ORGAN OF SMELL IN MAMMALIA. 



207 



part of the rhiiiencephalon, are continued clown to this tract ; 

 but it is principally supplied, like the lower turbinal, by the naso- 

 palatine nerve. 1 



Characteristic of the mammalian organ of smell is the great 



O a 



provision made by bony and gristly laminae for the support 

 of the olfactory membranes. The original extent of these primi- 

 tive capsules is augmented, as in a branchial organ, by manifold 

 plicae and processes, usually so curved and contorted as to suggest 

 the resemblance to turbinate univalves. The neurapophyses 

 transmitting the nerves of the nasal segment of the skull 

 are reduced, as has been shown, in Mammals, almost to their 

 essential function ; as such they appear in Celacea (vol. ii. 

 p. 421, fig. 287, H ). So reduced and withdrawn from outward 

 view, they are further masked in the rest of the class by 

 the agglutination thereto, or outgrowth therefrom, of the turbinal 

 olfactory capsules : the whole, as agglomerated in them, receiving 

 the name of ( sieve-bone ' (ethmoid), from the exceptional pecu- 

 liarity of the number of olfactory nerves in the Mammalian class. 

 In fig. 153 is given an oblique view of this complex bone 

 with the anchylosed sphenoid in the Hog. The confluent mesial 



153 



Osseous parts of olfactory capsules. Hog. 



laminae of the prefrontals project as ' crista galli ' dividing the 

 rhinencephalic fossae : to the under or outer part of the cribriform 

 or perforated laminre of the neurapophyses the parts of the 

 olfactory capsules called < labyrinths,' q, and ethmoturbinals, .9, 

 are anchylosed : the maxilloturbinals, p, remain longer distinct, 

 and ultimately coalesce with the superior maxillaries. The con- 

 volute plates attached to the roof of the nasal chamber, fig. 157, /;, 

 here called ' naso-turbinals,' are in most quadrupeds added to 

 those shown in figs. 152 and 153. 



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