196 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



turbinals and the maxillo-turbinals (fig. 200), the purpose of these 

 folds being to increase the amount of sensory surface, while the skeletal 

 supports keep the folds from touching each other. With diminution 

 of the powers of smell the folds are correspondingly reduced, even to 

 a loss of the turbination 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 

 insinuate itself between the hinder ends of the 

 other two (figs. 200, 201). Each of these may be 

 subdivided, with corresponding subdivision of 

 the epithelial covering, and in the case of the 

 ethmo-turbinals the subdivisions may be of 

 varying heights (fig. 202), the ecto- and ento- 

 turbinals. The nasoturbinals often disappear in 

 through the nasal cavity the adult, while the epithelium of the maxillo- 



ofia new born dog, after , . , , ,. . 



Paulli, I-IV, entoturbi- 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 dif- 

 ferent amniotes are thus stated (Peter) . 



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



II. Conchae of the primitive sensory epithelium : 



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



A. Anterior: 



a. Primary, ventral: concha of reptiles; middle concha 

 of birds; maxillo-turbinals of mammals. 



b. 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. 

 Jacobson's organ (vomero-nasal organ) is laid down in the embryo 

 of most mammals as a groove or pocket on the lower medial side of 

 each nasal cavity, opening in rodents and in man near the duct of 



FIG. 202. Section 



nals; 1-5, first to fifth ec- 

 toturbinals. 



