OLFACTORY ORGAN. 175 



extends further and further backwards, in 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. 



In Crocodiles, as in other Reptiles, there is only a single true 

 turbinal, but externally to it lies a second prominence, which 

 is spoken ofasapseudo-turbinal. 1 Each nasal chamber of the 

 Crocodile is divided posteriorly into two superimposed cavities, the 

 upper of which represents the proper olfactory chamber, and is 

 lined by sensory epithelium, while the lower functions as a 

 respiratory portion only. Certain accessory chambers are con- 

 nected with the nasal cavity, which, however, serve only as air- 

 chambers. A large gland, similar to that of Lizards and Snakes, 

 lies in the cavity of the upper jaw, and opens into the nasal 

 cavity. 



Birds. In all Birds, as in Lizards, there is an outer chamber, 

 lined by stratified epithelium, and a proper olfactory chamber, 

 which lies above the former. Birds also possess only a single 



FIG. 146. TRANSVERSE SECTION THROUGH THE RIGHT NASAL CAVITY OF A 

 SHRIKE (Lanius minor). 



OM, MM, superior (pseudo) and middle (true) turbinal ; a, upper, and b, lower nasal 

 passage ; LR, air-chamber, which extends into a hollow of the superior turbinal. 



true turbinal, if by this term is understood a free independent 

 projection into the nasal cavity supported by skeletal parts. Two 

 other prominences (pseudo-turbinals) are, however, present, one of 

 which 2 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. 146, MM, OM). 



The form of the true turbinal, which is usually supported 

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

 represented by a moderate-sized prominence, or else it becomes 

 more or less rolled on itself (forming as many as three turns). 

 The lacrymal duct opens below and anteriorly to it. There 



1 The meaning of the pseudo-turbirial will be discussed in the description of the 

 olfactory organ of Birds. 



2 Its cavity communicates with an air-sinus lying in the anterior orbital space. 



