STRUCTURE OF THE LARGER BLOOD-VESSELS. 10 1 ; 



LESSON XXII. 



STRUCTURE OF THE LARGER BLOOD-VESSELS. 



1. SECTIONS of a medium-sized peripheral artery and vein, e.g. popliteal or 

 radial. In this preparation the limits of the vascular coats can be well seen 

 and also the differences which they present in the arteries and veins respec- 

 tively. The sections may be stained with hsematoxylin and mounted in 

 Canada balsam. 



2. Mount in Canada balsam a thin slice cut from the inner surface of an 

 artery which, after having been cut open longitudinally and washed with 

 distilled water, has been rinsed with nitrate of silver solution and exposed to 

 the light in spirit. This preparation will show the outlines of the eiido- 

 thelium-cells which line the vessel. 



3. A piece of an artery which has been macerated for some days in 30 per 

 cent, alcohol (1 part rectified spirit to two parts water) is to be teased so as 

 to isolate some of the muscular cells of the middle coat and portions of the 

 elastic layers (networks and fenestrated membranes) of the inner and middle 

 coats. The tissue may be stained cautiously with diluted haematoxylin, and 

 glycerine afterwards added. The muscular cells are recognisable by their 

 irregular outline and long rod-shaped nucleus. Sketch one or two and also a 

 piece of fenestrated membrane. 



4. Transverse sections of aorta and carotid. Notice the differences in struc- 

 ture between these and the section of the smaller artery. 



5. Transverse section of vena cava inferior. Notice the comparatively 

 thin layer of circular muscle, and outside this the thick layer of longitudinal 

 muscular bundles. 



Make sketches from 1, 4, and 5 under a low power, from 2 and 3 under 

 a high power. 



An artery is usually described as being composed of three coats, 

 an inner or elastic, a middle or muscular, and an external or areolar 

 (fig. 130, b, c, d). It would, however, be more correct to describe the 

 wall of an artery as being composed of muscular and elastic tissue 

 lined internally by a pavement-epithelium (endothelium) and strength- 

 ened externally by a layer of connective tissue. For the present, how- 

 ever, we may adhere to the generally received mode of description. 

 The inner coat of an artery is composed of two principal layers. The 

 inner one is a thin layer of pavement-epithelium or endothelium, the cells 

 of which are somewhat elongated in the direction of the axis of the 

 vessel (fig. 131), and form a smooth lining to the tube. After death 



