CEEEBEAL HEMORRHAGE. 167 



involving the third nerve of one side and the opposite half of the 

 body is characteristic of a lesion in the cms. This form of 

 paralysis may, however, be mimicked by multiple lesions else- 

 where, and also produced by pressure on the crus from without 

 by tumours. 



The substance of the pons is dense and resistant. This part 

 of the cerebro-spinal axis consists of interlacing fibres, some 

 longitudinal and some transverse, moreover, it is provided 

 with a central raphe. Haemorrhages are therefore small, and 

 may be confined to one side. The extravasated blood may travel 

 out in the middle cerebellar peduncle towards the cerebellum, 

 or as mentioned before, up in the lower portion of the crus. 

 Each half of the pons is supplied by median branches of the 

 basilar artery and by radicular branches which pass in along the 

 nerves. The radicular branch which is most liable to give way 

 is the branch to the large trunk of the fifth nerve. The proximity 

 to the pons of the ocular nuclei, the presence in it of the nuclei 

 of the fifth and seventh nerves as well as the fact that it transmits 

 the motor and sensory tracts account for the important symptoms 

 which are associated with pontine haemorrhage. Haemorrhages 

 which encroach on the dorsal part of the pons may rupture into 

 the fourth ventricle. 



Haemorrhage into the cerebellum is said to come from that 

 branch of the superior cerebellar artery which supplies the 

 dentate nucleus. The superior cerebellar artery is itself a branch 

 of the basilar. Cerebellar haemorrhage may rupture into the 

 fourth ventricle or spread over the surface of the cerebellum 

 beneath the pia and arachnoid. 



Haemorrhage into the ventricles is usually secondary to 

 haemorrhage into other parts of the brain. Occasionally primary 

 haemorrhage occurs, and may be derived from the arteries which 

 supply the wall of the ventricles. These arteries are mainly 

 branches of the posterior cerebral vessels, but the anterior 

 choroidal branches of the internal carotid also take part. It is 

 possible that ventricular haemorrhage is sometimes venous, being 

 derived from the striate veins. 



