698 B. W. KUNKEL 



the columella auris rests ventrallj-, and under which the ramus 

 communicans n. faciaUs cum glossopharyngeo lies. The antero- 

 lateral margin of the basal plate projects as a long ridge which 

 passes directly into the trabeeula cranii in front. This is the 

 crista basipterygoidea {pr.h., fig. 7) and represents the processus 

 basipterygoideus of Laeertk, as will be shown later. It is inclined 

 slightly ventrally so that a shallow groove is formed along the 

 margin of the ventral surface of the basal plate in which lie the 

 ramus palatinus n. faciaUs and arteria carotis interna (fig. 7). 

 Accordingly it corresponds to the sulcus cavernosus of the adult 

 pterygoideum {s.c, fig. 25). 



The dorsal surface of the basal plate exhibits a longitudinal 

 ridge in the middle line which becomes less conspicuous poste- 

 riorl}', disappearing completely in the condylar region. It is pro- 

 duced by the chorda dorsahs whose diameter is greater than the 

 vertical thickness of the basal plate along the middle hhe. The 

 thickness of the basal plate varies, decreasing markedly from the 

 posterior end. 



The fenestra basicraniahs posterior (f.b.p., fig. 25) is of a broad, 

 hexagonal form with anterior and posterior margins extending 

 transversely and with lateral angles. It lies in the anterior half 

 of the basal plate between the anterior portions of the two otic 

 capsules, with its anterior margin formed by the crista sellaris. 

 At the stage modelled it is closed by a membrane of dense con- 

 nective tissue beneath which the chorda dorsalis extends. 



The crista sellaris (c.s., fig. 25) forms a heavy transverse bar 

 between the fenestra basicraniahs posterior behind and the fen- 

 estra hj'pophyseos in front. In the mid-ventral line it exhibits 

 a pronounced longitudinal 'ridge, separating two longitudinal 

 grooves, while its lateral margin projects freely ventro-laterally 

 continuous with the crista basipterygoidea. Within the groove 

 thus formed, between the median crest of the crista sellaris and 

 the projecting lateral crests, lie ramus palatinus n. facialis and 

 arteria carotis interna. • 



Between the crista inferior and the pars lateralis of the occipital 

 region extends the sulcus supracristularis, a wide groove facing 

 laterally. In front it is hmited by the posterior wall of the otic 



