304 ANATOMY AND PHYSIOLOGY 



subsequently upon the bones of the skull. It is very likely to occur in 

 children who have rachitis, or " rickets." 



By a foramen in the arachnoid membrane, the ventricular cavities and 

 central canal communicate with the subarachnoid space, allowing cerebro- 

 spinal fluid to flow through all of these parts. (See p. 281), Arachnoid. 



Surgical note. Because of this, the operation of lumffar puncture may 

 relieve the pressure of hydrocephalus. 



A similarity in structure and arrangement of parts is plainly evident in 

 the brain and spinal cord. Recall the cord a collection of nerve fibers, 



FIG. 195. THE VENTRICLES, SHOWING BASAL GANGLIA IN THE FLOOR OF THE 

 LATERAL VENTRICLES. (Hirschfeld and 



a, Anterior portion of corpus callosum; ft, caudate nucleus; c, location of lentiform 

 nucleus; d, optic thalamus; h, i, quadrigeminal bodies; g, third ventricle; o, fourth 

 ventricle; p, medulla. The fifth ventricle is in front of e. 



the greater number running up or down, but with many passing from one 

 side to the other; a central canal surrounded by collections of "gray matter"; 

 two lateral halves connected by transverse commissural fibers. 



These parts may all be traced in the brain. The central canal extends 

 through the medulla and pons into the cerebrum, expanding into a general 

 ventricular cavity. Gray matter (ganglia) lies close to this canal, even pro- 

 jecting into it. The white fibers are here, but they diverge on every side, and 

 many take new directions; also the halves of the brain are connected by 

 transverse (commissural) fibers (the corpus callosum). The brain has one 



