EAR 



467 



tube is the ductus cochlearis; its distal end is the cacum cupulare, and at its 

 proximal end is the cacum vestibulare (Fig. 472, D, c. .). A dilated sac 

 formed at its proximal or upper end, opposite the caecum vestibulare, is 

 known as the sacculus; in the adult the connection between the sacculus 

 and ductus cochleae is relatively narrow, and is called the ductus reuniens 

 (Fig. 481). The portion of the original vesicle between the sacculus and 

 utriculus, from which the endolymphatic duct arises, becomes a compara- 

 tively slender tube, the ductus utriculo-saccularis (Fig. 481). 



The ectodermal vesicle thus produces a complex system of connected 

 epithelial ducts, namely the superior, posterior, and lateral semicircular 



Semicircular duct. 



Blood vessel. *~ 



Wall of the semi- 

 circular duct. 



-- Epithelium of the duct. 



Ligament of the duct. 



Bone?of the semicircu- 

 lai*canal. 



Ligament. 



Perilymph spaces 



Blood vessel. 



FIG. 473- CROSS SECTION OF A SEMICIRCULAR DUCT AND THE ADJACENT PERILYMPH SPACES TOGETHER 

 WITH THE SEMICIRCULAR CANAL OF BONE IN WHICH THEY ARE LODGED. From a human adult. X so. 



(B6hm and von Davidoff.) 



ducts; the utriculus, and utriculo-saccular duct with the endolymphatic 

 duct connected with it; the sacculus, ductus reuniens and ductus cochleae. 

 They all contain a fluid called endolymph. The acoustic nerve sends 

 branches between the epithelial cells in certain parts of the ducts. Round 

 areas of neuro-epithelium, in which the nerves terminate, are called 

 macula acustica; there is one in the sacculus and another in the utriculus. 

 Elongated areas are crista, and there is one in each of the three ampullae. 

 The axis, or modiolus, about which the cochlear duct is wound, contains 

 the nerves which send terminal fibers to the spiral organ of the adjoining 

 epithelium. In this they form a line of terminations along the medial 

 wall of the cochlear duct, following its windings from base to cupola. 



