PAL^OMASTODON. 137 



interrupted opposite the front lobe of the last molars by a pair of elongated apertures, 

 the posterior palatine foramina {p-P-f-). The upper edge of the palatine seems to 

 extend up into the side of the skull above the maxilla, where it joins the lower edge of 

 the orbitosphenoid. 



The vomer (text-fig. 49, v.), as already remarked, extends backwards considerably 

 behind the level of the posterior border of the hard palate and forms a long V-shaped 

 crest along the roof of the nasal canal. 



In this specimen the upper portion of the maxilla {mx.) is broken away in front, so 

 that its relations in that direction cannot be determined. The alveolar region is very 

 long and almost straight, there being only a very slight outward convexity ; it bears 

 six ch,eek-teeth (three premolars and three molars). The base of the zygomatic 

 process is long and nearly parallel with the alveolar border, from which it is separated 

 by an interval of about 3 cm. : the anterior end is about opposite the front of m. 3. 

 The upper surface is concave and forms the lower border and floor of the orbit. 

 Anteriorly it is perforated by the antorbital foramen, which, judging from the young 

 skull described below, had two openings on the face — a lower larger one preserved 

 in the present specimen, and a smaller upper one here broken away. The much 

 smaller size of the antorbital foramen in Palceomastodon compared with that seen in 

 Mephas, is no doubt due to the fact that in the older form the proboscis was still 

 comparatively small. 



Behind the orbit there is a small upwardly directed process of the zygoma, 

 marking the anterior limit of the jugal, which sends forwards a long process 

 overlapping the maxilla and helping to bound the orbit. The form of the suture 

 between the jugal {ju.) and the maxilla {mx.) will be best understood by examination 

 of the figure (PI. XII. fig. 1). The palatine plates of the maxilla are rather narrow 

 and together form a palate which is gently arched from side to side ; posteriorly they 

 are separated by the palatines as above described. Behind the last molar the bone 

 is greatly thickened by sinuses, so that, although the dentition is still of a perfectly 

 normal type, the increase in the size of the hinder part of the maxilla, which is 

 carried to such an enormous extent in the later forms, in which the teeth are 

 greatly enlarged, has already begun to manifest itself. Superiorly the bone appears 

 to unite with the orbitosphenoid in a straight suture running forwards and downwards. 

 The anterior portion of the orbital region is wanting. The maxilla, as might be 

 expected from the character of the dentition, dilFers widely from that seen in 

 the Elephants. The chief differences are : (1) the much greater relative length 

 of the bone ; (2) its smaller depth consequent upon the brachyodont character of 

 the teeth. These features are especially noticeable posteriorly, where, except for the 

 development of the sinuses in the bone behind m. 3, there is no trace of the enormous 

 increase in size in all dimensions, but especially in depth, which has taken place in 

 Mephas in consequence of the immense size of the posterior molars and their mode of 



T 



