792 DIRECTIONS FOR LABORATORY WORK 



ences between thick and thin skin? Between thin skin and the mucous 

 membrane lining the mouth? Note the delicate hairs. 



(3) Make h.p. sketches (198, a, b, c) from different portions of a 

 section through the head of a 20-mm. pig fetus, illustrating three 

 earlier stages in the development of skin : one consisting of a single 

 layer of cells (with superjacent periderm or epitrichium), one of two 

 or three layers, and one of a larger number of layers. 



(4) Compare sections of thin skin of: (a) dark negro; (b) light 

 mulatto; (c) brunette; (d) blond. Note quantity and distribution of 

 the pigment (melanin) granules in the several specimens of skin. 



(B) SWEAT GLANDS (Sudoriparous glands}. 



(1) In a stained vertical section of skin identify and study a sweat 

 gland (complete if possible). Note: (a) its duct (excretory) including 

 the spiral 'mouth' within the epidermis; (b) its coiled fundus (secre- 

 tory). Under h.p. draw a cross-section of the dermal (or subcutaneous) 

 duct and fundus (199). Note the longitudinally disposed smooth mus- 

 cle cells between the secretory cells of the fundus and the membrana 

 propria. 



(C) THE NAILS (Unguis; Onyx). 



(1) Examine a finger-nail and note: (a) body; (b) root; (c) lun- 

 ula; (d) nail sulcus; (e) nail fold or vallum; (f) eponychium; (g) 

 hyponychium. Sketch (200). Explain the opacity and color of the 

 lunula. 



(2) Study l.p., a stained transverse section of the finger tip includ- 

 ing the nail. Note the homologous layers of nail and adjacent skin. 

 What differences obtain? What layer of the epidermis does the nail 

 body represent ? How does the pars papillare differ in the two regions ? 

 Sketch (201). 



(3) Make l.p. sketch (202) of a stained vertical longitudinal section 

 of the unguinal phalanx. Note nail matrix and nail bed. What is the 

 epidermal homologue of the nail matrix? The relation of the matrix 

 to the lunula? Sketch (203) h.p. a small area through the body of the 

 nail including its corium. 



(D) THE HAIR (Pilus; Thrix). 



(1) Mount in water under cover-glass a freshly extracted hair. 

 Note: (a) hair bulb; (b) root (radix); (c) shaft (scapus) ; (d) me- 

 dulla; (e) cortex; (f) pigment granules; and (g) cuticle. Explain 



