460 PROCEEDINGS OF THE ACADEMY OF [Julv, 



cells. On the right, the ventral nasal passage, v.])., is cut posterior to 

 its opening into the main nasal passage and is hence seen as an inde- 

 pendent, circular passage. On the left, the section passes through 

 the opening of the left ventral passage, v.p'., into its adjacent 

 main nasal passage. The ventro-lateral diverticula, d. and d'., are 

 seen on either side. The right side of the section passes through 

 the oi)ening of the cavity c. into the ventral part of the right nasal 

 passage, r.7i.c., while on the left the corresponding cavity, c'., is 

 cut anterior to its opening and is surrounded on all sides by the 

 nasal cartilage. In the preceding section the cavity c. Avas cut pos- 

 terior to the region at which it was completely surrounded by car- 

 tilage. 



In fig. 2h the nasal cartilages have about the same outline as in 

 the figure just described, the sections represented by these two 

 figures being close together. Jacobson's organ, j., has increased 

 somevv-hat in size, but there is still no trace of a cavity in either 

 part. Both ventral nasal tubes, v.p., are now entirely distinct 

 from the main nasal cavities and are somewhat circular tubes lined 

 with columnar cells. On the left the side cavity, c'., is still sur- 

 rounded by cartilage, being again cut anterior to its opening into 

 the left nasal passage, l.n.c, while on the right of the section, at 

 the point c. , the side cavity is seen to open dorsally into the main 

 nasal cavity. The relation of this side cavity to the main nasal 

 cavity is made plain by reference to fig. 3a, which represents a 

 section cut in the plane a-b, fig. lb. The section passed through 

 the dorsal part of the nasal cavities, cutting the cavity on the right 

 so far dorsally that but little indication of the side cavity, c, is 

 evident. It is plain, from this figure, that what ha« been called 

 a side cavity, c'., is merely the posterior end of the main nasal 

 cavity which has bent around until it projected outward and for- 

 ward, and thus gave the idea, in transverse section, of a distinct 

 ofishoot frorh the main nasal cavity, l.n.c. Fig. 3a shows how 

 the nasal cartilage, ».c., pushes in between the cavity c' and the 

 main cavity, l.n.c, giving the impression, in transverse section, 

 that the cavity c' is completely surrounded by cartilage. In a 

 section ventral to this one, what has been called the main nasal 

 cavity, l.n.c, is seen to extend somewhat further toward 

 the brain, br., and in that way the cavity c'. is made to appear 

 more like a branch of the main cavity than simply a forward 



