148 ELEMENTS OF MAMMALIAN ANATOMY. 
and lungs from an injected cat, and carefully dissect away 
the fatty and connective tissues enveloping the vessels. 
The peripheral connection between the arteries and veins 
is by means of capillarics, which are microscopic vessels 
with an extremely thin wall composed of a single layer of 
epithelial cells. These capillaries are so abundant every- 
where in the flesh that a needle cannot be inserted without 
penetrating some. They form a kind of mesh or network, 
so that every cell may be supplied with oxygen and food 
and discharge its waste matter. All the blood carried to 
any portion of the body by the arteries is not returned by 
the veins, as a considerable amount of the plasma and some 
of the white corpuscles escape through the thin capillary 
walls and are returned to the circulation by a system of 
vessels called lymphatics (Fig. 80). 
PRACTICAL QUESTIONS AND SUGGESTIONS. 
1. What holds the heart in place? 
2. Draw the ventral aspect of the heart with the pericardium re- 
moved and label all features. 
3. When the heart is detached from the body, how do you distin- 
guish the dorsal from the ventral aspect? 
4. How many veins open into each auricle? 
5. What arteries lead from each ventricle? 
6. After dissecting write a detailed description of the valves of the 
heart. 
7. Describe the differences in the appearance of the walls of the 
aorta and vena cava. 
8. From your dissection write a description of the features seen in 
each cavity of the heart. 
g. Name the branches of the thoracic aorta in order. 
1o. Name the branches of the abdominal aorta and tell what organs 
each supplies. 
11. Draw the ceeliac axis and its branches throughout their course 
and label all parts. 
12. Show by a drawing the relations of the aorta and vene cave 
throughout. 
13. Make a diagrammatic cross-section of the neck, showing location 
of arteries and veins. 
