202 



COMPARATIVE ANATOMY 



A large gland whicli, opens at the boundary between the inner 

 and outer nasal cavities lies within the turbinal. Below the latter 

 is the aperture of the lachrymal duct : this duct in some Reptiles 

 opens on the roof of the pharynx (Ascalabota), and in others into 

 the internal nostrils (Ophidia). 



The structure of the nose in Chelonians is very complicated and varied. 

 In marine Chelonians it is divided into two passages, one above the other, 



and connected by means of a perforation of the 

 septum. The comparative paucity of glands in 

 the olfactory organ of Lizards and Snakes forms 

 a marked contrast to the condition seen m 

 Chelonians, the nasal organ of which is charac- 

 terised by a great abundance of them. 



The extension downwards and back- 

 wards of the olfactory organ is most marked 

 in Crocodiles, iu correspondence with the 

 growth forwards of the facial region and 

 the formation of the palate ; its posterior 

 part thus comes to lie below the brain 

 and base of the skull. Each nasal chamber 

 is divided posteriorly iuto two superim- 

 posed cavities, the upper of which repre- 

 sents the proper olfactory chamber, and is 

 lined by sensory epithelium, while the 

 lower functions as a respiratory portion 

 only. Certain accessory air-chambers are 

 connected with 'the nasal cavity. A large 

 gland is present between the olfactory 

 chamber and its investing bones, and opens into the nasal cavity. 

 As in other Reptiles, there is only a single true turbinal, but ex- 

 ternally to it lies a second prominence, which may be spoken of as 

 a pseudo-turbinal. 



Fill. 161. — Diagram of the 

 Olfactory Organ of a 

 Lizard. (Longitudinal 

 vortical section.) 



AN, IN, outer and inner 

 nasal chambers ; +, tube- 

 like connection between 

 them ; Ch, internal nos- 

 trils ; P, papilla of Jacob- 

 son's organ ; Ca, aperture 

 of communication of the 

 latter with the mouth ; 

 MS, oral mucous mem- 

 brane. 



Birds. — In all Bii'ds, as in Lizards, there is an outer chamber, 

 lined by stratified epithelium, and a proper olfactory chamber, 

 situated above the former. Birds also possess only a single true 

 turbinal — if by this term is understood a free independent projection 

 into the nasal cavity supported by skeletal parts. Two other pro- 

 minences (pseudo-turbinals) are, however, present ; one of which lies, 

 like the true turbinal, in the proper olfactory chamber, while the 

 other, like the pseudo-turbinal of the Crocodile, is situated in the 

 outer portion : these are simply incurved portions of the whole 

 nasal wall (Fig. 162). 



The form of the true turbinal, which is usualh' supported by 

 cartilage — more rarely by bone, varies greatly. It is either repre- 

 sented by a moderate-sized prominence, or else it becomes more 

 or less rolled on itself The lachrymal duct opens below and an- 



