EAR-SWIMBLADDER RELATION IN CLUPEOIDS 225 



mals. This differentiated tissue is compact, elastic, tough, and 

 translucent, and is apparently composed of flattened bands, or 

 sometimes of irregular plates of fibro-elastic tissue so closely 

 held together by a cement substance that in sections it appears 

 in most places almost as homogeneous as the matrix of cartilage. 

 Flattened, stellate cells occupy irregular spaces between the 

 fibrous elements. 



In the Clupeoids, this differentiated tissue is not confined to 

 the cells and fibers immediately adjoining the epithelium of the 

 labyrinth, but forms definite processes and extensions which 

 reach into remote parts of the perimeningeal tissue. These are 

 the structures referred to as perilabyrinthine plates or processes 

 to distinguish them from the undifferentiated portions of the 

 perimeningeal tissue. 



The most extensive of these perilabyrinthine structures in- 

 volves the greater part of the perimeningeal layer under the 

 brain. It takes the form of a horizontal plate (subcerebral 

 perilabyrinthine plate) which connects the thickened walls of 

 the utriculi of the two sides under the brain (figs. 8 and 11, SPP). 

 Anteriorly it extends a short distance in front of the utriculus 

 and its edge curves downward to become attached to the peri- 

 osteum on the surface of the anterior bony capsules of the two 

 sides and the ridge of bone connecting them (fig. 12, SPP). 

 The lateral edge of this forward extension of the plate in front 

 of the utriculus is attached to the arch leading to the lateral 

 recess of the skull (i.e., to the falciform process of the prootic 

 bone); over the utriculus, the lateral part of the plate is con- 

 tinuous with a sharp ridge-like thickening of the differentiated 

 perilabyrinthine tissue of the utricular roof which is continuous 

 with the thin perimeningeal tissue which lines the cartilage in 

 the lateral wall of cranium (fig. 11,*). Posteriorly the plate is 

 attached to the free anterior edges of the triangular plates of the 

 two exoccipital bones, so as to roof in the saccular recess on 

 each side. Thus the plate, with the connected thickening of the 

 utricular roof, forms a 'false bottom,' so to speak, of the cerebral 

 cavity, and by its continuous attachment with the margins of 

 the auditory recess completely excludes the latter from direct 



