LESSON XII. 



STRUCTURE AND PROPERTIES OF BLOOD- 

 VESSELS. 



A. THE LARGER ARTERIES. 



1. Cut transverse and longitudinal sections of a _ 

 small piece of the aorta or carotid artery of a 

 dog (or other animal), which has been preserved 

 in potassium bichromate 1 p. c. ; stain with picro- 

 carmine. Note 



a. The thin inner coat thrown into longitudinal 

 folds by the contraction of 



b. The much thicker middle coat, consisting 

 of alternating layers of elastic and circularly 

 arranged muscular tissue. Both of these are 

 stained of a yellower tint than the white 

 fibrous tissue. The disposition and relative 

 amount of the elastic and muscular tissue 

 will be found to vary much in different 

 arteries. 



c. The external coat (tunica adventitia), con- 

 sisting mainly of white fibrous connective 



