18 PROCEEDINGS OP THE ACADEMY OF [1889. 



cal plate of its outer boundary, while its inner wall is formed chiefly 

 by the lacrymal, and to a very small degree, posteriorly, by the 

 frontal. The jugal takes no part in its formation in Neotoma. 



Rodents are notorious for the large size of the premaxillary bones 

 in their skulls, and to this rule the genus now under consideration 

 forms no exception. Here a premaxillary of either side stands 

 between the corresponding nasal and maxillary, preventing those 

 elements of the face from coming in contact at any point. Supe- 

 riorly, it sends backwards a lanceolate-shaped apophysis to overlap 

 the frontal of the same side, and this feature is distinctly shown in 

 Plate I, Figs. 1 and 2. 



Laterally, it makes up the chief side-wall of the conical fore-part 

 of the skull of this embryo, and rounds under to form the roof of the 

 anterior part of the mouth, though here a mesially oval foramen 

 largely prevents it from suturally uniting with the fellow of the 

 opposite side down the middle line (Plate I, Fig. 3). Each one 

 anteriorly and beneath shows a diminutive pitlet, in which the inci- 

 sor tooth is budding out, the latter not quite tilling the hole closely, 

 and withal being yet in an elementary state. Either premaxillary 

 in the oval foramen above referred to, and on the outer aspect of the 

 nasal septum in front, send backwards a teat-like process, into the 

 spinal space ; and in the skull of the adult Neotoma, these processes 

 seem to have finally each pressed down upon the vomer and fused 

 with its infero-anterior part. A premaxillary articulates with a 

 nasal, a frontal, a lacrymal, the vomer, the ethmoidal mass, and with 

 the fellow of the opposite side, and at this stage it seems to have 

 progressed in its ossification, about as far as the nasals have, already 

 described above. 



The maxillary, on either side, is a very important, not to say inter- 

 esting, investing bone of the face and roof of the mouth (mx). It 

 sends backwards a delicate zygomatic process, which underlaps the 

 jugal to complete the zygoma. To some extent anteriorly, it con- 

 tributes to the formation of the bony walls of the orbit, especially 

 where it articulates with the lacrymal. In front, just beyond the 

 infra-orbital foramen, it articulates by a vertical suture with the 

 premaxillary of the same side, while behind this it sweeps down- 

 wards and inwards, to complete the posterior moiety of its own side 

 of the periphery of the incisor foramen, or " the anterior palatine 

 foramen " of Flower, after which it contributes to the osseous oral 

 roof, articulating by a transverse zigzag suture with the palatine, and 



