740 B. W. KITNKEL 



PALATOQUADRATTOl AND MANDIBLE 



The palatoquadratum of Emys is of special interest since it 

 has a distinct pars palatina, or processus pterygoideus ; a condi- 

 tion which recalls the primitive one of the skull of Sphenodon and 

 the Anamnia in general. It is entirely disconnected from the 

 rest of the skull. The pars quadrata lies close alongside of the 

 lateral wall of the otic capsule and the pars palatina alongside of 

 the crista basipteiygoidea , both parts, however, are separated 

 from the median portion of the skull by at least a thin layer of 

 non-cartilaginous tissue. The form of the pars quadrata has 

 been very aptly compared to that of the external ear of man with 

 the convex margin du-ected anteriorly and the concave margin 

 posteriorly; accordingly the anterior portion of the pars quadrata 

 is much liigher dorso-ventrally than the posterior portion. It is 

 of about the same size as the otic capsule so that it conceals the 

 latter somewhat when viewed from the side. Its ventral portion, 

 the pars articularis, Ues well below the level of the basal plate so 

 that its dorsal margin lies also somewhat below that of the otic 

 capsule. In its posterior portion, the pars quadrata, fits into the 

 broad, shallow groove formed on the lateral wall of the otic 

 capsule by the crista parotica and the portion of the prominentia 

 canalis semicircularis lateralis which lies dorsal to it. The median 

 wall of the pars quadrata has a nearly vertical position so that it 

 is much further removed from the capsule ventrally than dorsally 

 where the lateral semicircular canal projects. In the compara- 

 tively narrow space between the quadratum and the otic capsule 

 are situated the arteria carotis interna and vena capitis lateralis 

 which extend, parallel to each other, obliquely from postero-ven- 

 tral to antero-dorsal, as has already been described by Noack. 



The pars quadrata may be differentiated into two distinct 

 portions, a postero-dorsal one wliich encloses an extension of the 

 tympanic cavity, regarded by Hasse as the homologue of the 

 antrum mastoideum of human anatomy (pars mastoidea), and 

 an antero-ventral portion which lacks the outer wall of the former 

 and so exhibits an imperfect cup shape (pars articularis). The 

 pars mastoidea of the quadratum forms a hollow cone, flattened 

 from side to side, with its apex directed posteriorly and its base 



