128 ELEMENTARY PHYSIOLOGY. [XII. 



and constituting the simplest form of a 

 tunica adventitia. 



d. The connection of some of the processes of 

 the connective-tissue corpuscles with the ca- 

 pillary walls. 



2. Remove a small portion of pia mater from a per- 

 fectly fresh brain of a chloroformed cat or dog 

 allowed slowly to bleed to death, and spread it 

 out carefully in normal saline solution, washing 

 it gently with the same, and mount. Note 



a. The capillaries, with their nuclei bulging into 

 the channels. 



b. The small arteries, their scanty external con- 

 nective-tissue coat or adventitia, and the 

 indications of their muscular coat composed 

 of a single layer of fibres wrapped round the 

 intima. 



c. The small veins generally filled with blood- 

 corpuscles, with their muscular coat absent 

 or developed only to a slight degree. 



3. Gently irrigate with acetic acid 1 p. c. Note 



a. In the capillaries, the more distinct nuclei. 



b. In the small arteries, 



(a) The fusiform cells and nuclei of the 

 adventitia, arranged longitudinally, with 

 elastic fibres. 



(ft) The nuclei of the muscular coat ar- 

 ranged transversely. By watching the 



