26 THE PHILOSOPHY 



STRUCTURE and ORGANS. 



IN all organized bodies, a fimilarity of flrudlure Teems to 

 be iiuavoidable. The bodies of men and quadrupeds conlifl 

 of a feries of connected bones, which run from the head to 

 the rump. This feries is known by the name of the back- 

 bone, from each fide of which, a number of arched bones pro- 

 ceed. Some of thefe join the breaft-bone by means of car- 

 tilages, and form a vaulted cavity, which contains and de- 

 fends the heart, and other vifcera proper to the cheft. The 

 bones of the pelvis, and of the four extremities, are joined to 

 the back-bones by articulations and membranes. By the 

 fame contrivance, the cranium is fixed to the upper end of 

 the back bones. Into different procefTes and portions of all 

 thefe bones, a great number of mufcles, or bundles of flefliy 

 ^bres are inferted. Thefe mufcles are the inffcruments which 

 give rife to all the varieties of animal motion. The bones of 

 the head, or cranium, contain the brain and cerebellum, a 

 prolongation of which runs through the whole extent of the 

 canal in the back-bone, and is known by the iQvin Jpitial mar^ 

 row. From the brain and fpinal marrow proceed all the 

 nerves, or inflruments of lenfation. Thefe nerves, the ram- 

 ifications of which are infinitely various and minute, are dif- 

 tributed upon the heart, lungs, blood vefTels, bowels, and 

 mufcles, till they terminate on the flcin, or external covering 

 of the body. The heart is the fountain, or general recepta- 

 cle of the blood. The contraction of the heart propels the 

 blood through the arteries, which are likewife difl:ributed,by 

 numerous and complicated ramifications, over every part of 

 the body, and terminate in the veins, which again colledl the 

 whole arterial blood into one cavity^ and reconvey it to the 

 heart. This circulatory procefs goes on during life. 



Befide the organs already mentioned, there are others, 

 termed /t'cretory, becaufe they feparate peculiar fluids froni 



