168 ON THE MORPHOLOGICAL CONSTITUTION OF 



portions of the nasal septum. All these relations of the 

 vomer are retained in the remarkably-modified nasal passages 

 and snout in the Cetacea. 



The seat of the olfactory sense is limited to the upper part 

 of the ethmoidal portion of the nasal fossae. However com- 

 plex the arrangement of the ethmoidal turbinal laminae may 

 be, they invariably present the general character of folded 

 laminar neuractinapophyses, connected to their corresponding 

 neurapophyses, after the type of the cartilaginous sessile 

 olfactory cups in the plagiostomes. 



As already stated, the so-called inferior turbinals consist 

 of an antero-posteriorly arranged series or system of mutually 

 abutting hsemactinapophyses, enclosed during development 

 within the nasal fossae. The inferior turbinal system is 

 peculiar to the mammal, and consists of elements which, in 

 developed forms of the system, are derived from, and attached 

 to, the rhinal, vomerine, and ethmoidal haemapophyses. The 

 palate-bone, or distal pre-sphenoidal haemapophysis, supports 

 the posterior extremity of the turbinal system, but I have not 

 had occasion to observe any turbinal element supplied by it. 



As the rhinal sclerotome has disappeared in the bird, the 

 neuro-haemal chambers of the vomerine sclerotome become 

 closed in front, and the external nostrils are supplied by those 

 rnetasomatomic clefts between the vomerine and ethmoidal 

 sclerotomes, which in the mammal form the " incisive 

 foramina," the " canals of Stenson/' and the " organs of 

 Jacobson." 



As the anterior nares are removed one somatome back in 

 the bird, so the posterior nares are removed one somatome for- 

 wards. They are situated between the maxillary and incom- 

 plete palatine arches, theento-pterygoids separating them, while 

 the palatines are on their outer sides. The posterior nares, 

 instead of being directed backwards in a plane at right angles 

 to the axis of the alimentary tube, open downwards in the 



