228 HENRY C. TRACY 



the skull between the two lateral recesses. It begins on each 

 side under the utriculus where it occupies the whole space 

 between the floor of that structure above and the surface of the 

 anterior osseous capsule below (fig. 12). It is partially sub- 

 divided into an anterior and posterior part by the projecting 

 lips of the fenestra on which the utriculus rests (figs. 5, 9, 12, 

 and 17; USCA, USCP). In the utricular region the roof of the 

 canal is formed by the floor of the recessus utriculi in which 

 are located the divisions of the macula acustica utriculi. The 

 floor of the utriculus is very thin except under the divisions of 

 the macula. 



Laterally the canal connects freely with the tissue spaces 

 in the lateral recess under the arch made by the apposition of 

 the falciform process of the prootic bone with the projecting 

 anterior part of the pterotic bone. Thus, the lateral spaces 

 of each side communicate freely with each other through the 

 canal. There appears to be no obstacle to the free transmis- 

 sion of pressure changes from the outside through the lateral- 

 line canal and the lateral spaces to the two parts of the utricular 

 subcerebral canal and thence to the floor of the utriculus on 

 each side of the lips of the fenestra. 



A small blind extension of this canal passes up over the 

 mesial narrow side of the recessus utriculi in close relation to the 

 epithelium. From the space between the utriculus and the 

 anterior osseous capsule, the canal passes medially straight 

 across the floor of the skull under the brain to become con- 

 tinuous with the corresponding structure of the other side 

 (% 11). 



The utricular subcerebral canal is the best-defined of all the 

 perimeningeal spaces. It is easily visible to the naked eye and 

 has been observed by all investigators from Weber on. Weber 

 and Ridewood considered it an endolymphatic canal. I have 

 studied many series of sections of young and adult Clupeoids, 

 and there can be no doubt whatever that it is a tissue space, 

 differentiated from the perimeningeal tissue under the mem- 

 branous labyrinth and brain. Tysowski and de Beaufort, the 

 only investigators to study the canal with modern technic, 

 emphatically testify to the same conviction. 



