ORGAN OF SMELL IN MAMMALIA. 209 



one, which it appears to encompass. The latter cavity is defined 

 by a well-marked ridge from the prosencephalic part of the 

 cranium. The vomer is deeply cleft posteriorly, and coalesces 

 with the ethmoturbinals. The fore part of the vomer articulates 

 with the median ascending process of the premaxillary arching 

 over the wide vacuities which lead from the nasal passages to 

 the prepalatine apertures. Besides the maxillary sinuses others 

 are developed in the frontals, squamosals, alisphenoids and orbito- 

 sphenoids, with bony septa converging to the rhinencephalic 

 fossae. No nasal sinuses or aircells are developed in the skull 

 of the aquatic beavers. In the voles (Arvicola) a canal leads 

 from the crescentic orifice at the fore part of the antorbital 

 aperture into the lower part of the nasal meatus, above the pre- 

 palatine fissures. In the rat (Mus decamanus) it terminates 

 below the attachment of the anterior turbinal to the premaxillary. 

 In all Muridce the olfactory cavity is very narrow ; the ethmo- 

 turbinal small and but little divided ; the lower turbinal is ele- 

 vated in position. The external nose is short and, as in most 

 Rodents, is clothed with hair save at the middle of the septum. 



In Insectivora the olfactory organ is better developed than in 

 Rodentia. The ethmoturbinal of the mole has not fewer than 

 eight primary lamellae ; but the maxilloturbinal is comparatively 

 simple : the external nose is developed into a snout, Avith well- 

 marked muscles for various and powerful movements. The de- 

 velopment of this part is such in some African Insectivora, fig. 297, 

 as to have earned for them the name of i Elephant-Shrews.' The 

 naked outer border of the nose in the common hedgehog is den- 

 tated : and the edge of the snout is fringed in Condylura with a 

 circle of soft processes. But these, like the still more extra- 

 ordinary dermal appendages in certain bats (Rhinolophus) relate 

 to touch. 



The armadillos and anteaters enjoy an acute sense of smell. 

 In Dasypus sexcinetus the rhinencephalic almost equals the 

 epencephalic division of the cranial cavity : but the olfactory 

 chamber extends backward to beneath the prosencephalic division, 

 and the ethmoturbinals are remarkably extensive and complex : 

 the maxilloturbinal is comparatively simple. The turbinal plate 

 of the nasal almost equals the facial plate in extent. The chief 

 expansion of the cranium is caused by the large olfactory cavity, 

 and the part extending therefrom into the frontals raises them in 

 Chlamyphorus into a pair of domes (vol. ii. fig. 272, a). In most 

 Armadillos the external nose or snout is strengthened by a pair 

 of prenasal ossicles. The rhinencephalic chambers are large in 



VOL. iit. p 



