AND PHYSIOLOGY. 



217 



Fig. 220. 



378. The Veins — Their Coats— Their Volume.— The Veins 

 carry the blood from all parts of the body to the heart. Like 

 the arteries, they have three coats, and the larger veins follow 

 the same general course as the large arteries. The smaller 

 veins, however, are much more numerous than the smaller ar- 

 teries, and are most abundant just beneath the skin. The 

 whole volume of the veins may be regarded as a large cone, 

 with the base at the surface of the body ,and the apex at the 

 heart, so that in these vessels the blood is continually flowing 

 faster and faster, in consequence of the fluid coming into a 

 larger channel from small extremities, while the reverse hap- 

 pens in the arteries. The veins are much thinner in struc- 

 ture than the arteries, so that after death they most usually 

 collapse. (See Fig. 218, p. 215.) 



379. Location of the larg- 

 er Veins — Sinuses— As al- 

 ready mentioned, the larger 

 veins usually lie near the 

 larger arteries. Both also 

 frequently have the same 

 names. But there are sev- 

 eral remarkable exceptions to 

 this, as in the vessels of the 

 brain. Here are but few 

 veins, but several sinuses or 

 channels. These are canals 

 excavated in the dura mater 

 of the brain with this mem- 

 brane for an outer coat, and 

 the serous layer of the true 



veins for an inner coat. These simises of the Base of the skuii. i, 



run in different directions On Ophthalmic Veins. 2, Cavernous Sinus. 



3, Circular. 4, 6, Inferior Petrosal. 5, 9, 

 the inside Of the Skull, and Occipital Sinuses. 7, Internal Jugular 



Vein. 



37S. What course does the blood take in the veins ? Give the coa:s of the veins. 

 What is the relative proportion of small veins and small arteries? What is said of their 

 aggregate volume? 379 Where are the larger veins usually found ? What are Sinuses, 

 and where are they found ? 



