Volumetric and dimensional measurements of vestibular structures in the squirrel monkey.

Temporal bones of squirrel monkeys which were sectioned either in the routine horizontal plane or in the exact plane of lateral semicircular canal, were used for the volumetric and dimensional measurements. Endolymphatic volumes of utriculus, sacculus, lateral ampulla, lateral semicircular duct, and some related perilymphatic volumes were measured with the aid of a computer. The sizes of the duct-ampulla junction, ampulla-utriculus junction, duct-utriculus junction, etc. were also measured. The endolymphatic volume in the lateral ampulla was about 50% greater than that in the lateral semicircular duct. The endolymphatic volume involved in the rotation in the lateral canal plane was 2.188 mm3. Among those the utriculus was about half and the other half was the ampulla plus the duct. Furthermore, we measured the circumferences of the membranous semicircular ducts both in freshly dissected materials and in processed temporal bones. A statistically significant difference (p less than 0.01) was found between them. The actual tissue shrinkage factor was 9.2-9.3%.