1.898.] OSTEOLOGY OF THE IMPE'N'T^^ES. 971 



In the two latter genera the anterior limb is wanting. In Pygo- 

 scelis (PI. LXI. fig. 3) the vertical height is relatively less ; the 

 anterior limb is wanting, as in Catarrhactes and Spheniscus ; the 

 posterior is of considerable length. The anterior and dorsal 

 borders, in Pyrioseelis, form a right angle ; the posterior is deeply- 

 hollowed, as seen in the figure. Between the free end of the 

 posterior limb and the epiotic is a wide space ; into the lower 

 portion of this the prootic has thrust it^self . The upper portion of 

 this space was originally filled in by cartilage and formed the outer 

 wall of the floccular fossa, as seen in the skull of a young Catar- 

 rhactes ; it is now filled up by an inward growth of the posterior 

 border of the parietal. Below the curved upper limb lies the 

 prootic, which runs backwards to join the exoccipital. The extreme 

 anterior end of the prootic is seen peeping out in front of the 

 supero-anterior squamosal border behind the alisphenoid. The 

 squamosal, at this stage, articulates wdth the parietal only and 

 rests upon the outer surface of the prootic. It is entirely shut 

 off from the cranial cavity. 



The epiotic (PI. LXI. fig. 3) is sharply divided from the supra- 

 occipital by a \^ide cleft rnnning downwards and inwards from the 

 lambdoidal suture, which terminates at about the middle region of 

 the epiotic in a groove — afterwards converted into a closed canal — 

 for one of the cerebral veins. This groove divides the lower end of 

 the epiotic, as does the cleft the upper end, from the supra-occipital. 

 Seen from without it is bounded mesially by the supra-occipital, 

 superiorly by the parietal, and laterally by the prootic and ex- 

 occipital. Its supero-lateral border is bounded by cartilage 

 (a synchondrosis) ; its postero-lateral border by a close suture. 

 Seen from within, the epiotic is found to be fused by its postero- 

 internal border with the supra-occipital, from which it is separated 

 above by the wide chink already described (p. 967). Its lateral 

 and external border is separated synchondrosially from the prootic 

 and lateral occipital. In conjunction with the prootic forms the 

 floccular fossa. 



The prootic is largely visible from without, till comparatively 

 late in life (PI. LXI. figs. 1 & 3). In the youngest skull from which 

 these descriptions are taken {Catarrhactes chrysocome), it can be seen 

 in the hinder region of the skull through a mass of cartilage 

 forming a small island, between the exoccipital, squamosal, 

 parietal, and epiotic. In the lateral view of the skull, after 

 removal of the quadrate, it can be seen lying between the ex- 

 occipital behind and the alisphenoid in front: below it rests on 

 the pretemporal wing of the hasisphenoid ; above it is covered by 

 the squamosal. After the removal of this, the boundaries of its 

 upper end can be clearly made out. It is found to be wedged in 

 between the alisphenoid and parietal above and in front, the ex- 

 occipital behind, and the epiotic mass of the supra-occipital within. 

 Its anterior border is deeply hollowed to form the posterior bo ""der 

 of the trigeminal foramen. Behind and above lies a glenoid cavity 

 for the quadraie. Its posterior border is also hollowed out to 



64* 



