142 



THE STRUCTURE OF MAX 



have, as a ride, more than five, and sometimes as many as eight. 

 The Edentata possess from six to eleven (Orycteropus has eleven, 

 Dasypus nine, Bradypus and Manis seven, Myrmecophaga six), 

 and the Primates from one to three. 



At a late embryonic period three olfactory ridges are often 

 present in Man, inasmuch as between the superior and inferior 

 a third projects into the lumen of the nose (cf. Fig. 87). 

 This last, when present, is more or less distinct at birth, but 

 it becomes reduced later, the superior ethmo-turbinal, as a 

 rule, growing over it like a cover. With this superior ethmo- 

 turbinal, which must be considered as primary, the rudiment 

 of a fourth is found (cf. Fig.) ; but this is further differentiated 

 only in exceptional cases. We thus have at least four ethmo- 

 turbinals represented in the developing human nose, with three 

 olfactory meatuses; and this arrangement recalls those Mammals in 

 which there are four corresponding ridges present in the adult. 



[Concerning variation of 

 the olfactory meatuses of 

 the human adult, on recent 

 examination of 152 indi- 

 viduals, 1 the dominant con- 

 dition presence of three 

 was observed in 56 per 

 cent; four were noted in 

 41 per cent, and five in 

 n1 '- 1'3 per cent. In three 

 r iL instances (i.e. approximately 

 in 2 per cent) only two were 

 found, the superior turbi- 

 nated bone being absent; 



and in one of these " there 

 FIG. 88. SAGITTAL SECTION THROUGH THE i . i i , f 



NASAL AND BUCCAL CAVITIES OF THE was . a horizontal plate of 

 HUMAN HEAD. cartilage projecting into the 



/, II, III, the three olfactory ridges ; sn'., frontal nfle! ol fr,n f f V,o 



sinus ; sn"., .sphenoidal sinus ; os., opening of n&Sal tOSSa r m the se P tlun 

 Eustachian tube ; be., entrance to the mouth ; On a level with the inferior 



>ra ; v.u., axis turbinated bone."] 



When it is further re- 

 membered that the maxillary, frontal, and sphenoidal sinuses 

 (sn'., sn"., Fig. 88) are also lined by olfactory mucous membrane, 



1 [Made under the auspices of the Collective Investigation Committee of the 

 Anatomical Society of Great Britain and Ireland. See Jour. Anat. and Phys 

 vol. xxviii. p. 73.] 



