3 8o 



HISTOLOGY. 



While the formation of the semicircular ducts is occurring in the upper 

 part of the vesicle, the lower portion elongates and its end becomes coiled, 

 eventually making two and a half revolutions. The coiled tube is the 

 ductus cochleae; its distal end is the caecum cupulare and at its 

 proximal end is the caecum vestibulare (Fig. 430 D, c. v.}. A dilated sac 

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

 sacculus; in the adult the connection between the sacculus and ductus 

 cochleae is relatively narrow and is called the ductus reuniens (Fig. 439). 

 The portion of the original vesicle between the sacculus and utriculus, 

 from which the endolymphatic duct arises, becomes a comparatively 

 slender tube, the ductus utriculo-saccularis (Fig. 439). 



ds.p. 



FIG. 430. LATERAL OR EXTERNAL SURFACES OF MODELS OF THE MEMBRANOUS PORTION OF THE 

 LEFT INTERNAL EAR FROM HUMAN EMBRYOS. Different enlargements. (After His, Jr.) 



A, from an embryo of 6.9 mm.; B, 10.2 mm.; C, 13.5 mm.; and D, 22 mm. am., ampulla; c. v., caecum 

 vestibulare of d. c., cochlear duct; d. e., endolymphatic duct; d. s. 1., d. s. p., and d. s. s., lateral, 

 posterior, and superior semicircular ducts; sac., sacculus; ut., utriculus. 



The ectodermal vesicle thus produces a complex system of connected 

 epithelial ducts, which are the superior, posterior, and lateral semicircular 

 ducts, the utriculus the 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 terminates 

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

 Round areas of neuro-epithelium are called maculae acusticae; there is one 

 in the sacculus and another in the utriculus. Elongated areas are cristae 

 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 cupula. 



The mesenchyma immediately surrounding the system of ducts 



