36 



NORTH AMERICAN FAUNA 68 



Figure 18. — Cross section of pelage (by Hardy device) about 10 mm. from 

 surface of skin, near midback, adult male sea otter D22-57. The large 

 guard hairs are oval in cross section at this level, and their surface is 

 crenulated. The much smaller and numerous fur hairs tend to be 3 or 4 

 sided. Magnification X 430. (VBS 5712 and 5713) 



also 50 microns, and the reticular layer makes up the remainder. The longest 

 underfur hairs measure up to 22 mm in length, of which 19 mm may protrude 

 beyond the surface pore of the hair canals. 



Five layers, stratum corneum, stratum granulosum, stratum lucidum, 

 stratum spinosum and stratum germinativum, are recognizable in the epider- 

 mis. The granular layer is not uniformly dense throughout and pigment is 

 absent. . . . The epidermis is thrown into a series of folds which are re- 

 flected by similar folding of the papillary zone of the dermis. Collagen fibres 

 in the deeper dermis are oriented both randomly and parallel to the skin 

 surface. Arrector pili muscles are absent. 



Hair follicles are arranged in bundles and are aligned at an angle of about 

 70° to the skin surface. Each bundle comprises a guard hair follicle and 

 underfur follicles, which are separated from each other near their base but 

 are held together closely at higher levels. In cross section there is some 

 suggestions of trio grouping with a central guard hair follicle between two 

 other guard hair follicles. The underfur follicles open into the guard hair 

 canal and all hairs emerge at the skin surface through a common pore 

 [fig. 17]. 



Cutaneous glands associated with each guard hair follicle and opening into 

 the bottom of the guard hair canal comprise a bilobed sebaceous gland and a 

 greatly coiled apocrine sweat gland. The sweat duct opens posterior to, and 

 slightly higher than the common sebaceous duct formed by the union lower 

 down of separate ducts from each gland. Keratohyalin granules abound near 



