DIRECTIONS FOE LABORATORY WORK 793 



differences in color of hair. Sketch under h.p. a portion of the shaft 

 (204). 



(2) In a stained vertical section of the scalp examine, under the 

 low power, a hair follicle with its included hair in longitudinal section. 

 Note: (a) hair papilla; (b) hair bulb (pigmented?) ; (c) hair root; 

 (d) epidermal root sheath; (e) arrector pili muscle; (f) sebaceous 

 gland. Sketch (205). Make h.p. sketch (206) of the hair and its 

 follicle, cut longitudinally, at the level of the sebaceous gland (about 

 the middle third of the root), noting the several layers of the inner 

 and outer root sheaths (the epidermal sheath), and of the dermal sheath. 

 What is the function of the arrectores pilorum muscles? Make h.p. 

 sketch (207) of the region of transition from root and follicle to the 

 hair bulb. 



(3) Sketch h.p. (208) a transverse section of a hair follicle at or 

 near the level of the middle third, showing the several layers of the 

 follicle as above. What layers are homologous in hair follicle and skin? 

 Explain the homologies in terms of development. Explain the cause of 

 the curling of certain types of hair. 



(E) SEBACEOUS GLAND. 



(1) Study a sebaceous gland in a stained vertical section of the 

 scalp. Note its relation to the hair follicle. Note also its duct and 

 saccules. Sketch l.p. (209). Make h.p. sketches (210 a, b, c) of cells 

 of the sebaceous gland at three successive stages of their metamorphosis 

 into the sebum 'secretion'. How many glands to a hair follicle? 



(F) THE BLOOD SUPPLY. 



(1) Study in stained section injected specimens of skin and scalp. 

 Sketch (211). Note the precise location of the several vascular plexuses 

 of the derma and the tela stibcutanea ; and the blood supply of the sweat 

 glands, hair follicles, sebaceous glands, and the fat lobules of the tela. 



XIII. THE RESPIRATORY SYSTEM 



(A) THE NASAL CAVITY. 



(1) Study in a stained section the lining mucous membrane of the 

 vestibule. Note transition from external skin to internal mucous mem- 

 brane ; note, also the vibrissae and the associated sebaceous glands. Make 

 h.p. sketch of a narrow segment (212). 



(2) Study mucosa of respiratory portion ( Schneiderian membrane). 



