206 



DE. EMELETON AND ME. ATTHEY ON THE 



border of the jaw only by a narrow strip of the maxillary alveo- 

 lar border ; their external anterior angles have the large tusks, 

 hence called vomerine, implanted in them : behind each of these 

 is a large depression, each a little larger than the base of the 

 tusk, and resembling those of the premaxillary interdental spaces ; 

 and further back there is an aperture on each side in the jaw, 

 presently to be noticed. 



The outer borders of the vomers are next directed backwards 

 and inwards for about one inch and a half; thence they run 

 abruptly inwards and forwards, converging to the median line 

 of the palate. The angles they thus form together are inserted 

 between the palate-bones on the inner and the maxillaries on 

 the outer sides. 



The vomerine tusks present a clean fracture of circular outline, 

 with a diameter of seven-tenths by five-tenths of an inch. 



The apertures above noticed in the jaw are obscure ; they do 

 not pass through the jaw to its upper surface, but merely pierce 

 the nasal cavity. They are not in connexion with the anterior 

 nares. In Zepidosteus, a short way behind the snout, there is, 

 on each side of the median line, a complete perforation of the 

 maxilla for the reception of a mandibular tooth during closure 

 of the mouth. Perhaps the apertures in Loxomma have the same 

 use ; they are of about the same size as the depressions in front 

 of them, and are bounded internally and in front by the vomers, 

 externally by the alveolar borders of the maxillae, and posteriorly 

 by the anterior ends of the palate-plates of the same bones. 



The maxillaries are the longest bones of the skull, and consist 

 of alveolar borders and palate-plates. On the right side the al- 

 veolar border of the bone is very nearly perfect, whilst that on 

 the left side is nearly all wanting. The palate-plates are per- 

 fect on both sides. 



The alveolar border is a narrow tract of bone, eight inches and 

 a half long, extending from the premaxillary to the quadrate 

 jugal, with which latter it articulates at about three inches and 

 a half in front of the posterior end of the lateral part of the cra- 

 nium. The border which remains bears thirteen small teeth ir- 

 regularly disposed, and has four gaps from which both bone and 



