324 DR. P. WOOD JONES ON THE 



By far the most critical and exhaustive account of this region 

 is that contributed by C, I. Forsyth Major to the ' Proceedings' 

 of this Society on Feb. 19th and March 19th, 1901. Here the' 

 os planum of the ethmoid is described and figured in an extensive 

 series of skulls of Lemuroidea. 



In his earlier paper (p. 131) the author says: — " Amongst the 

 Malagasy Lemurs a fairly large os planum " (of the ethmoid) 

 " is present in all the species of Microcehus. In the other genera 

 the planum becomes fused with the palatal at a very early date. 

 A distinct small os planum is often visible in young specimens of 

 Hapalolemur, Chirogale, Lepidolemur, and Avahis, and sometimes 

 in Lemur." But in the later paper the statements concerning 

 Lemur are rather more extended, for at p. 258 the following 

 statement occurs : — "The lateral part" (of the os planum of the 

 ethmoid) " has become united with the palatal at a very early 

 stage; a remnant of the suture with the latter bone is seen in 

 the adult at its antero- medial extremity; in exceptional cases, 

 e. (/., in Lemur catta and young specimens of Lepidolemur, the 

 planum remains completely or almost completely distinct from 

 the palatal." A figure of the orbito temporal region of L. catta 

 leaves no doubt as to the author's meaning. The os planum of 

 the ethmoid is diagnosed as intervening between the lachrymal 

 in front and the palatal behind. 



Here, therefore, we have an admission of the same bony elements 

 as are described by Duckworth ; but their arrangement is depicted 

 in a strangely different order, for whereas Forsyth Major makes 

 the ethmoid coterminous with the lachrymal anteriorly, Duck- 

 worth separates it from this element by a meeting of frontal and 

 maxilla, over an interval of 5 mm. 



Going somewhat further back in the literature of the subject, 

 we find a series of authors denying the presence of an os planum 

 ethmoidale in the orbit of the Lemurs. It was indeed to refute 

 the findings of these authors that Forsyth Major published the 

 papers from which the above quotations have been made. 



The French zoologists, for the most part, have denied the 

 presence of this element, and probably in this they have been 

 guided or assisted by their intuitive discrimination which sees 

 little but superficial resemblance between the Malagasy Lemurs 

 and the Anthropoidea. Ouvier declared that the os planum of 

 the ethmoid was in the Lemurs altogether enveloped by the 

 frontal and the palatine, and therefore did not appear as an 

 element in the wall of the orbit. 



MM. Grandidier and Alphonse Milne Edwards regarded the 

 os planum as being overlain by the frontal which therefore came 

 in contact directly with the maxilla. Obviously Flower came to 

 the same conclusion, for he says, "The os planum of the ethmo- 

 turbinal does not enter into the inner wall of the orbit, but is 

 shut out by the maxilla.'"' 



In this cursory survey of the literature we have therefore four 

 distinct diagnoses of the elements entering into the formation of 



