1094 



SPECIAL SENSE ORGANS 



vestibular nerve, filaments of which extend from the middle macula cribrosa to 

 the anterior and medial wall of the saccule, to be distributed over a thickened 

 area, macula acustica sacculi. Anteriorly and inferiorly the saccule gradually 

 passes into a short canal, the ductus reuniens, which connects it with the cochlear 

 duct, and posteriorh* the very small endolymphatic duct is attached (fig. 839). 



Fig. 839. — Diagram of the Left Membranous Labyrinth. (Deaver.) 



Superior and lateral membranous ampuUee 



Superior semicircular 

 duct 



Cupular caecum 



Cochlear duct 



Posterior semicircular 



duct 



Ductus reuniens 

 Vestibular caecum 



Utricle 



Lateral semicircular duct 

 Posterior membranous ampulla 

 Ductus endolymphaticus 



This extends through the aquseductus vestibuli to the posterior surface of the 

 petrous portion of the temporal bone, where it ends in a dilated blind pouch, 

 the endolymphatic sac, situated just beneath the dura. Just beyond the saccule, 

 the endolymphatic duct is joined at an acute angle by a short canal of minute 

 calibre, the utriculo -saccular duct, which opens into the utricle through its anterior 

 medial wall and, with the endolymphatic duct, connects it with the saccule. 



Fig. 840. — Right Membranous Labyrinth of a Newborn Child. Exposed by Partial 

 Removal of the Bony Labyrinth. Dorsal view. (Toldt, "Atlas of Human Anatomy," 

 Rebman, London and New York.) 



Utriculo-ampuUary branch of the vestibular nerve 

 Utricle 



Facial nerve 

 Cochlear nerve i 



Plexus-like relation of fibre- 

 bundles of cochlear nerve 



Modiolus -- 



Osseous lamina- 

 spiralis 



Lamina basilaris 

 ^membranous ' 

 lamina spiralis) 



Scala tympani 



Superior semicircular duct 



Superior membranous 

 ampulla 



Common crus 



Posterior semicir- 

 cular duct 



Osseous semicir- 

 cular canal 



Saccule l Posterior membranous ampulla 

 Posterior ampullary nerve 



The semicircular ducts (membranous semicircular canals) are .situated within 

 the osseous semicircular itanals and are, therefore, known as the lateral, superior, 

 and posterior semicircular ducts. They connect with the utricle by five openings, 

 the posterior and superior ducts uniting to form a common crus before their 



