16 ILLINOIS BIOLOGICAL MONOGRAPHS [186 



end of the brain case is located between the ventral flanges of the 

 frontals. 



Facial Bones 



PremaxUlary. — The premaxillary (Fig 9) is a long curved 

 bone bearing teeth. Its anterior end is thickened and bears two dorsal 

 processes extending dorso-caudad, with a V-shaped slit between them. 

 The anterior process is long, slender, and laterally flattened at the base 

 and gradually becomes rounded distally until at its end, where it articu- 

 lates with the ethmoid, it is antero-posteriorly flattened. The posterior 

 process is broad and thick at the base and as it nears the end it makes 

 a sharp curve and comes to a point at its anterior edge ; on its anterior 

 mesial surface it has a deep depression into which an angular process 

 of the maxilla passes as it articulates with that bone. It is rounded on 

 its dorso-lateral surface except at a point slightly posterior to the middle 

 where it has broadened and flattened into a sharp edge ; from this point 

 it gradually tapers to a long slender point which extends on the lateral 

 surface of the mandible. The anterior end of the bone, anterior to the 

 processes, is rounded and thickened as it nears the median line where 

 it unites with its fellow from the opposite side. Two kinds of teeth 

 are present on the premaxillary, an inner row of canine-shaped teeth 

 and from one to several irregular rows of the villiform type. 



Maxillary. — The maxillary is a long curved bone without teeth, 

 having a thick articular head and a flat expanded hind end. The former 

 has a large articular facet which appears double on account of a V 

 between its articular surfaces. The antero-mesial of these processes 

 curves mesad and lies inside of the dorsal process of the premaxillary 

 with which it articulates, directly dorsal to the dorsal limb of the vomer. 

 The antero-lateral process is drawn out into a pointed projection lateral 

 to the process of the premaxillary with which the other process articu- 

 lates, and upon which the anterior ends of the nasal and palatine bones 

 rest. At the apex of the V between the articular processes, the bone 

 is rounded mesad at the point where it fits over the process of the pre- 

 maxillary. The ventral edge of the first suborbital rests on the dorsal 

 surface of the maxilla for some distance back from the anterior end. 

 The posterior flattened and broadened end rests on the lateral edge of 

 the mandible as it passes postero-ventrally from the anterior end. 



Nasal. — The nasal is a small bone connecting the prefrontal, 

 ethmoid, and the maxilla and forming the roof of the nasal pit. It is 

 Y-shaped, with one edge of the broad end lying on a small process on 

 the dorso-anterior edge of the prefrontal and the other on the antero- 

 lateral process of the ethmoid. The pedicle extends cephalad and rests 

 upon the maxilla, thus forming the roof of the nasal pit. 



