173 



palatine bone. In front a portion is sent upwards inter- 

 nally at riglit-angles to the main portion and internally to 

 the palatine. This soon terminates, and the remainder of 

 the sac ends bluntly below the palatine. 



Postero-ventral nasal sac (n. sac.^). — Opens into the 

 nasal chamber as above described. It is very irregular in 

 shape, and three-rayed in transverse section. It passes 

 far backwards just above the mucous membrane and to the 

 right of the palatine, being narrow behind and ending 

 blindly just over the mucous membrane of the mouth 

 below and intoinal to the sclerotic of the right eye. 



Left Olfactory Organ. 



The anterior and posterior nostrils {a. nos.^ , j). nos.^) 

 are no diiferent from those of the right side, except that 

 the anterior tube is smaller and the posterior nostril is 

 larger and more widely open. 



The left nose is situated at a transverse level posterior 

 to that of the right, and is further much less developed. 

 This is most evident in the nasal chamber [n. ch.^), which 

 is obviously smaller and was in the sections only thrown 

 into 4 olfactory laminae (o. lam.^ ), the dorsal one of these 

 being quite small and the ventral one smaller than the 

 two intermediate laminae.* The figure does not admit of a 

 comparison as regards the nasal sacs, since their dimen- 

 sions from above downwards cannot be shown. 



There are only two nasal sacs on the left side as 

 follows : — 



Dorsal nasal sac (n. sac.*}. — Arises from the nasal 

 chamber dorsal ly from behind. At first its shape in trans- 

 verse section is that of an inverted right-angle — the verti- 



* The difference between the two olfactory organs is seen in the 

 diameter of the right and left olfactory nerves (fig. 25, n. olf., n. olf.'^). 

 The fio-ure only illustrates the difference in diameter, the difference in 

 bulk is even greater. 



