GENERAL OBSERVATIONS 49 
Tae Suporirerous orn Swear Guanps are composed of 
coiled tubes which lie in the deeper portion of the skin, 
and send up a corkscrew-like duct to open on the surface 
of the epidermis. They are numerous over the whole of 
the body. 
Tue Human Natts are thickenings of the lowermost layer 
of the horny portion of the epidermis, the stratum lucidum. 
They are developed over a modified portion of the corium 
known as the nail-bed. The horny substance of the nail 
is composed of clear horny cells, and rests immediately 
Fie. 25.—LoncITUDINAL SECTION THROUGH NaIL AND NAIL-BED 
oF A Human Foran Fincer.* 
a, The nail; b, the rete mucosum ; ¢, the longitudinal ridges of the corium. 
upon a Malpighian layer similar to that found in the 
epidermis generally. Instead of the papille present else- 
where in the skin, the corium of the nail-bed is marked 
by longitudinal ridges, a similar, though less distinct, 
arrangement to that found in the lamine of the horse’s 
foot. 
* Seeing that the section is a longitudinal one, it would appear from 
the way the ridges cut that they are running transversely beneath 
the nail. Their extreme delicacy, however, prevents a single one 
showing itself along the length of the section, and their constant 
accidental cutting makes them appear to run transversely (H. C. R.). 
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