OLFACTORY ORGANS 



211 



farther characterized by the great length of the naso-pharyngeal duct, 

 and by the position of the olfactory area below a part of the brain 

 cavity. The folds of the labyrinth may be supported by processes, 

 more or less complicated, of three bones or cartilages; the ethmo- 

 turbinals, the naso-turbinals and the maxillo-turbinals (fig. 224), 

 the purpose of these folds being to increase the amount of sensory sur- 

 face, while the skeletal supports keep the folds from touching each 

 other. With diminution of the powers of smell the folds are cor- 

 respondingly reduced, even to a loss of the turbina- 

 tion of the bones concerned. 



The maxillo-turbinals and naso-turbinals arise 

 from the lateral wall of the nasal cavity (the 

 former as a distinct turbinal bone), the ethmo- 

 turbinals as outgrowths from the ethmoid bone, 

 appearing first at the upper hinder part of the 

 septal wall and extending to the lateral wall. The 

 result is that the ethmo-turbinal tends to insin- 

 uate itself between the hinder ends of the other 

 . fr NT-'T-r^T- 1-1- Fig. 226. — Section 



two (figs. 224, 225). Each of these may be sub- through the nasal cavity 



divided, with corresponding subdivision of the ?f M^.^T^r°rr° ^°^' ^^1" 



. ^ ° Paulli, I-IV, entoturbi- 



epithelial covermg, and in the case of the ethmo- nals; 1-5, first to fifth 

 turbinals the subdivisions may be of varying ectoturbinals. 

 heights (fig. 226), the ecto- and entoturbinals. The naso-turbinals 

 often disappear in the adult, while the epithelium of the maxillo- 

 turbinals is not sensory in character, this part of the nose being 

 apparently to warm and moisten the air in its passage to the lungs. 

 The homologies of the various parts of the nasal labyrinth in 

 different amniotes are thus stated (Peter). 



I. Concha of the anterior epithelium: concha vestibuli (birds). 



II. Conchae of the primitive sensory epithelium: 



I. Arising from the lateral wall (conchae laterales). 



A. Anterior: 



(a) Primary, ventral: concha of reptiles; middle concha 

 of birds; maxillo-turbinals of mammals. 



{h) Secondary, dorsal: Upper or posterior of birds; naso- 

 turbinals of mammals (? pseudoconch of crocodiles). 



B. Arising from the posterior part: conchae obtectae of mam- 



mals. 

 2. Arising from the primitively median wall: ethmo-turbinals 

 of mammals, numbered from in front backward. 



