392 



HISTOLOGY 



entirely separate structures. Occasionally a sweat gland opens into the 

 sheath of a hair near its outlet. Each hair consists of a papilla, bulb and 

 shaft, together with sheaths around the root, namely an inner and outer 

 epithelial sheath and, external to these, a connective tissue sheath. 

 These structures, together with the arrector pili muscle which is inserted 

 into the connective tissue sheath, are indicated in Fig. 398, but they are 



Shaft of a hair. --- 

 Stratum corneum. 



Stratum germinativum. 'V~ 

 Corium. - i_- 



(': ft 



Sebaceous gland. 



M. arrector pili. 



Sweat gland. 



Outer epithelial sheath. 



Inner epithelial sheath. - 

 Medulla. 



Cortex. 

 Conn, tissue sheath. 



Bulb. 

 Papilla. 



Stratum subcutaneum. 

 Epicranial tendon. --- 



FIG. 398. THICK SECTION OF THE HUMAN SCALP. X 20. . 



shown in detail in the longitudinal section, Fig. 399, and in the transverse 

 sections, Figs. 401-405. They may be described as follows: 



The connective tissue sheath, derived from the corium, is found around 

 the roots of the coarser hairs, but is absent from the lanugo. It may be 

 subdivided into three concentric layers. The outermost consists of loose 

 connective tissue with longitudinal fibers, and contains elastic tissue and 

 numerous vessels and nerves. The middle layer, which is thicker, consists 

 of circular bundles of connective tissue without elastic fibers. The inner 



