By this term is meant bleeding in the substance of the brain. The blood, which may be large or small in quantity, pushes aside the brain substance, tearing for itself a cavity where it coagulates. With the doubtful exception of certain diseases of the blood, where the haemorrhage may possibly be by diapedesis, there is always rupture of one or more vessels.

In a previous page reference has been made to the two orders of cerebral arteries, and the difference in the circumstances of haemorrhages from these is such that we must consider them separately here.