54 The EncepJialon 



explained on p. 348. At the autopsy of such a case the arteries are 

 found diseased, and therefore weakened, the left ventricle being hyper- 

 trophied and therefore strengthened. 



Sometimes Nature hoists a danger-signal before the final apoplectic 

 fit occurs : such signals are headaches, epistaxis, and retinal haemor- 

 rhages which may be seen by ophthalmic examination. 



The internal capsule consists of fibres from both the motor (crusta) 

 and sensory (tegmentum) tracts of the crus, which hold the cortex in 

 direct communication with the cord. Thus damage to the anterior 

 part of the internal capsule causes motor paralysis, and to the 

 posterior part loss of sensation, upon the opposite side of the body. 

 The paralysis in the former case is diffuse, and not confined to a group 

 of muscles as in the case of a cortical lesion. 



The optic thalami lie behind the corpora striata, and nearer to the 

 middle line, being separated from each other only by the narrow third 

 ventricle. They receive fibres from the sensory tracts of the cord, which 

 reach them through the cerebral aspect of the crura the tegmenta ; 

 each thalamus sends fibres into all parts of the cerebral cortex, and 

 these constitute the corona radiata. 



The crura cerebri consist of fibres ascending from the cord, those 

 from its motor tracts being gathered in the superficial part, the crusta, 

 and those from the sensory tracts in the deeper part, the tegmcntum. 

 The former set pass, for the most part, through the corpus striatum and 

 internal capsule, to the motor area, by the corona radiata, whilst the 

 tegmental set pass to the thalamus and through the cororja radiata 

 to the sensory area of the cerebral cortex. Between crusta and teg- 

 mentum is a mass of grey cells, locus niger, through which the fibres 

 of the third nerve pass. Between the crura, as they diverge at the 

 front of the pons Varolii, is the posterior perforated space, by which a 

 group of vessels from the posterior cerebral arteiy reach the thalamus. 

 The tegmental fibres descend in the cord, in the direct (Tiirck's) and 

 in the crossed pyramidal tracts. 



Hcemorrhagcinto the crus cerebri causes hemiplegia on the opposite 

 side of the body, and of the third nerve upon the side of the lesion, 

 provided that the inner fibres are involved. 



Pons Varolii. As the fibres descend from the crura to the medulla 

 they pass under cover of the middle commissure of the cerebellar 

 hemispheres, and, though the term ' pons' should only apply to the 

 bridging cerebellar fibres, still the word is usually applied to the 

 entire mass of the tuber annulare. As the fibres from both crura 

 descend through the pons, cerebral ha-morrhage in its substance 

 generally causes motor paralysis on both sides of the body, coma 

 following immediately, and death not being long delayed. But when 

 the haemorrhage is limited to one side there is hemiplegia upon the 

 opposite side of the body, but paralysis of fifth, sixth, and seventh 

 nerves upon the same side. 



