314 KOBERT J. TERRY 



Figure 6 made from a van Wijhe preparation of 12 mm. shows 

 the otic capsule from its medial side. Only those parts appear 

 which are chondrified. The three semicircular ducts are in large 

 part walled by cartilage. The blue stain is most intense upon the 

 lateral aspect, faint on the medial side of the ducts. The parietal 

 plate is a small triangular cartilage, lying dorsad of the interval 

 between the posterior semicircular canal and the lateral occipi- 

 tal arch. It is entirely independent of other cartilages of the 

 cranium. 



The first trace of chondrification of the otic capsule was found 

 in embryos of about 10 mm. (fig. 5). In van Wijhe specimens of 

 this stage a narrow streak of blue follows the dorsal and lateral 

 circmnferences of the anterior and posterior semicircular canals. 



Nerves in the otic region 



A brief description of the nerves and blood vessels which have 

 been referred to in the description of the otic region will serve to 

 correlate the many structures which have just been described. 

 The roots of the trigeminal nerve pass forward over the supra- 

 facial commissure and through the septum transversum (vide 

 infra), to the semilunar ganglion, the caudal half of which rests 

 upon the planum supracochleare. The abducent nerve runs 

 along the medial side of the cochlear capsule, leaving the otic 

 region by passing forward between this structure and the dor- 

 sum sellae. The seventh nerve, together with the vestibular 

 and cochlear divisions of the acustic, enter the internal acustic 

 meatus from before backward in the order named. The glosso- 

 pharyngeal, vagus and accessory traverse the jugular foram_en, 

 behind the otic capsule. 



The facial nerve, including the pars intermedia (figs. 2, 4, 20, 

 21), is close to the ganglion of the vestibular nerve as it lies in 

 the internal acustic meatus. It passes through the primary 

 facial canal and the facial foramen to enter the cavum supra- 

 cochleare and there, outside of the cavity of the chondrocra- 

 nimn, presents upon its dorsal side the geniculate ganglion (fig. 

 20). Connected with the ventral surface of the latter is the great 

 superficial petrosal nerve. Its position is entirely extracranial. 



