PLATANISTA. 525 



pterygoid is applied. The palatine process of the maxilla terminates posteriorly 

 in a hook and groove, the former embracing the palatine, and the latter receiving a 

 curved sharp ridge of the same hone. Behind this, looking backwards, is the rough 

 surface for the articulation of the palatine, above which is the small surface forming 

 the boundary of the anterior wall of the external nares, posterior to the premaxilla. 

 Above this is the expanded surface of the maxilla, which is applied to the frontal on 

 either side of its nasal ridge or crest. This surface, which is the highest portion of 

 the maxilla, looks backwards and downwards, and its extent varies on the two sides 

 of the skull owing to its sinistral twisting, the left being by far the smaller. The 

 right surface is concave in its lower two-thirds and convex above at its internal 

 extremity, where it rests in a deep concavity on the anterior surface of the frontal, 

 external to the nasal ridge. The frontal surface of the left maxilla is narrow and 

 wholly concave, the corresponding maxillary surface of the frontal being convex. 

 Anterior to the palatine surface of the maxilla and above the infra-orbital canal there 

 is a broad, but thin flat surface marked by numerous imperfections of ossification 

 in the young skull. This is defined above by a broadly arched free margin of the 

 external plate of the maxillary crest, the arch leading into the cavity that exists 

 between the two plates of the crests. This flattened surface is not applied to the 

 frontal, so that a large space exists between the two bones ; it is precluded from 

 communicating with the nasal cavities by the palatine and is closed below by the 

 pterygoids. Anteriorly it is continuous with the orbital cavity, so that the latter 

 communicates in the dry skull with the interspace between the plates of the maxil- 

 lary crests. Immediately above this arch, and below the whole length of the exposed 

 portion of the maxillary crests, there is an elongated, slightly convex surface, to 

 which the upper portion of the internal surface of the orbital process or wing of the 

 frontal is applied. There is a ridge running downwards and forwards from the pos- 

 terior angle of the crest to the posterior end of the free arched margin, leading into 

 the cavity of the crest, and the ridge defines the posterior limit of the application 

 of the orbital wing of the frontal to the maxilla, the surface of the maxilla poste- 

 rior to it looking backwards and its orbito-frontal surface outwards. It also defines 

 the posterior limits of the crest, and a line drawn from its lower extremity to the 

 orbital process, which projects forwards over the upper end of the interspace 

 (alveolar) between the plates of the maxilla, marks the lower limits of the maxillary 

 crest. An irregular ridge defines the base of the external portion of the crest 

 and corresponds to the upper free sharp wavy margin of the orbital wing of 

 the frontal. The external surface of the crest in young skulls is more or less 

 quadrangular, a form preserved in the adults, but becoming more constricted 

 posteriorly. At all ages, the superior posterior angle is rounded. In youth, an 

 external depression or constriction curves backwards, inwards and then forwards, 

 terminating immediately behind the superior anterior angle in a well-marked 

 depression ; but with age the external surface of the crest becomes nearly flat, 

 and the constriction is reduced to a depression at the base of the crest about its 

 middle. In young skulls a number of fine grooves radiate inwards in a curved 



