214 ANATOMY AND PHYSIOLOGY FOR NURSES 



they are pyramidal in form, and the motor fibers of each 

 side decussate with one another. This is apparent from 

 the fact that in conditions in which one side of the brain 

 is affected, loss of power is manifested on the opposite 

 side of the body. The decussation takes place only be- 

 tween' the inner fibers of the pyramids, and also from the 

 lateral columns of the cord. 



The olivary bodies are situated on the outer side of the 

 pyramids. The restiform bodies are on the outer side 

 of and behind the olivary bodies. They diverge from each 

 other and pass into the cerebellum. 



The Arterial Supply to the Brain. As was stated 

 in a previous chapter, the circle of Willis is formed by 

 the two internal carotids and the two vertebral arteries. 



The internal carotid artery enters the skull through a 

 canal in the petrous portion of the temporal bone; it 

 becomes very tortuous, and passes by the side of the 

 sphenoid bone, giving off the ophthalmic artery. It 

 divides into the anterior and middle cerebral arteries, 

 which supply the anterior and middle cerebral lobes of the 

 brain. (This artery has been more fully considered in the 

 chapter on the Circulatory System.) 



The anterior cerebral artery distributes branches in all 

 directions. It runs forward upon the lower surface of the 

 brain, and then curves round in the front of the corpus 

 callosum to pass backward along the dorsal surface of this 

 structure. It is connected, soon after its origin, with the 

 artery of the opposite side by a communicating branch. 

 The middle cerebral artery runs outward along the fissure of 

 Sylvius, distributing large branches to the anterior and 

 middle lobes of the brain. 



The vertebral artery, after winding backward along the 

 arch of the atlas, enters the skull through the foramen 

 magnum, and unites with its fellow at the lower border of 

 the pons, to form the basilar artery; it then divides at the 



