600 CLASS XVII. 



transmit the branches of the first pair of nerves to the nasal cavity 1 , 

 and in the sinuses, subsidiary cavities, usually divided into mutually 

 communicating cells, which exist in the frontal and sphenoid 

 bones and the superior maxillary bones. The mucous membrane 

 that covers these cavities is thinner than that of the nasal cavities, 

 and receives no branches from the first pair of nerves 2 . Although 

 they cannot themselves be the seat of smell, still they have the 

 greatest extent in those mammals whose sense of smell is most 

 acute. All mammals do not, like man, possess these three differ- 

 ent cavities simultaneously. In the edentates, for instance, the 

 frontal sinuses are wanting ; those in the sphenoid bone are com- 

 monly much smaller than in man. The largest frontal sinuses 

 occur in the elephant, in which they not only extend to the parietal 

 and temporal bones, but even to the articular condyles of the occi- 

 pital bone. The bony parts of the nasal cavities are further com- 

 pleted by cartilages, which in some mammals form a case, or are pro- 

 longed into a moveable snout as, for example, in the hog, the mole, 

 &c. Above all, the proboscis or trunk of the elephant is remark- 

 able, which contains two such tubes in the interior, that extend 

 throughout the whole length of the organ. Thick nervous branches 

 are distributed to the proboscis which arise from the suborbital 

 nerve of the second branch of the fifth pair. Many muscular bun- 

 dles, of which the innermost run transversely and pass by their 

 tendons between the exterior longitudinal fibres to the skin, give 

 motion to the trunk 3 . In the true cetaceans there are no accessory 

 cavities in the cranial bones in connexion with the nasal cavity. 

 The nasal cavity ascends nearly in a straight direction to the upper 

 part of the cranhim, where the external double or single nasal aper- 

 ture (the so-named blow-holes) are situated. Near these apertures 

 on the upper part of the cranium are two sacs covered by mucous 

 membrane, folded longitudinally and of a black colour, which is 

 regarded as the olfactory organ of these animals, but which receives 

 its nerves from the ophthalmic branch of the fifth pair only 4 . 



1 Compare above, p. 570, as also on the concha. 



2 Compare BLUMENBACH Prolusio acad. de sinibus frontalibus, G-ottingae, 1778, 4to. 



3 CUVIER Le$. d'Anat. comp. n. pp. 665 667, and especially v. pp. 283 -289 ; 

 comp. ibid PI. xxix. 



4 CAMPEE Cetaces, pp. 148 150, PI. 48, fig. i; G. SANDIFORT Bijdragen tot de 

 onllcedkundige Icennis der walvisschen, cited above, see p. 587. 



