406 W. G. RIDEWOOD. 



trace of medulla. The width is very uniform, and measures 

 170 n througliout tlie middle six eighths of the hair. The 

 basal eighth is slightly narrower, and the free end tapers 

 gradually to a blunt point, which is missing from most of the 

 hairs. A perfect hair measures about 6 cm. in length.^ The 

 cortex would be quite clear and homogeneous but for the few 

 short, fusiform air spaces, which are visible both from the 

 side and in transverse sections. The vacuoles are uniformly 

 distributed in all my preparations, and I have been unable to 

 discover the peripheral clear zone of the cortex mentioned and 

 figured by Jacob (4, p. 62 and fig. 2). Transverse sections 

 from different parts of the hair are all similar in character 

 (fig. 24). 



The cuticle is moderately thick, and stains deeply. When 

 the hair is examined from the side the cuticular scaling is 

 very clearly observable on the basal third (fig. 25), but 

 cannot be seen over the rest of the hair. This fact, together 

 with a certain anxiety to make this ground sloth conform in 

 its hair structure with the tree sloths, has led Ltinnberg (7) 

 to conclude that the hairs of My lo don List ai, as we know 

 them, are but the central cores of hairs which were provided, 

 like those of Brady pus, with a more perishable extra- 

 cortical layer. The fragments of adhering material, however, 

 which he alludes to as the remains of the extra-cortex, are, 

 judging by my own preparations, nothing but foreign matter 

 such as di-ied mud or portions of the shrivelled root-sheath. 

 On the basal part of the hair of the human head organic 

 cellular substance, probably derived from the inner root- 

 sheath, is commonly found attached to the cuticle long after 

 that part of the hair on which it is found has emerged from 

 the follicle. The fact of the cuticular scaling showing 

 only on the basal part of the hair appears at first sight to 

 support Lonnberg's view, for in Brady pus the extra-cortex 



1 The observations were made upon the specimen describetl by Smilli 

 AVoodward and Moreno in 1899 (18). In a more recently discovered speci- 

 men, less well preserved, the hairs are much longer. See Smith Woodward 



(19). 



