DEVELOPMENT OF THE SKULL OF EMYS 703 



rods which recall strikingly the neural arches of the vertebrae. 

 Their medial margins are curved regularly to enclose the foramen 

 occipitale magnum laterally; their external margins, however, 

 exhibit a more angular contour because of a marked thickening 

 midway between their base and apex against which the otic cap- 

 sule rests posteriorly. The fissura metotica is accordingly greatly 

 narrowed here but not completely obliterated. The arcus occipi- 

 tales bound the foramen occipitale magnum laterally and the 

 fissura metotica posteriorly and niedially. 



The foramen occipitale magnum is large and of hexagonal form, 

 with its dorsal and ventral margins transverse and with lateral 

 angles. Its plane is vertical and transverse. The condyle and 

 basal plate form its ventral margin, the curving arcus occipitales 

 its lateral margins, and the free posterior margin of the processus 

 posterior of the tectum posterius its dorsal margin. 



REGIO OTICA 



In contrast to the occipital the otic region is complicated. The . 

 basal plate forms the floor, the otic capsules the lateral walls and 

 the tectum posterius the dorsal portion. Of the basal plate 

 there should be mentioned the large, hexagonal fenestra basi- 

 cranialis posterior in the anterior part of the otic region and 

 bounded anteriorly by the crista sellaris. The antero-lateral 

 margins of the basal plate are extended ventro-laterally beyond 

 the connection with the otic capsule, and form the posterior end of 

 the crista pterygoidea. The lateral margin of the basal plate 

 extends laterally, beyond the anterior and middle thirds of the 

 capsule, as the crista substapedialis {est., fig. 4). Posterior to 

 the level of the fenestra vestibuli the lateral margin of the basal 

 plate passes into the lateral capsular wall ; in front of this fenestra, 

 however, the lateral extension of the basal plate becomes gradually 

 more pronounced. 



The basal 'plate and otic capsule are in connection with each 

 other for a considerable space, extending from the fenestra pro- 

 otica in front to the foramen jugulare behind and interrupted 

 only by the foramen facialis which is well in front of the cochlear 

 portion of the otic capsule and separated from the fenestra pro- 



