ENAMEL 65 



as projecting obliquely directed fibres, sometimes showing . 

 a zigzag splitting like an edge of fractured glass. These 

 processes are seen to pass all across the prism as well as 

 project from its edges, and Von Ebner has figured them in 

 human enamel as enveloping the concavo-convex prisms 

 like a sheath and projecting on either side. These wing 

 processes are visible not only in forming enamel but also in 

 the completed tissue, and can be seen in thin sections as 

 well as in teased preparations. In some ground preparations 

 made by the author to investigate these observations of 

 Smreker the wing processes of the prisms are distinctly 

 visible in some parts of the sections, and, as will be explained 

 farther on, they are still more conspicuous in the enamel 

 of the elephant. Here and there in teased preparations, 

 portions of membrane-like expansions are seen attached to 

 the prisms, but Von Ebner does not consider, for the reasons 

 given in his paper, that these are identical with the wing 

 processes (Plate III, fig. 12). 



The connecting processes between the prisms have been 

 described by Leon Williams, and are no doubt the processes 

 which form the intercolumnar bridges of Von Ebner. They 

 can be seen in thin sections of enamel, but are said by 

 Von Ebner not to be visible in transverse sections. A pre- 

 paration of the author's, however, shows them quite clearly 

 in transverse section, and they are still more evident in 

 Elephant enamel (Plate III, fig. 6, and fig. 29). 



In all teased preparations of human and other mammalian Needle- 

 enamels the broken prisms are seen to terminate in needle- splitting. 

 like oblique points at one end and sometimes at both ends of 

 the fractured prism (Plate III, fig. 9, &c.). This appearance 

 can be seen over the whole field of the microscope, and it is 

 seldom that a direct transverse fracture can be detected. 

 This needle-like splitting was considered by Von Ebner 

 to be due to the obliquely directed wing processes, but, as 

 it is seen in marsupial enamel where the wing processes are 

 very distinct and have a direction almost at right angles 

 to them, it is a little difficult to understand that this can 

 be the correct explanation of their origin. 



The direction of the splitting would appear to suggest 

 that it takes place along the lines of the Tomes' processes 



