281 



^ 4. Distrihution of Blood-vessels. 



In the distribution of the arteries in the animal 

 system, we meet with numberless proofs of wise 

 and provident arrangement. The great trunks 

 of both arteries and veins, which carry on the 

 circulation in the limbs, are conducted always 

 on the interior sides, and along the interior 

 angles of the joints, and generally seek the 

 protection of the adjacent bones. Grooves are 

 formed in many of the bones, where arteries 

 are lodged, with the evident intention of afford- 

 ing them a more secure passage. Thus the 

 principal arteries which supply the muscles of 

 the chest, proceed along the lower edges of 

 the ribs, in deep furrows formed for their pro- 

 tection. Arteries are often still more effectually 

 guarded against injury or obstruction by pass- 

 ing through complete tubes of solid bone. An 

 instance occurs in the arteries supplying the 

 teeth, which pass along a channel in the lower 

 jaw, exca¥ated through the whole length of the 

 bone. The aorta in fishes, after having supplied 

 arteries to the viscera of the abdomen, is con- 

 tinued to the tail, and passes through a channel, 

 formed by bony processes from the vertebrae ; 

 and the same kind of protection is afforded 

 to the corresponding artery in the Cetacea. In 



