I'Tzs, 



focc 



C^S..-- 



Orbital region of Chiromys madagascariensis. Nat. size. 



OTa.M?s. = insertion of the malar on the maxillary; wiw. = malar ; wa% = maxilla ; 

 I. = lacrymal ; fl. = planum ; as, = alisphenoid ; os. = orbito-sphenoicl ; 

 /n=frontal; ^«. = palatal ; .r. = intercalar bone ; i'i.=intercalar bone. 



In a general manner we can state that in those Lemuridse which 

 are provided with a large lacrymal, the os planum is reduced ; 

 vice versa the lacrymal is reduced or absent — at least from the 

 orbit and the outer surface of the cranium — in those Lemurs 

 which are pro\ided with a large os planum. ]j\irther particulars 

 with regard to this bone will therefore more suitably find their 

 place in connection with the description of the lacrymal. Sketches 

 of the OS planum in various Lemurids are given in the fext- 



9* 



