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- 
Fic. 202--Section trbinals. The nasoturbinals often disappear in 
through the nasal cavity the adult, while the epithelium of the maxillo- 
er pt ey turbinals is not sensory in character, this part 
eo Ob Ae nese 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. Conche of the primitive sensory epithelium: 
1. Arising from the lateral wall (conche laterales). 
A. Anterior: Be a 
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: conche obtecte 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 
