632 



MR. R. H. BURNE ON THE ANATOMY OF THE [May 25, 



the maxilla is comparatively fixed, its lower end forming the fulcrum 

 upon which the premaxilla swings backwards and forwards. 



Orestias lesueuri. 



In this species the olfactory organ is of the same type as in 

 Anahleps, though differing from it in detail. The anterior nostril 

 is not tubular but is a simple hole, minute and easily overlooked, 

 lying near the anterior margin of the maxilla towards its upper 

 extremity. The posterior nostril on the other hand (text-fig. 201 , A) 

 is a large oblique slit in front of and above the eye and is bordered 

 posteriorly by a valvular flap, which is separated from the parts 

 behind it by so deep a gutter that at first sight it might be taken 

 to be the posterior nostril, and the true nostril mistaken for the 

 anterior, simixlating such a pair of closely applied nostrils as those 

 of the Herrings. The nasal cavity is essentially similar to that of 

 Anahleps, but the accessory sac is not so large and passes inwards 

 around the posterior border of the maxillary process of the palatine 

 and not forwards towards the premaxilla. 



Text-fis. 201. 



Orestias lesueuri. 



A. The nostrils in their relation to the superficial bones of the face. 



B. The form and position of the olfactory cavity. 



L., ligament between the ethmoid and palatine. 



Movements of the jaws had but little effect apparently upon 

 the contents of the nose-cavity, but when the opei-culum was 

 raised and lowered air-bubbles could readily be expelled from the 

 posterior nostril. This effect seems to be due to the movements 

 of the maxillary process of the palatine. This bone is attached in 

 front in the usual way (though loosely) to the maxilla and at the 

 root of its maxillary process by a long ligament to the lateral 

 ethmoid. As the gill-cover is opened the maxillary process of the 

 palatine rotates inwards and backwards around this ligament as a 



