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DR. W. WOOD JONES ON THE 



calta B.M. 59 c (figs. 61 & 62, p. 256) will show that it is this 

 anterior inflated portion of the palate which is diagnosed as the 

 os planum of the ethmoid. Concerning the inflation of this part 

 of the orbital wall Forsyth Major says : " It (the so-called os 

 planum of the ethmoid) "always forms the roof of a pneumatic 

 cavity, which often (L. catta, L. macaco, L. varius) is but an 

 appendix of the maxillary sinus. The anterior portion of the 

 palatal also participates, as a rule, in the formation of this 

 pneumatic cavity, by forming its posterior cul-de-sac." As a 

 matter of fact, it is this variability of the posterior extension of 



Text-figure 4. 



Orbito-temporal region in the foetal skull of _L. albifrons X L- melanocephala. 

 Length 41 mm. Lettering as in text-fig. 3. 



the inflated area that produces the variability of the presumed 

 suture-line. The bones of the orbital wall are particularly thin 

 and transparent in the Lemurs, and in adult examples the septa 

 between air-chambers may be far more conspicuous than actual 

 suture-lines. This condition is carried to extremes in old spe- 

 cimens of some types, such as Galago, in which the whole of the 

 orbital wall (and of other regions of the skull) has the appearance 

 of cracked ice, each crack corresponding to a bounding wall of, a 

 small sinus, and the whole creating such a meshwork of lines 



