File:Streeter1906 plate02.jpg

The colors, yellow and red, are used to indicate respectively the cochlear and vestibular divisions, and in general nerve flbers can be distinguished from ganglion cell masses by their lighter tone. The pictures represent a magniflcation of 25 diams.

The last step in its differentiation consists in the widening of the distal end into a flattened pouch or sac, in contrast to the remainder, which persists as a narrow duct connecting it with the vestibule, indicated in Figs. a, b, c, Plate II.

The thickness of the epithelium of the outer edge and presence of division figures indicate that the activity of growth still continues. Section D shows a canal in an embryo 30 mm. long, the same stage as that shown in Figs. a, b, c, Plate II.

The initial ingrowth of the membranous partition can be seen in Figs. 1 and m, where it can be distinguished as a horizontal cleft which forms in front between the utricular and saccular parts of the atrium. Strictly speaking we cannot speak of a saccule and utricle until the intervening partition is complete. It is practically complete in Figs. a, b, c, Plate II; here it reaches back to the entrance of the ductus endolymphaticus. It later divides the orifice of that structure, thus affording it separate openings into the utricle and saccule, the two openings constituting the so-called ductus utriculo-saccularis.

• absorpt. focus - area of wall where absorption is complete.
• amp. - ampulla membranacea.
• crus - crus commune.
• c.sc.lat. - ductus semicircularis lateralis.
• c. sc. post. - ductus semicircularis posterior.
• c. sc. sup. - ductus semicircularis superior.
• coch.orcochlea - ductus cochlearis.
• duct. endolymph. - ductus endolymphaticus.
• d. reuniens - ductus reuniens Henseni.
• endol. or endolymph. - appendix endolymphaticus.
• rec. utr. - recessus utriculi.
• sacc. - sacculus.
• sac. endol. - saccus endolymphaticus.
• sinus utr. lat. - sinus utriculi lateralis.
• utric. - utriculus.
• vestib.p. - vestibular pouch.