98 FRANKLIN PEARCE REAGAN 



having as a base the lateral extent of the parachordal. This 

 cartilage seems to be comparable to that which is found mesial 

 to the auditory epithelium on the normal side. Dorsal to the 

 facial nerve will be noticed a section of the cartilage which forms 

 the roof of the capsule which surrounds that nerve. It is evi- 

 dent that the cartilages surrounding the facial nerves on the two 

 sides are in every way comparable. There is reason to believe 

 that these two cartilages, portions of the otic capsule, perhaps, 

 have arisen in response to the presence of the facial nerve, 

 acoustico-facialis ganglion, and the portion of the otocyst which 

 was moved into the potential region of the foramen for the facial 

 nerve. In some cases it was observed that the acoustico-facialis 

 ganglion, by reason of its intimate connection with the otocyst, 

 was removed with the latter, a cartilaginous covering for the 

 nerve failed to develop. Examination of figure 3 might seem at 

 first to afford evidence against this view, for we have 

 here a facial nerve which is not surrounded by a cartilage. In 

 figure 3, mesial and internal to the distal extent of the para- 

 chordal cartilage will be noticed an L-shaped cartilage which 

 might conceivably represent the cartilage described as the cap- 

 sule of the facial nerve in figure 5, having become displaced 

 through pressure. The conditions might easily be correlated 

 with the displacement of the trigeminal ganglion. There is 

 perhaps another alternative. It might be assumed that the 

 L-shaped cartilage or its normal homologue represents a portion 

 of the parachordal complex which arises independently of the 

 sensory epithelial tissue. In other words it might be assumed 

 that not all of the otic capsule arises in response to the sen- 

 sory epithelium, but perhaps in part to a stimulus from other 

 nervous tissue. In figures 5, 6, and 10, it will be seen that a 

 portion of the capsule surrounding the lagena on the uninjured 



Figs. 6 and 7 Photographs from a section which passed through the greatest 

 extent of the columellae of the same nine-day embryo from which figures 4 and 

 5 are taken. Figure 6 is from the normal side. Figure 7 is from the operated 

 side. Note that the columellae are about equal in length and that there is no 

 stapedial plate in figure 7. P. E. C. No. 1118. Qudr. at., otic process of the quad- 

 rate; T.p., tympanic pouch. (Other abbreviations as in figures 1 to 5). The 

 upper portion of the tympanic pouch in figure 6 was unfortunately labeled 

 'Qudr. ot.'i 



