1901.] NATURAL SCIENCES OF PIIILADELrHIA. 461 



bendiug of the larger cavity. This posterior extension of the 

 main nasal cavity is shown in fig. 21, l.n.c. Fig. 3a shows that 

 the median nasal cartilage, s., extends back between the eyes, and 

 becomes continuous with the cartilage surrounding the brain. It 

 is somewhat swollen at a point about half-way between the nasal 

 cavities and the brain. 



The section repi*esented in fig. 21 passes through the extreme 

 posterior part of the main nasal cavities, l.n.c. and r.n.c, and 

 cuts the ventral canals, v. p., posterior to the point at which Jacob- 

 son's organ opens into them. The way in which this takes place 

 will be described later. The lateral parts, n.e., of the nasal carti- 

 lages have diminished considerably in size, and now lie much 

 nearer to the median cartilage, s. This section passes through the 

 anterior ends of the two olfactory lobes, o. I. 



In fig. 2/ is represented a section cut posterior to the nasal 

 cavity, so that neither of the main or dorsal nasal chambers are 

 seen. The ventral passages, v.jj., have about the same size and 

 position as In the preceding figure, while the lateral cartilages, 

 n.e., are reduced to mere rods, lying close against but not fused 

 with the median cartilage, 6\ A short distance posterior to this 

 point these cartilages end. 



The section seen in fig. 2k is some distance posterior to the one 

 just described, and shows how the ventral canals, v.j)., unite to 

 form a single median canal, before they open posteriorly as the 

 posterior nares. 



This section does not cut the lateral parts of the nasal cartilage, 

 but the median septum, s. , is seen extending dorsally, b.c, on 

 ei-ther side of the olfactory lobes, o.l. The outlines of the muscles 

 of the eyes are shown in this as well as in the following figure by 

 dotted lines, m. 



Fig. 2ns somewhat posterior to fig. 2k, and passes through the 

 opening of the ventral passages, the jioscerior nares, p.n. The 

 other points brought out in this figure are about the same as in 

 fig. 2k, and need no further description. 



Fig. 4a represents, under a much higher magnification, a part 

 of one of the sections of the series that has just been described. 

 The veuti-al end of the median cartilaginous septum is shown at s., 

 and the ventral ends of the right and left nasal passages are seen 

 at r.n.c and l.n.c. The walls of these passages are made up of 



