THE SENSE ORGANS 141 



THE OLFACTORY ORGAN 



The Number and Structure of the Olfactory Ridges 

 and the Turbinals 



Following Broca and Turner, we may divide Mammals, accord- 

 ing to the development of their olfactory apparatus, with especial 

 reference to its cerebral portion [" rhinencephalon," " lobe lim- 

 bique "] into series, viz. : 



[i. Osmatic series, turbinals present and usually five in 

 number.] 



(a) Macrosmatic [organs of smell largely developed], (most 

 Mammals, e.g. Edentata, Ungulata, Carnivora, Eodentia, Mar- 

 supialia, and Lemuroidea). 



(6) Microsmatic [olfactory apparatus relatively feeble] (Pinni- 

 pedia, Whalebone - Whales, 

 Apes, Man, and Monotre- 

 mata). 



[ii. Anosmatic series, or- 

 gans of smell, apparently 

 absent in the adult] (Dol- 

 phins and Toothed - Whales 

 generally, although many of 

 these require further investi- pio> 87 ._ LATERAL VlEW OF THE NASAL 

 gation with regard to this CHAMBER OF A HUMAN EMBRYO. 



point) 1 ^' **' *H' ^ e taree olfactory ridges ; 



f, supernumerary ridge which occurs in 

 The first point to be the embryo ; ., tip of the nose ; pi., 



established is the primitive J-M-ftj - """' '' "" 

 number of the olfactory ridges. 



The investigations of Zuckerkandl lead to the conclusion that 

 the original number of these ridges was comparatively small, and 

 that where, among Mammals, we have a large number or a 

 more complicated form of turbinal, they have been secondarily 

 acquired in the interest of a greater physiological efficiency. 



Most orders of Mammals, e.g. the greater number of Carnivora, 

 Eodentia, Insectivora, Lemuroidea, Marsupialia, with Ornitho- 

 rhynchus (Echidna ?), have five olfactory ridges ; but the Ungulata 



' 1 [Kiikenthal has recently worked out the development of the olfactory organ in 

 the Delphinid*, and has proved (i) that the union of the external nasal apertures 

 is a secondary process occurring during Ontogeny, and (ii) that in the young embryo 

 well-developed olfactory lobes and bulbs are present which disappear in the adult. 

 Denksch. d. medic. -natur-wiss. Gesellsch., Jena, Bd. iii. pp. 326 ct seq.] 



