134 



SPINAL COLUMN. 



strangest. Who would suppose these to be the materials 

 which form the noble organ of thought ! Does the brain, 

 like the spinal marrow, receive nerves from other parts? 

 Dr. B. Yes ; we find eleven pairs of nerves con- 

 nected with the base of the brain, which supply the or- 

 gans of sense, the muscles of the face, and the muscles 

 concerned in respiration. Coming from these parts, 

 they pass through holes in the bony case of the brain, 

 and run along its base, till they are finally lost in the ob- 

 long marrow. 



Emily. You observed just now, that the spinal mar- 

 row is enclosed in a bony case the spine or back bone, 

 I believe. I do not clearly perceive how this can be, for 

 I thought that the spine was solid bone. 



Dr. B. I will describe it then, a little more definite- 

 ly. The back-bone, spine, spinal column, vertebral co- 

 lumn for it is designated by all these names is not 

 formed by a single bone, but by 

 twenty four small bones piled upon 

 each other. Each bone, as you 

 will see by this figure, is composed 

 of its body and processes ; the first 

 is thick, nearly cylindrical in shape, 

 and its broad flat terminating surfa- 

 ces connect it with the bones above 

 and below. The processes are those 

 smaller portions of bones, proceed- 

 ing from different portions of the 

 body in pairs. Two pairs serve to 

 interlock and bind firmly together, 

 each bone to its neighbour ; while the other pair, after 

 proceeding a short distance from the posterior portion of 

 the body, meet at an acute angle. Now when the bones 

 are applied to each other, the space thus enclosed by 

 these posterior processes, will form a continuous canal 

 from beginning to end. 



Emily. -And it is in this canal then, that the spinal 

 marrow is lodged. But why could not the spine have 



