618 JOHN D. KERNAN, JR. 



foramen gaps widely ventrally, mesially and cranially. Evident- 

 I3', as comparison with my model shows, enclosure of this foramen 

 by cartilage begins caudally and laterally and proceeds craniad 

 and mesiad. This holds true for the whole cochlear portion, as 

 in Levi's 14 mm. model there is no cartilage about the cochlea 

 except caudally and laterally. 



The facial nerve (figs. 1 and 2) is directed laterad and craniad 

 from the internal acustic foramen to the cavum supracochleare 

 (Voit), passing between the pars cochlearis and pars canali- 

 cularis. It then turns sharply caudad, ventral to the bar of 

 cartilage which unites the pars cochlearis with the pars canali- 

 cularis. At this angle where its direction changes, it presents the 

 enlargement of the geniculate ganglion and gives off the great 

 superficial petrosal nerve. The portion of the nerve proximal 

 to the ganglion trans verses the primitive facial canal, which has 

 as yet no cartilaginous roof. Conditions here, in view of the 

 theoretical importance of the region, must be discussed in some 

 detail. At the site of the future mesial commissura supra- 

 facialis — this Voit holds to be equivalent to the commissura 

 praefacialis of reptiles — the pars canalicularis sends a small pro- 

 jection mesiad on the dorsal aspect of the nerve (fig. 1, SI). 

 This is directed towards the pars cochlearis, but is far from form- 

 ing a complete bridge. The commissura is well developed at 40 

 mm. (Macklin, fig. 6), and at 80 mm. it forms a broad unper- 

 forated roof to the facial canal (Hertwig, fig. 658). Fischer, 

 however, states that in a special model by Hertwig of the otic 

 region of this same human embryo, the roof of the facial canal is 

 perforated. In this he finds evidence of the existence' of two 

 suprafacial commissures in man, which he previously had ascer- 

 tained to be the case in Talpa, a medial and a lateral, one cross- 

 ing the facial nerve proximal, the other distal to the geniculate 

 ganglion. Of this second commissure there is no trace in this 

 embryo, nor does Macklin record its presence at 40 mm. Its 

 very late appearance in man would suggest the possibility of its 

 being of secondary nature, and in so far supports Voit's inter- 

 pretation of the mesial commissure as the fundamentally im- 

 portant one and equivalent to the commissura praefacialis of rep- 



