98 



ALUS. [Vol. XVIII. 



The Parietal {PA) is an irregular and somewhat oval bone, 

 on the dorsal surface of which there is a tall, thin ridge. This 

 ridge, which projects backward behind the body of the bone, forms 

 the middle part of the bony ridge that separates the temporal and 

 supratemporal grooves. The mesial edge of the bone overlaps 

 slightly the lateral edge of the supraoccipital. Its anterior edge 

 connects with the hind edge of the frontal, partly overlapping and 

 being partly overlapped by it. Its lateral edge overlaps consider- 

 ably, and lies upon, the dorsal surface of the postorbital ossifica- 

 tion, connecting there with the mesial edge of one of the posterior 

 processes of the frontal, and with the mesial edge of the anterior 

 part of the dorsal process of the squamosal. The mesial part of its 

 hind edge overlaps and rests upon the exoccipitale. The lateral 

 part of its hind edge turns downward over the ledge that separ- 

 ates the anterior and posterior portions of the temporal groove, 

 and there overlaps, in part by delicate processes, the squamosal, 

 the exoccipitale, and the small temporal interspace of cartilage. 

 The body of the parietal rests upon cartilage in a small part only 

 of its extent, the larger part of the ventral surface of the bone 

 taking direct part in the formation of the roof of the cranial cavity. 



The Exoccipitale (£0) is a somewhat conical bone, the point 

 of which forms a pronounced process on the dorsal edge of the 

 hind end of the skull, lying about midway between the posterior 

 process of the squamosal and the spina occipitalis. The bone has 

 dorsal, lateral and posterior surfaces, the dorsal surface being 

 separated from the other two by sharp edges, and the other two 

 separated from each other by a strong rounded edge. The bone 

 adjoins the supraoccipital mesially and antero-mesially, the squa- 

 mosal ventro-laterally, and the occipitale laterale ventro-poster- 

 iorly. The mesial edge of its posterior surface almost touches 

 the corresponding edge of the bone of the opposite side of the 

 head, the adjoining edges of the two bones there being overlapped, 

 externally, by the postero-inferior portion of the supraoccipital. 

 The anterior corner of the bone bounds the posterior edge of the 

 temporal interspace of cartilage, and is overlapped, for about one 

 third the length of the bone, by the hind end of the parietal. 



The dorso-posterior point or summit of the exoccipitale is di- 

 rected dorsally, laterally and posteriorly, and is prolonged into a 



