LABYRINTH 531 



and posterior to the saccule. Into it open the membranous semicircular 

 ducts which lie in the bony semicircular canals. 



Each semicircular duct corresponds in general form with the semi- 

 circular canal *In which it lies, but it is of smaller diameter. Its convex 

 margin is attached to the adjacent part of the wall of the bony canal. 



The saccule is smaller, and occupies the recessus sphaericus on the anterior 

 part of the medial wall of the vestibule. It communicates by means of a 

 short narrow tube, termed the canalis reuniens, with the ductus cochlearis 

 or membranous cochlear tube. 



The saccule and the utricle are only indirectly brought into communica- 

 tion with one another ; a slender tube termed the ductus endolymphaticus 



Ductus endolymphaticus 



Dura mate 

 Vestibule 



Osseous 

 cochlea 



Stapes 



Fenestra cochleae 



Aquaeductus cochlea 



FIG. 225. Diagram of the Osseous and Membranous Labyrinth. 

 (Modified from Testut.) 



U. Utricle. .S". Saccule. D.C. Ductus cochlearis. 



occupies the aquseductus vestibuli, and divides into two branches which 

 pass respectively into the saccule and the utricle (Fig. 225). 



The ductus cochlearis, or scala media, lies between the two scake of the 

 bony cochlear tube. It ends blindly at each extremity, but close to its 

 basal end it is brought into communication with the saccule by the canalis 

 reuniens. 



BULBUS OCULI. 



THE bulbus oculi or eyeball is not perfectly spherical. In- 

 deed, it may be said to be composed of the segments of two 

 spheres. The anterior or corneal segment, which forms 

 only about one-sixth of the entire eyeball, possesses a 

 shorter radius than the posterior or scleral segment. The 



