616 JOHN D, KERNAN, JR. 



face of the dorsum sellae. The ventral surface of the otic portion 

 of the basal plate (fig. 3), craniad to the primitive break, becomes 

 convex from side to side and continues its horizontal direction. 

 This divergence of the surfaces causes a dorso-ventral thickening 

 of the cartilage which is much more marked further craniad in 

 the orbito-temporal region (fig. 2). The line of demarcation 

 between otic and orbito-temporal regions may be placed at the 

 beginning of the rise of the surface to the dorsum sellae. 



The otic capsules are firmly fused to each side of the otic 

 portion of the basal plate, which they deeply indent and so nar- 

 row. Of the character of the fusion, I have already spoken (fig. 

 5). The line of fusion is marked dorsally and ventrally by deep 

 grooves known as the basi-capsular grooves (DeBurlet). These 

 grooves together completely encircle the line of union and meet 

 cranially and caudally in notches, the spheno-capsular and occip- 

 ito-capsular respectively (figs. 1 and 3). The first is the primi- 

 tive carotid canal, the second is the ventral end of the jugular 

 foramen. 



The capsules have two other connections to surrounding parts. 

 The first is caudally through the occipito-capsular commissure 

 to the lamina alaris of the lateral occipital region; the second is 

 dorsally through the capsulo-parietal commissure to the parietal 

 plate (figs. 2 and 7). 



The otic capsule consists of two parts, (fig. 1) the cochlear, 

 which contains the vestibule and cochlea; and the canalicular, 

 which contains the semicircular canals. While the cartilage of 

 these regions is continuous and the capsule appears in a single 

 mass in reconstruction, on microscopic examination the cochlear 

 part is found to be much younger, an evidence of the retardation 

 of its chondrification, which is the usual condition in mammals. 

 The union between the two is marked cranially and caudally 

 by notches which correspond to the superior and inferior otic 

 notches of Macklin (figs. 1 and 3). Mesially, the surfaces of the 

 two parts pass smoothly into one another without demarcation. 

 The line of union seen from below (fig. 3), is a deep groove in 

 which the facial nerve passes forward to enter the skull by turn- 

 ing dorsad through the superior otic notch. The ventral sur- 



