424 



INNERVATION. 



[CHAP. xiv. 



epidermic particles having a different arrangement from those of the 

 cuticle itself ; being flattened in the vertical instead of the horizon- 

 tal direction, and especially distinct in the deeper and softer stratum 

 of the cuticle. This special cuticular tunic of the duct is best ex- 

 hibited by treatment of recent specimens with solution of potass. 



The duct, on leaving the gland, follows a meandering, and often 

 rather spiral direction, through the areolse of the cutis,to the interval 

 between the papillae, where it becomes straight ; and it again assumes 

 a spiral course in perforating the cuticle (fig. 83). In the cutis its 

 curves are unequal, elongated, and wide ; but, in the cuticle, they 

 are commonly as close and regular as those of a common screw, the 

 form of which may be taken as a fair model of the ducts in this part. 

 It is not easy to explain the mode in which the spiral form is given 

 to the cuticular part of the duct. It has been imagined to result 

 from the condensation and flattening of the laminse of epidermis as 

 they approach the surface ; but the fact, that the spirals are not 

 closer near the orifice, is opposed to this notion. Their use, also, is 

 obscure ; for we cannot admit the validity of the ingenious idea that 

 the orifice of a spiral tube must be valvular, and, therefore, that they 

 mechanically resist the entrance of foreign substances. If they do 

 offer this opposition, it is only by the tortuosity resulting from the 

 spiral arrangement. The proper tunic of the duct in the substance 

 of the cuticle seems designed to keep it pervious, and may be that 



which gives it 

 its peculiar spiral 

 form. The aver- 

 age diameter of 

 the cavity of the 

 duct is r yVo inch 

 but, as it enters 

 the cuticle, it 

 usually becomes 

 wider. 



The last two 

 figures, as well as 

 some of the pre- 

 ceding ones, il- 

 lustrate the ana- 

 tomy of the 

 sweat-glands. 



Sebaceous glands, showing their size and relation to the hair-follicles : A The SebdCeOUS 



and B from the nose; c from the beard. In the latter the ctitis sends / j 

 down an investment to the hair -follicle. Magnified 18 diameters. fflttnOS are 



Fig. 92. 



