ORBlTO-TEMPORAL REGION OF SKULL OP LEMUR. 323 



24. The Structure o£ the Orbito-teinporal liegion of the 

 • Skull of Lemur. By F. Wood" Jones, M.B., D.Sc, 

 F.Z.S. 



[Received and Read November 20, 1917.] 



(Text-figures 1-5,) 



Index. 

 Steuctuee and Moephologt pp. 323-329 



The question of the structure of the orbito-teniporal region of 

 the Lemurs is one that has by now accumulated a very bulky 

 literature ; and this fact is, in itself, almost a guarantee that some 

 difficulty and uncertainty is attached to interpreting appearances 

 which are open to ordinary inspection in the skulls of animals 

 that are neither particularly minute nor particularly rare. 

 The uncertainty is at once made apparent by a study of this 

 literature ; for very difierent accounts are given of the elements 

 which enter into the composition of this limited portion of the 

 skull. But another factor may be detected, and this is a rather 

 more subtle one than any mere difficulty in recognising ill-marked 

 suture-lines. It is obvious that some have wished to see an 

 ordering of the bones upon lines indicative of a Primate kinship, 

 while some have neither looked for, nor expected, any indications 

 of such affinity. 



The observations recorded here were made upon two full-term 

 foetuses — the one of Lemur catta, and the other a hybrid between 

 L. alhifrons S and L. melanocephala $ , both born in the Gardens 

 of this Society. Beyond the limits of these two representatives 

 of the genus Lemur the present inquiry is not extended so far as 

 the study of foetal material is concerned. The question that has 

 been an outstanding one for now nearly a century is the presence 

 or absence in the orbital wall of an " os planum " or " planum 

 orbitale" of the ethmoid bone. If we turn to a recent woi"k 

 (' Morphology and Anthropology,' by Dr. W. L. H. Duckworth, 

 1915), we find the following as a description of this region in 

 Lemur: — "On the inner orbital wall, the frontal and maxillary 

 bones join along a suture for a distance of about 5 mm., and thus 

 widely separate the ethmoidal from the lachrymal bone " (p. 73). 

 The condition here described depicts' a phase only separated 

 by degree from that prevailing in the Anthropoidea, and the 

 description leads one to suppose that the lachrymal in the fore 

 part of the orbit is separated from the os planum of the ethmoid 

 in the hind part of the orbit by the meeting of the frontal and 

 maxilla from above and below over the intervening interval 

 of 5 mm. The figure that accompanies this description lacks 

 definition in some of its index lines ; but apparently it bears out 

 this diagnosis of the disposition of the elements. 



