Lesson xxxix.] OF THE BLOOD. 29-7 



their bnmches, perhaps, more numerous. Their 

 coats are much weaker and more slender than 

 those of the arteries. They are furnished with 

 several vdlves, contrived in such a manner as to 

 permit the Blood 10 pass freely from the smaller 

 into the larger branches, but to stop its retrogres- 

 sion. They neither throb nor beat. Their begin- 

 nings form continued pipes with the extremities of 

 the arteries, or arise horn some gland or recep- 

 tacle where the arteries terminate. All the veins 

 in the lungs, from their capillary beginnings grow- 

 ing still larger, unite at last and dischaige their 

 Blood into the left auricle of the heart: and all 

 those in the rest of the body empty themselves in 

 like manner, into the vena cava, which opens into 

 the right auricle of the heart. 



The nerves deduce their origin from the brain, 

 or its appendages, in several pairs, ofacylindric 

 form, (like so many skeins of thread with their 

 respective sheaths;, which in their progress de- 

 crease by endless divisions and subdivisions, until 

 at last they spread themselves into a texture of 

 filaments, so slender, and so closely interwoven 

 with each other over the whole body, that the point 

 of a needle can hardly be put upon any part of it, 

 without touching the delicate branch of some 

 nerve. 



It has been found by many trials, that when an 

 artery is laid bare, and a ligature made upon it, if 

 it be opened with a lancet between the ligature 

 and the heart, the Blood will rush out with great 

 violence j and a rapid, jerking stream will coa- 

 O 5 



