292 



THE AMERICAN NATURALIST 



[Vol. XL 



a greater surface than any bone in the skull Seen from the dor- 

 sal aspect, it is nearly rectangular in outline, but seen from the 

 ventral side, it exhibits a long, postero-laterally projecting process 

 which underlies the squamosal and quadrate bones. Its anterior 

 and lateral borders are thin, and the former makes the irregular 

 oudine of the posterior border of the orbit. The antero-lateral 

 corner is connected with the maxillary by a band of connective 

 tissue, as has already been pointed out. The median border 

 underlies the ethmoid to a slight extent, and is attached ventrally 

 to the side of the parasphenoid. The posterior border is hid- 

 den, in a dorsal view, by the squamosal and quadrate, with which 

 it articulates. The above-mentioned postero-laterally projecting 

 process of the pterygoid is an elongation of the lateral and posterior 

 borders, and extends entirely across the squamosal until it shows 

 behind it, and forms a part of the articular surface for the lower 

 jaw. This projection of the pterygoid behind the squamosal 

 and quadrate is shown in Fig. 1. The pterygoid is somewhat 

 arched from side to side, with the convexity of the arch dorsad. 

 Above the postero-median corner of the pterygoid, in the angle 

 between the ethmoid, the parietal, and the squamous, is a marked 

 depression (see Fig. 1 ) covered in life by a membrane. In the 

 bottom of tliis depression several canals leading into the cranial 

 cavity may be seen. One of these canals is much lar<:('r titan the 

 others, and is said by Osawa to be for the exit of the trigeminal 

 nerve. At the ]K>stero-lateral corner of the depression is a short 

 canal, formed by a narrow space left between the squamosal above 

 and the pterygoid below. This canal does not lead into the cavity 

 of the skull, but extends backward to the outer side of the auditory 

 capsule, and seems to be an anterior continuation of the vertebral 

 canal ; it is api)ai-ently the canal that Osawa calls the palatine. 



The .sijiitnnoKs bones (S.) are among the most important in 

 determining the shape of the skull. They are elongated, rod- 

 shaped bones that extend laterally, at fight angles to the long 

 axis of the skull, and form the sqi.are outline of it> ba..". Kach 



medial end of the boiie is somewhat ihiUenn! an.l enlarovd. and 



