32 SURGICAL APPLIED ANATOMY. [Chap. in. 



yielding structure, and does not entirely fill the 

 cranial cavity, it may, as it were, be thrown about 

 within the skull, and be damage I by collision with its 

 walls. Of the exact mechanism of concussion or 

 shaking of the brain little is known, and it cannot be 

 said that experiments, such as those of M. Gama, 

 with a bulb of isinglass within a glass matrass, tend to 

 throw much light upon the subject. In contusion or 

 bruising of the brain, it is noticed that the lesion is 

 very much more frequently situate on the under sur- 

 face, both as regards the cerebrum and cerebellum, 

 than on any other part (Prescott Hewett). To this 

 statement, however, there is the striking exception 

 that those parts of the base of the cerebrum that 

 rest upon the large basal collection of the cerebro- 

 spinal fluid are the least often contused. These parts 

 include the medulla, the pons, and the interpeduncular 

 space. 



The brain is very lavishly supplied with blood- 

 vessels. The main arterial trunks (vertebral and 

 internal carotid) are both rendered tortuous before 

 entering the skull, with the object probably of 

 diminishing the effects of the heart systole upon the 

 brain. On entering, they are almost immediately 

 blended into an anastomosing circle (circle of Willis), 

 which has the effect of equalising the cerebral circu- 

 lation. Ligature of one common carotid may produce 

 no effect upon the brain, although the mortality after 

 this operation is mainly due to cerebral complications. 

 One carotid and the two vertebrals would appear to be 

 able to bring enough blood to the brain, which blood 

 will be as evenly distributed as hitherto by the circle 

 of Willis. Both common carotids have been ligatured, 

 or one carotid has been secured, when its fellow of the 

 opposite side has been occluded by disease, and 110 

 marked cerebral disturbances have followed. In no 

 case, however, has the patient recovered when the 



