304 PROFESSOR D. J. CUNNINGHAM ON 



Relation of the Superciliary Eminence to the Frontal Air-Sinus. 



That the degree of prominence of the glabellar and supraorbital regions of the human 

 skull is not necessarily determined by the degree of development of the frontal air-sinus 

 is proved by the writings of Bianchi (l), Zuckerkandl (15), Logan Turner (14), 

 and Schwalbe (6, 8, 10). Further, the topographical independence of the area repre- 

 sented by the air-sinus and that occupied by the superciliary eminence is a well- 

 established fact. Two questions, however, of much difficulty remain to be considered : 

 ( 1 ) Can any morphological connection be established between the superciliary eminence 

 and the frontal air-sinus ? and (2) if no such relationship exists between these two 

 factors, what is the morphological significance of the superciliary eminence, and how can 

 its presence in so large a number of the members of the primate group be explained ? 



In considering these problems it should first be noted that where the superciliary 

 eminence fails the air-sinus is also usually absent. We may take the orang as an 

 example of this. As we have noted, there is apparently no morphological equivalent of 

 the superciliary eminence in the orang. It is not correct to say, however, that in this 

 animal the frontal air-sinus is never developed. In the British Museum I had the 

 opportunity of making a tracing of the bisected skull of an adult orang in which a small 

 sinus was present. 



But the absence of the sinus in cases in which there is no superciliary eminence 

 proves very little. On the other hand, we are confronted with the fact that there are 

 numerous catarrhine apes in which the superciliary eminence is highly developed, and 

 yet in which there is not a trace of the sinus. Further, it should be borne in mind that, 

 as Dr Logan Turner has so clearly demonstrated, the sinuses are not infrequently 

 absent in individuals of apparently all races of man. According to this authority, they 

 are absent in 7*5 per cent, of European skulls. 



It would almost appear, therefore, that there is no morphological connection between 

 the superciliary eminence and the frontal air-sinus, and yet when we make a vertical 

 section through the region in one of the lower apes (as, for example, the baboon or the 

 macaque) we see that the eminence is due to a separation of the two tables of the frontal 

 bone and the replacement, between them, of the ordinary diploe by open cancellous tissue. 

 Indeed, the condition is identical to the changes which occur in the young human frontal 

 bone preparatory to the extension into the region of the nasal cavity to form the frontal 

 air-sinus (fig. 1 2). No doubt this is suggestive, but I am afraid we cannot conclude from 

 this fact alone that any clear connection exists between the condition present in these 

 apes and the subsequent step which leads to the formation of an open air-sinus in certain 

 of the anthropoids and man. Still, it is just possible that the condition may indicate in 

 these apes the phylogenetic step by which the sinus formation has been reached. 



If, then, as seems likely, there is no morphological connection to be traced between 

 the superciliary eminence and the frontal air-sinus, how can we account for the presence of 

 the former ? It is not required for the formation of an efficient torus supraorbitals ; 



