326 



GEOEGINA SWEET. 



Part IV.- — The Skin, Hairs, and Certain Associated Structures. 



The skin forming- the surface of the body generally, con- 

 sists of two or three layers of cells, covered by a thin corneous 

 layer (PL 19, figs. 3, 4, 12, e.). Over the snout and tail 

 the epidermis becomes most highly developed forming the 

 strong horny coverings to those parts. The skin undergoes 

 modification, also in the region of the special " ischiotergal 

 patch, '^ on the hinder part of the back, overlying the ischio- 

 tergal slip of muscle previously referred to by Dr. Stirling 

 [10, p. 159], Professor Baldwin Spencer [8, p. 4G], and Pro- 

 fessor Wilson [13, p. 6]. The diameter of this patch varies 

 as measured in sections, from 9 mm. to 10 mm., 9 6 mm. 

 being an average width. It can always be seen from the 

 exterior by its darker golden-brown colour. 



The varying thickness of the skin in different parts is seen 

 in the following table : 



Thickness of 



Snout 



Chin and Side of 

 Head. 



Stratum Corneum "IS mm. 

 „ lucidum rO^ mm, 

 „ Malpiglii''071 mm, 



:} 



•009 to -014 mm. 

 •01 to -021 mm. i 



Total thickness of 



Epidermis . -244 mm.' "019 to 'OSS mm. 



Total thickness of 



Dermis . . "3 mm.' "85 mm. 



General 

 Surface. 



•040 mm. 

 014 mm. 

 034 mm. 



0S8 mm. 



Centre of Ischi- 

 otergal Patch. 



•018 to •021mm. 

 •007 to^012 mm. 

 •050 to •063 mm. 



•075 to •Ogo mm. 



■52 mm. 



1-54 to 2*45 mm. 



The thinness of the dermis in the snout is due to the 

 absence of hairs in that part, while in the chin and general 

 surface of the body, and especially in the ischiotergal patch, 

 these structures are highly developed. Immediately below 



