1048 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 



the anterior end of which is named the pyramid of the vestibule. This ridge bifur- 

 cates below to enclose a small depression, the fossa cochlearis, which is perforated 

 by a number of holes for the passage of filaments of the acoustic nerve which supply 

 the vestibular end of the ductus cochlearis. As the hinder part of the medial wall 

 is the orifice of the aquaeductus vestibuli, which extends to the posterior surface of 





FIG. 920. Right osseous labyrinth. Lateral view. 



the petrous portion of the temporal bone. It transmits a small vein, and contains 

 a tubular prolongation of the membranous labyrinth, the ductus endolymphaticus, 

 which ends in a cul-de-sac between the layers of the dura mater within the cranial 

 cavity. On the upper wall or roof is a transversely oval depression, the recessus 

 ellipticus, separated from the recessus sphsericus by the crista vestibuli already 

 mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated 



Recessus ellipticus 

 Recessus sphcericus 



Orifice of aquceductus vestibuli 



Fossa cochlearis 

 Cochlear fenestra 



Orifice of aquceductus cochleae 



FIG. 921. Interior of right osseous labyrinth. 



by a number of holes (macula cribrosa superior). The apertures in the pyramid 

 transmit the nerves to the utricle; those in the recessus ellipticus the nerves to the 

 ampullae of the superior and lateral semicircular ducts. Behind are the five orifices 

 of the semicircular canals. In front is an elliptical opening, which communicates 

 with the scala vestibuli of the cochlea. 



