27 



panding' to form the head, which is capped with cartilage. 

 The head has 4 articulations : (1) It is closely attached 

 above to the large unpaired intermaxillary oartilagej 

 (I.M.C.), to which on its other side the left maxilla is also 

 attached ; (2) ventrally the maxilla is capped by a move- 

 able piece of cartilage, much smaller and situated ventral 

 to the inter-maxillary. This moveable or gliding car- 

 tilage! works in the groove to the right of the beak-like 

 mesethmoid prominence (cp. fig. 1), and also over the 

 large convex facet on the right side of the head of the 

 vomer. It is connected with the inter-maxillary and is 

 excavated on both surfaces to receive the head of the 

 maxilla and the vomerine facet. The latter or free exca- 

 vation is so contrived as not to interfere with the move- 

 ment of the cartilage above the vomer. The reader who 

 consults a dried cranium of the Plaice when reading this 

 description will understand that the movement permitted 

 to the maxillary bones by these facets and gliding car- 

 tilage is an oblique dorse-ventral one in the direction of 

 the eyeless side (cp. Traquair oj). cit.). This explains the 

 well-known fact that Plaice are able to pick up food lying 

 on the sea bottom by twisting the mouth towards the lower 

 or eyeless side. In other Pleiironectidre the twisting of 

 the mouth is towards the ocular side ; (-5) dorso-posteriorly 

 the maxilla, as already pointed out, is connected by liga- 

 ment with the anterior extremity of the palatine ; (4) 

 anteriorly and externally it is deeply excavated for the 

 reception of the pre-maxilla. The anterior edge of the 

 maxilla is close to and partly overlaps the pre-maxilla. 



Pre-Maxilla (P.il/.r.).— Forms the dorsal part of the 



gape and consists of two arms. Its vertical arm forms the 



gape and bore 4 teeth in the specimen now described, 



I We follow Traquair in using this term for the cartilage in question. 



t Cp. Traquair, Trans. Linnean Soc, London, xxv., 1865. 



