PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 589 



As far as is known, the office of the cephalo-rachidian fluid is simply 

 mechanical, and its properties and composition have no very definite physio- 

 logical significance. Its quantity was estimated by Magendie, in the human 

 subject, at about two fluidounces (60 c. c.) ; but this was the smallest quan- 

 tity obtained by placing the subject upright, making an opening in the lum- 

 bar region and a counter-opening in the head to admit the pressure of the 

 atmosphere. The exact quantity in the living subject could hardly be esti- 

 mated in this way ; and it is difficult, indeed, to see how any thing more than 

 a foughly approximate idea could be obtained. The quantity obtained by 

 Magendie probably does not represent all the liquid contained in the ventri- 

 cles and in the subarachnoid space, but it is 4he most definite estimate that 

 has been given. 



The general properties and composition of the cephalo-rachidian fluid 

 are in brief the following : It is transparent and colorless, free from viscid- 

 ity, of a distinctly saline taste, an alkaline reaction, and it resists putrefaction 

 for a long time. It is not affected by heat or acids. It contains a large pro- 

 portion of water (981 to 985 parts per thousand), a considerable quantity of 

 sodium chloride, a trace of potassium chloride, sulphates, carbonates and alka- 

 line and earthy phosphates. In addition it contains traces of urea, glucose, 

 sodium lactate, fatty matter, cholesterine and albumen. 



As a summary of the office of the cephalo-rachidian fluid, it may be 

 stated in general terms that it serves to protect the cerebro-spinal axis, 

 chiefly by equalization of the pressure in the varying condition of the blood- 

 vessels, filling the space between the centres and the bony cavities in which 

 they are contained. That the blood-vessels of the cerebro-spinal axis are sub- 

 ject to variations in tension, is readily shown by introducing a canula into 

 the subarachnoid space, when the jet of fluid discharged will be increased 

 with every violent muscular effort. The pressure of the fluid, in this in- 

 stance, could be affected only through the blood-vessels. 



PHYSIOLOGICAL ANATOMY OF THE SPINAL CORD. 



The spinal cord, with its membranes, the roots of the spinal nerves and 

 the surrounding liquid, occupies the spinal canal and is continuous with the 

 encephalon. Its length is fifteen to eighteen inches (38'1 to 45'7 centi- 

 metres) and its weight is about an ounce and a half (42'5 grammes). Its 

 general form is cylindrical, but it is slightly flattened in certain portions. 

 It extends from the foramen magnum to the lower border of the body of the 

 first lumbar vertebra. It presents, at the origin of the brachial nerves, an 

 elongated ovoid enlargement flattened antero posteriorly, and a correspond- 

 ing enlargement at the origin of the nerves which supply the lower extremi- 

 ties. It terminates below in a slender, gray filament, called the filum termi- 

 nale. The acral and coccygeal nerves, after their origin from the lower 

 portion of the cord, pass downward to emerge by the sacral foramina, and 

 they form what is known as the cauda equina. The substance of the cord 

 is composed of white and gray matter, the white matter being external. 

 The inferior, pointed termination of the cord consists entirely of gray matter. 



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