LESSON XVII. 



STRUCTURE OF BLOOD VESSELS. 

 CIRCULATION. INFLAMMATION. 



1. Large Arteries and Veins. Transverse 

 sections of thoracic aorta, carotid artery, and jugular 

 vein of dog (potassium bichromate 2 p.c.). Stain 

 with hsematoxylin and eosin (Less. v. 8), or with 

 hsematoxylin and picric acid. Mount together. 



a. Note in the aorta the inner coat, consisting 

 of an epithelioid lining shown chiefly by the nuclei, 

 and of a thin layer of elastic tissue with a small 

 amount of white fibrous tissue. The elastic tissue 

 shows chiefly as transversely cut fibres. 



The thick middle or muscular coat consisting of 

 bundles of smooth muscle and elastic fibres circularly 

 arranged in alternating layers. 



The outer coat, much thinner than the middle, 

 consisting of white fibrous tissue and of elastic tissue ; 

 most of the fibres of the elastic tissue are cut trans- 

 versely, they diminish in number in passing outwards. 



