32 IRVING HARDESTY 



ridge, and apexward from the cells producing them. The fibrils 

 of the outer side of the membrane are longer and curve out- 

 ward, apexward and axisward from the basal side, claimed as 

 due to first the great increase in width and then the decrease in 

 width of the greater epithelial ridge, both of which changes in 

 width occur after the beginning of the membrane. 



From the study of the adult, I see no reason for describing 

 the tectorial membrane in more than two zones, the attached 

 axial zone and the outspanning zone. To let Hensen's stripe 

 mark the boundary of a third zone is, I think, unnecessary other 

 than that the stripe forms the axial boundary of that width of 

 the membrane which projects beyond the interlocked phalanges 

 of the pillars of the spiral organ. A 'border plexus' or a thin 

 outermost zone does not exist in the adult nor in the older fetuses. 

 The outer edge of the membrane is bluntly rounded and, in con- 

 tour, slightly scalloped. The fibrils forming the edge curve 

 from the basal surface outward, around the edge and then apex- 

 ward and axisward. The appearance described by me as an 

 "accessory tectorial membrane" in the fetus is present on the 

 membranes of the adult hog. In one specimen of the teased out 

 membrane it appeared partly lifted away from the basal sur- 

 face in places but in none of the mounts from the adult was it 

 so completely lifted away from the main body of the tectorial 

 membrane and so separately visible as in the specimen from 

 the fetus described and illustrated in the previous paper. 



Held ('09) described the thickness of the tectorial membranes 

 of the rabbit as composed of three layers: A 'Decknetz' on the 

 apical surface; a middle fibrillar layer on the main body of the 

 membrane composed of fibrils embedded in a matrix (Zwis- 

 chensubstanz), and a thin homogeneous layer bounding the 

 basal surface. All three layers come together in the outer edge 

 of the membrane which he calls 'the selvage' and which he 

 describes as blunt and irregularly fibrous. By irregularly fi.brous 

 is meant that bundles of fibrils curve around the selvage giving 

 it the lobed or scalloped appearance in contour mentioned above. 

 His descriptions of the course of the fibrils and their abundance 

 conforms in the main with mine. 



