NATURAL SCIENCES OF PHILADELPHIA. 315 



of thread-like tenuity, with the fore end slightly elbowed and 

 sharpened to lie by oblique suture against the maxillary, on the 

 inner side, and the hind end slightly clubbed to suture by a 

 roughened flat surface with the heel of the squamosal ; and such 

 are the relations of the parts, that the malar seems to run against 

 the otic capsule. The depressed position of this bone, which lies 

 down on the level of the palate, has been already noticed. 



The maxillary bone, with a general shape and connections 

 which scarcely require notice, has two peculiarities ; one of these 

 is the singular position of the "ante-orbital" foramen; here a 

 large circular perforation at the anterior border of the side of the 

 bone, altogether remote from the orbit. It lies above and even in 

 advance of the incisive foramina. Its fellow is only separated by 

 the width of the compressed muzzle ; there is a thin partition, 

 probably ethmoidal, between them. The other peculiarity of the 

 mastoid is the unusually extended and vaulted zygomatic plate, 

 which thus roofs over a considerable part of the orbit. This in- 

 flated lamina suddenly comes to a point where the malar joins it. 

 Its suture with the frontal, or the surface of the skull, is a 

 straight line. 



The incisive foramina, in Geomyidw, are wholly in the inter- 

 maxillaries ; in Dipodomys they are formed by both bones, the 

 maxillaries bounding about a third of their periphery. The 

 nasal spur of the intermaxillary extends upon the forehead a 

 little way beyond the ends of the nasals ; while a sharp process of 

 the frontal separates it from the maxillary. The alveolar 

 portion is remarkably curved backward, to suit the trend of the 

 incisors, and a strong alveolar plate separates the teeth for about 

 half their length. 



The nasals are chiefly notable for their length and tenuity ; they 

 reach far beyond the incisors ; the back half is linear and super- 

 ficial ; anterior to this, where the intermaxillaries bend down, 

 they become somewhat volute, prolonging a semi-tubular snout. 

 Within, delicate turbinal scrolls are seen extending to the orifice. 

 The nasals are supported, nearly to their ends, by small inter- 

 maxillary spurs. 



The mandible remains for consideration. This bone is remark- 

 ably small, considering the size of the rest of the skull, and is 

 further notable for its slight elevation posteriorly, its short 

 incompleted symphysis, and the thickness of the body of the 



