DEVELOPMENT OF THE SKULL OF EMYS 719 



TECTUM POSTERIUS 



The tectum posterius, which is the only part of the chondrocra- 

 nium roofing in the central nervous system dorsally, is continuous 

 ventro-laterally with the otic capsules, and so may properly be 

 described with the otic region notwithstanding the fact that it 

 extends posteriorly to close in the foramen occipitale magnum 

 above. The tectum posterius may be differentiated into a me- 

 dian and two lateral portions. The latter are slender cylindrical 

 rods which slant medially and dorsally from the upper margin 

 of the otic capsule in order to support with their distal median 

 ends the large median portion which is of rhomboidal form with 

 its long axis in the sagittal plane. This median portion accord- 

 ingly exhibits a long, slender triangular processus ascendens which 

 slants upward in an anterior direction and a stouter processus 

 posterior which is more nearly semicircular in form and extends 

 with its postero-ventral extremity to limit the foramen occipitale 

 magnum above. In cross section the processus ascendens be- 

 comes crescentic toward its apex, with the convexity directed 

 dorsally, while that of the processus posterior is more nearly 

 oval. The tectum is slightly curved in the sagittal plane, thus 

 exhibiting a postero-dorsal convexity and an antero-ventral 

 concavity. The saccus endolymphaticus is situated close below 

 and in front of the slender lateral portion. 



CRISTA PAROTICA 



The crista parotica {cr.p., fig. 28) forms a short, longitudinal 

 crest, extending in an anterior direction from the ventro-lateral 

 aspect of the prominentia ampuUaris posterior slightly beyond 

 the foramen glossopharyngei externum, dorsal to which it ends 

 freely in a vertical, transverse face {cr.p., fig. 2). It is triangular 

 in cross section exliibiting a ventral and a median surface, the 

 latter attached to the otic capsule except at its extreme anterior 

 end which projects freely. There is accordingly a dorso-lateral 

 face which makes a broad, shallow groove with the part of the 

 external wall of the otic capsule lying dorsal to it in which the 

 postero-ventral portion of the quadratum rests. 



