362 CHARLES CLIFFORD MACKLIN 



though it falls a Uttle short of reaching either of these extremities 

 (fig. 6). It is known as the sulcus caroticus (Voit) and contains 

 a portion of the internal carotid artery (fig. 13). The sulcus 

 caroticus does not correspond to the line of attachment of the 

 lamina spiralis within, but crosses its cranio-ventral convex 

 portion. Its lower part forms a low rounded projection into the 

 lumen of the uncoiled portion of the cochlear duct, which appears 

 in the figure of the cast of the cavity (fig. 8) as a shallow fossa. 



The dorsal part of the lateral surface is made up principally 

 by the outer wall of the vestibular portion, and forms the medial 

 wall of the ventro-lateral otic recess. Above, the outlet of the 

 facial foramen is to be seen, bridged by the suprafacial commis- 

 sure. Below this opening is a small groove, the sulcus facialis 

 (Voit), for the facial nerve, and below this, again, appears the 

 elongated, crescentic, fenestra vestibuli, lying in a general direc- 

 tion from above downward and backward, and presenting a 

 concavity downward and forward. It contains the anlage of 

 the footplate of the stapes, which, however, fills only a small 

 portion of the space of the fenestra, the remainder being occupied 

 by the connective tissue representative of the annular ligament 

 of the base of the stapes. Below the fenestra vestibuli is the 

 cartilaginous septum which separates it from the fenestra perilym- 

 phatica below. This septum, which acts as a commissure to 

 join the promontory of the pars cochlearis with the ventral 

 surface of the pars canalicularis, has been referred to by Voit 

 as the promontorium (fig. 6). 



Passing below the lower, downwardly concave, border of 

 the promontorium we come upon the small caudal surface of 

 the vestibular portion (fig. 2), marked centrally by the large 

 fenestra perilymphatica, which will later be separated by the 

 processus interperilymphaticus into the larger lateral fenestra 

 cochlearis or rotunda (over which is stretched the membranous 

 anlage of the membrana tympani secondaria), and the smaller, 

 medial foramen for the aquaeductus cochleae, within which may 

 by seen the saccus perilymphaticus (Voit). The interperilym- 

 phatic process, more prominent on the left side than on the 

 right, has been referred to, and appears as a short, conical 



