OLFACTORY ORGANS. 1g5 
There are three folds developed on the wall of each nasal cavity in 
birds, an anterior and inferior concha vestibuli, a middle and a superior 
fold, the middle supported by the maxillo-turbinal, the superior by the 
naso-turbinal bones. The vestibular conch lacks olfactory epithelium 
at all times, while it disappears from the middle one after hatching, 
Fic. 199.—Olfactory region of hen in longitudinal and transverse section, after Gegen- 
baur. c, middle concha; ch, choana; 7, inferior (anterior) concha; 0, connection of air 
cavity of head; p, septum of nose; s, superior concha. 
leaving the upper conch as the sole seat of smell in the adult, which 
corresponds with the limited sense of smell in these animals. Jacob- 
son’s organ is never developed in the adult, though traces of it appear 
in the embryos. 
With the great increase of the sense of smell in the mammals the 
FIG. 200. Fic, 201. 
Fic. 200.—Model of the nasal cavity of a rabbit embryo, 134 mm. head length, after 
Peter. ch, choana; ét, first ethmoturbinal; 7, organ of Jacobson; 0j, opening of same; mt, 
maxilloturbinal; 2, nasoturbinal. 
Fic. 201.—Nasal cavity of Erinaceus, after Paulli, showing the foldings of the maxillo- 
turbinals (m#) and the nasoturbinals (nt). : 
nasal labyrinth undergoes a corresponding complication, and is 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 com- 
plicated, of three bones or cartilages, the ethmo-turbinals, the naso- 
