ANATOMY OF THE BEAVER. 57 



letter V, is formed by them. The frontal bone is 

 flattened above. The two bones are early united, 

 and in the adult present only the trace of a suture. 

 The frontal is broadest anteriorly, spreading out to 

 form the anterior orbital processes. From a rounded 

 margin the orbital plate descends nearly vertically 

 into the socket. This margin is a little prominent 

 posteriorly, forming a smaller process. From this 

 point the bone is wedge-form, passing backward 

 between the parietals. In the orbital cavity the 

 frontal joins the lachrymal, the superior maxillary 

 and the ala of the pre-sphenoid. The lachrymal is 

 triangular above, wedged in between the frontal and 

 malar; it forms part of the inner anterior portion of 

 the orbit. The parietal bones are about half the 

 length of the skull. They are united in their middle 

 third by suture, being separated anteriorly by the 

 frontal bone, and behind by the interparietal; they 

 extend back to the occipital and join the temporals 

 by a longitudinal suture. Their anterior margin in 

 the temporal fossae is inflected, roughened, forming a 

 crest which extends on the temporal to the zygomatic 

 process; in the fossee they join the alae of both sphe- 

 noids; posteriorly and laterally their pointed extremi- 

 ties extend a short distance behind the temporals. 

 The interparietal bone is triangular, but very variable 

 in its form in different skulls. In young subjects it is 

 in two portions, divided by the sagittal suture; in old 

 skulls the place of the suture is occupied by a sharp 

 crest. The base of this bone joins the occipital. The 

 temporal bones are lateral. The zj^gomatic process 

 extends downward and outward, in a flattened form, 

 to constitute the roof of the glenoid cavity; then 



