302 Hen- F. Siebenrock on the. 



2 plciiroccipitals, and 2 paroccipitals. On account of tlil.s 

 remarkable fact Ilatteria approaches the Chelonians and 

 recedes further from tlic Lacertilians. 



It may not be witliout interest to give a separate represen- 

 tation and description of the individual bones of the cranium 

 of Ilatteria^ specially with a view to the acquisition of a 

 more precise knowledge of the bony auditory structures con- 

 tained within them. Giinther {loc. cit.) did not figure the 

 cranium or its individual bones, and Briihl, although he gave 

 a representation of the cranium from below and behind, paid 

 less attention to the auditory apparatus than to the demon- 

 stration of the absence of a paroccipital as alleged to exist by 

 Giinther. 



The basioccipital is an almost quadrangular and somewhat 

 bulky bone. Jts upper surface is concave, while its under 

 convex surface is swollen at the two lateral margins and Avith 

 the basisphcnoid forms the two very powerfully developed 

 tubercula sphenooccipitalia. These are always characterized 

 by an epiphysis. 



Behind the tubercula sphenooccipitalia lies the very large 

 pars condyloidea, which forms the posterior border of the 

 basioccipital, at the two angles of which are situated the 

 points of attachment for the pleuroccipitals. The anterior 

 border is almost straight ; it serves to unite the bone with the 

 basisphcnoid, which, with its two posterior processes, which 

 are separated by a triangular notch, lies upon the under 

 surface of the basioccipital and reaches to the tubercula 

 sphenooccipitalia. In this manner there arises in relief upon 

 the under surface of the basiocci])ital a triangular protuberance. 

 The two lateral borders of the basioccipital unite posteriorly 

 at the pars condyloidea with the pleuroccijiitals, in the middle 

 and anteriorly with the paroccipital and the otosphenoid. 

 Each lateral border of the basioccipital exhibits indeed in 

 front of the pars condyloidea a somewhat deep indentation, 

 the incisura vena3 jugularis, which, with a similar indentation 

 constituted by the ])ar(ieei)ntal and plcuroccipital, is completed 

 to form the ioranien jugulare. In iVont of this incisura venaj 

 jugularis the lateral border towards the anterior angle is 

 transformed into a deep ]ut, the posterior margin of which 

 unites with the paroccipital and the anterior witii the basi- 

 sphcnoid, while its outer and inner margins serve to su|>port 

 the membranes which till uj) the space between the three 

 bones already mentioned and the otosphenoid. This pit 

 closes the bony cochlea below. It was shown by me that it 

 also occurs in JJiookesia .snjurciliaris*^ where I designated 

 it the fossa cochlearis. It has an oblique situation in a 



* ¥. Siebenrock, "I'ns Sijelet vou Brookesia siipercilian'K, Kiihl," 



