CEPHALO-RACHIDIAN LIQUID 547 



are arranged in longitudinal bands. This membrane lines the anterior 

 fissure and a portion of the posterior fissure of the cord. At the fora- 

 mina of exit of the cranial and the spinal nerves, the fibrous structure of 

 the pia mater becomes continuous with the nerve-sheaths. 



Between the anterior and posterior roots of the spinal nerves, on 

 either side of the cord, is a narrow ligamentous band, the ligamentum 

 denticulatum, which assists in holding the cord in place. This extends 

 from the foramen magnum to the terminal filament of the cord, and 

 is attached internally to the pia mater, and externally, to the dura 

 mater. " 



Cephalo-rachidian Liquid. The greatest part of the liquid in the 

 cranium and in the spinal canal is contained in the subarachnoid space. 

 The ventricles of the encephalon are in communication with the central 

 canal of the cord, and also are connected with the general subarachnoid 

 space by a narrow triangular orifice at the inferior angle of the fourth 

 ventricle. By this arrangement the liquid in the ventricles of the 

 encephalon and in the central canal of the cord communicates with the 

 liquid surrounding the cerebro-spinal axis, and the pressure on these 

 parts is equalized. 



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

 mechanical, and its properties and composition have no very definite 

 physiological significance. Its quantity has been estimated in the human 

 subject at about two fluidounces (60 cubic centimeters); but this was the 

 smallest quantity obtained by placing the subject upright, making an 

 opening in the lumbar region and a counter-opening in the head to 

 admit the pressure of the atmosphere (Magendie). The exact quantity 

 in the living subject could hardly be estimated in this way ; and it is 

 difficult, indeed, to see how anything more than a roughly approximate 

 idea could be obtained. The quantity indicated probably does not 

 represent all the liquid contained in the ventricles and in the subarach- 

 noid space ; but as it is the most definite estimate that has been made, it 

 is given as an approximation. It is probable that the quantity is subject 

 to considerable variations. 



The general properties and composition of the cephalo-rachidian 

 liquid are in brief the following : It is transparent and colorless, free 

 from viscidity, 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 proportion of water (981 to 985 parts per thousand), 

 a considerable quantity of sodium chloride, a trace of potassium chloride, 

 sulphates, carbonates and alkaline and earthy phosphates. In addition 

 it contains traces of urea, glucose, sodium lactate, fatty matter, choles- 

 terin and albumin. 



