674 ANATOMY OF THE MUZZLE OP ORNlTHORHYyCHUS, 



the reflection of the Malpighian layer of the epidermis. It will 

 be observed, on reference to fig. 2, that the flattened epithelial 

 squames of which the upper part of the core of the cylinder 

 (probable hair shaft) is composed project vertically at the surface, 

 and, the constituent cells becoming more or less separated from 

 each other, form a brush-like arrangement which usually projects 

 slightly above the general surface of the epidermis. According to 

 our observations upon perfectly prepared material ^Flemming's 

 fluid, alcohol, and Miiller's fluid), this mass of cells never con- 

 stitutes a solid plug, as Poulton has figured it, but exhibits the 

 loose and brush-like arrangement represented in fig. 2, the duct 

 passing through it to reach the surface. 



Towards the base of the cylinder, where it enlarges to form a 

 bulb, the arrangement of cells does indeed, as Poulton points out, 

 very strikingly suggest the bulb of a hair. This resemblance is 

 perhaps best seen in transverse sections (fig. 6). In this situation 

 the squames and cuticular cells surrounding the duct, which in 

 the upper portion of the cylinder form its core, both become 

 continuous with a mass of polyhedral cells (figs. 2 and 5, p). 

 Amongst these polyhedral cells the duct of the gland passes in an 

 irregular manner (fig. 2, d). The cells lining the lumen are not 

 differentiated from the others, and their edges are ragged both 

 here and upwards throughout the course of the duct. 



Previous to entering the bulbous base of the cylinder the duct 

 is composed of two regular layers of cubical cells (fig. 2, d,). At 

 the point of entry the external layer becomes continuous with the 

 outermost layer of cells forming the follicle, and the internal 

 although differentiated from the polyhedral cells for a short 

 distance, by taking the stain a little more deeply, soon becomes 

 absolutely continuous with them. 



In describing this epithelial cylinder Mr. Poulton says:—" The 

 general epidermis is continued over it as a sheath, which strongly 

 suggests the outer root-sheath of a hair, and between it and the 

 cylinder itself a line of separation tends to appear." He also 

 figures such a separation of the core from its sheath in his fig. 8. 

 We have also noticed the same tendency of the core to shrink 



