252 HENRY C. TRACY 



Fig. 11 Drawing to show the membranous labyrinth and the subcerebral 

 perilabyrinthine plate and canals in relation to the floor and side of the skull. 

 Drawing somewhat diagrammatic, based on dissections and a model. The 

 upper half of the cranial wall and of the semicircular canals have been dissected 

 away. The specimen is cut in the median sagittal plane which shows at the right 

 side of the figure; a second cut parallel to this and about half-way to the outside 

 separates the specimen into two parts which are represented as being slightly 

 separated. In the median plane are shown the utricular and saccular sub- 

 cerebral canals; in the second plane are shown the relations of the utricular 

 subcerebral canal where it is divided into two parts by the lips of the fenestra 

 of the anterior osseous capsule; the two parts of the canal connect laterally 

 under the utriculus with the lateral recess of the skull (fig. 12). The relation 

 of the recessus utriculi to the fenestral lips and to the two chambers of the 

 anterior osseous capsule are also shown. The canal for the precoelomic diverti- 

 culum is cut obliquely just before its entrance to the capsule. The cavity of 

 the posterior osseous capsule is cut into slightly on its median side. Pomolobus 

 pseudoharengus. 



Fig. 12 Lateral dissection of the labyrinth and perilabyrinthine structures. 

 The utriculus rests on the lips of the fenestra with a division of the utricular 

 subcerebral canal (USCP, USCA) on either side. These relations are those seen 

 on looking medially toward the utriculus when the lateral recess of the skull is 

 opened up from the outside. Posteriorly in the drawing, the supracerebral 

 perilabyrinthine band springs from the base of the superior sinus. Accessory 

 plates of perilabyrinthine tissue can be seen applied to the outside of the utricu- 

 lus, the ampullae, the superior sinus, and the upper end of the anterior semi- 

 circular canal. The triangular projection of perilabyrinthine tissue (TPP) is 

 probably the 'bulbe accessoire' of Breschet. An opening through this (not 

 shown in the figure) puts the lateral recess in communication with tissue spaces 

 lateral to the superior sinus and hence with the supracerebral canal (PSC) 

 through its irregular opening. 



Fig. 13 Diagram of a sagittal section of the anterior osseous capsule and 

 septum: orientation figure for figure 14. Pomolobus pseudoharengus. 



Fig. 14 Drawing to show the histological detail of the septum and its attach- 

 ment to the wall of the anterior osseous capsule. The elastic plates of which the 

 septum is made up anastomose freely as they approach the bone and arc attached 

 by white connective-tissue fibers which pass into irregular radial canals in (he 

 bone. The periosteum of the two chambers is reflected onto the surfaces of the 

 septum. 



