310 



Section IX. 

 NERVOUS SYSTEM. 



comprising the brain ; the spinal marrow 

 nerves; and the ganglia. 



OF THE BRAIN. 



THE brain is the soft white mass filling the cavity of the 

 cranium. 



Magnitude. — In no animal is the cranium so large, in relation 

 to the face, as in man ; consequently, in none other is the brain 

 (whose volume is always in uniformity with that of the cranium) 

 of such magnitude. In horses the brain is but small, compared 

 with the general bulk of the animal ; and though there exists 

 some difference in the dimensions, as well as form, of the heads 

 of horses of different breeds, they are too trifling, in an anatomi- 

 cal point of view, to merit notice here*. 



Division. — In the brain are distinguished three divisions, 

 though all three are continuous in one and the same substance : 

 t/ie cerebrum, so large that it occupies at least three-fourths of 

 the interior of the skull ; the cerebellum, or little brain ; and the 

 medulla oblongata. That portion of medullary substance which 

 extends from the brain through the whole length of the spinal 

 canal is called the medulla spinalis, or spinal marrow. 



Situation. — No viscus in the body is so well defended from 

 external injury as the brain : on every side it is enclosed by bony 

 walls, well constructed to make great resistance, and more espe- 

 cially so at those parts where external violence is likely to be 

 received. The interior of the skull is variously furrowed and 

 indented by the more projecting parts of the organ, to which, in 

 every particular, its figure is nicely adapted ; for it is by the 

 shape of the brain that that of the cranium is moulded, inasmuch 

 as the formation of the one precedes that of the other. The re- 

 lative situation of the divisions of the brain differs in the horse 

 from that of the corresponding parts of the brain of the human 



* " The brain of the shark does not weigh 3 ounces, although the animal 

 itself is generally 300 lbs. in weight. The brain of the sheep, with respect to 

 the whole weight of the body, bears the proportion of 1 to 150. In a dog 

 the proportion is less : it is as 1 to 100. As we ascend in the general scale 

 of rational beings, the magnitude of the brain bears an increased and 

 strongly marked proportion to the size of the system in general. In the 

 African, it is as 1 to 54. In an European, as 1 to the 50th part of the sys- 

 tern altogether." — Saumarbz'* System of Plii/siology. 



