230 HENRY C. TRACY 



The labyrinth lies in the auditory recess suspended there by 

 the thickenings and processes of the compact perilabyrinthine 

 tissue. The utriculus occupies the lateral and anterior part of 

 the recess. The recessus utriculi is enlarged transversely into 

 a flattened somewhat wedge-shaped chamber. The narrow 

 part of the chamber extends a little under the brain mesially 

 while the broader part fits up under the arch made by the falci- 

 form process and the projecting part of the pterotic bone, and 

 is thus in relation by its lateral surface to the lateral recess of 

 the skull; ventrally, the surface of the recessus utriculi rests 

 directly on the lips of the slit-like fenestra of the anterior bony 

 capsule (fig. 12). Sections show conclusively that no part of the 

 labyrinth enters the fenestra. What Weber and Ridewood mis- 

 took for a utricular diverticulum is merely the tissue space in 

 the upper chamber of the osseous capsule above the septum. 

 Under the recessus utriculi is the subcerebral perilabyrinthine 

 canal, which, as described above, is here subdivided into an 

 anterior and posterior canal (USCA, USCP) by the projecting 

 lips of the fenestra as a result of their attachment to the floor 

 of the utriculus. 



The macula acustica utriculi is differentiated into three parts 

 which run transversely across the floor of the broad wedge- 

 shaped recessus utriculi; the anterior division (fig. 17, MA A) 

 lies along the line of attachment of the floor of the recessus 

 utriculi to the anterior lip of the slit-like fenestra of the anterior 

 osseous capsule; the middle division (MAM) runs along the line 

 of attachment to the posterior fenestral lip; the posterior divi- 

 sion (MAP) lies a little farther back, and in no particular rela- 

 tion to structures outside the utriculus. These three divisions 

 slightly diverge laterally; mesially they unite in a common area 

 which lies in the narrow part of the wedge-shaped recessus 

 utriculi nearly over the mesial end of the fenestra. Under each 

 division of the macula, the tunica propria is rather thick and 

 contains the branches of the eighth nerve which supply the 

 macular cells. The middle band of the thickened tunica pro- 

 pria under the middle division of the macula is shaped like a 

 three-sided prism which is attached by its edge to the posterior 



