202 THE VITAL FUNCTIONS. 



cent bones. Grooves are formed in many of the bones, 

 where arteries are lodged, with the evident intention of af- 

 fording them a more secure passage. Thus, the principal 

 arteries which supjily the muscles of the chest, proceed 

 alonn- the lower ed";es of the ribs, in deep furrows formed 

 for their protection. Arteries are often still more effectu- 

 ally guarded against injury or obstruction by passing through 

 complete tubes of solid bone. An instance occurs in the ar- 

 teries supplying the teeth, which pass along a channel in the 

 lower jaw, excavated througli tlie whole length of the bone. 

 The aorta in fishes, after having supplied arteries to the vis- 

 cera of the abdomen, is continued to the tail, and passes 

 through a channel, formed by bony processes from the ver- 

 tebra; and the same kind of protection is aflbrded to the 

 corresponding artery in the Cetacea. In the fore leg of the 

 Lion, which is employed in actions of prodigious strength, 

 the artery, without some especial provision, would have 

 been in danger of being compressed by the violent contrac- 

 tions of the muscles: in order, therefore, to guard against 

 this inconvenience, it is made to pass through a perforation 

 in the bone itself, where it is completely secure from pres- 



sure.* 



The energy of every function is regulated in a great mea- 

 sure by the quantity of blood which the organs exercising 

 that function receive. The muscles employed in the most 

 vigorous actions are always found to receive the largest 

 share of blood. It is commonly observed that the right 

 fore leg of quadrupeds, as well as the right arm in man, is 

 stronger than the left. Much of this superior strength is, 

 no doubt, the result of education; the right arm being habi- 

 tually more used than the left. But still the different mode 

 in which the arteries are distributed to the two arms consti- 

 tutes a natural source of inequality. The artery supplying 

 the risht arm willi blood is the first which arises from the 



• In like manner the coffin bone of the Horse is perforated for tlie safe 

 conveyance of tlie arteries going to the foot. 



