€36 MR. R. H. BUKNE ON THE ANATOMY OF THE [May 25, 



distance beyond the posterior nostril, and here are dilated above 

 and below the ridge that carries the olfactory nerve to the rosette 

 to form two large accessory sacs. The upper sac (ethmoidal) 

 bends forward beneath the ethmo-maxillary ligament parallel to 

 the npper margin of the olfactory chamber, and fills in all the 

 space available between the mesethmoid and the backward process 

 of the premaxilla. The lower (lachrymal) sac, after passing down 

 upon the lateral ethmoid, expands in the space between the 

 lachrymal bone, the palatine arcade and buccal membi-ane, and 

 the maxilla. 



It will be appai-ent from the close relations of these sacs to the 

 bones of the mouth that their expansion or contraction will depend 

 upon the movements of these bones. This is particularly the 

 case with regard to the ethmoidal sac, which is greatly expanded 

 as the premaxilla shoots forwai-d in the protrusion of the jaws 

 and compressed as it is retracted. The effect of the movements 

 of the maxilla upon the lachrymal sac is less apparent, although 

 the sac is visibly compressed by the hinder margin of this bone 

 as it swings back during the closure of the mouth. 



By forcibly closing the mouth under water it is possible to 

 cause the ejection of a stream of air-bubbles from both nostrils. 



The rosette is oval, slightly pigmented, and not veiy strongly 

 defined. Its laminae have the normal radial ai-rangement around 

 a linear raphe attached in front to the anterior wall of the 

 anterior nostril. The individual laminae (of which there are 

 about 30) are bluntly claw-shaped. 



Ophiocephalid^. 

 Ophiocephalus viat^ulms. 



The nostrils lie between the upper anterior border of the eye 

 and the snout in an area of soft skin between the nasal and 

 lachrymal scutes, separated from each other by a space equal to 

 the diameter of the eye. The anterior nostril is a simple per- 

 foration at the end of a tube overhanging the premaxilla, the 

 posterior a circular hole flush with the surface of the head close 

 in front of the frontal scute. 



The nasal cavity consists of two divisions, an olfactory chamber 

 proper occupying the anterior half of the space between the two 

 nostrils, and an accessory sac comprising the parts of the cavity 

 between the rosette and the posterior nostril, and extending 

 forward deep to the true olfactory chamber to the backward 

 process of the j)remaxilla. 



The rosette is quadrangular in shape and consists of a series of 

 laminae set parallel to one another in the longitudinal plane. 

 Each lamina (text-fig. 205, C) has a gently curved free margin 

 without linguiform process. The accessory sac is so closely applied 

 to a considerable part of the backward process of the premaxilla 

 that it necessarily shares in the movements of this bone, being 

 compressed when it is retracted, expanded when it protrudes. It 



