646 Chronic Dropsy of the Ventricles. 



ing at each heart beat aud in time may form a three coruered protrusion 2 mm. 

 in height. This often occurs in normal adult horses when adhesions may form with 

 the part on the opposite side. 



In the other domesticated animals the anatomical relations differ in important 

 details from those obtaining in the hor^e. In the dog the falx cerebri completely 

 separates the posterior portions of the hemispheres, the tentorium cereljeili is 

 completely ossified, and its edges closely cover the anterior pair of corpora quad- 

 rigemiua. In ruminants the medial surfaces of the hemispheres are in close con- 

 tact throughout their extent, the tentorium is purely fibrous and has a very wide 

 opening which allows the anterior third of the cerebellum to extend into the larger 

 cranial cavity, and the posterior portions of the hemispheres cover the cerebellum 

 to a considerable extent. In the pig the opening of the tentorium is somewhat 

 smaller than in cattle but it is sufficiently large to allow of somewhat extensive 

 contact between the cerebellum and the hemispheres. While in the dog the separa- 

 tion of the cerebrum from the eerelielhim is complete making protrusion impossible, 

 protrusion is prevented in ruminants and pigs owing to the fact that the space 

 lietween the cerebrum and cerebellum is too great. Swelling due to j>ressure (pro- 

 tiusion) is possilde then only in horses. From the anatomical point of view the 

 horse occupies the middle position. 



Under the action of repeated or long-continued pulsation 

 of the brain, or increased intracranial pressure, a large portion 

 of the occipital lobe is forced through the tentorial opening and 

 this causes more or less pronounced pressure upon the corpora 

 quadrigeniina lying below. The compressed corpora assist in 

 the compression of the aqueduct, thus hindering the outflow of 

 the fluid from the ventricles (lateral) into the fourth ventricle 

 and thence into tlie sub-arachnoid spaces. Once this passage is 

 obstructed the forced collection of cerebral fluid in the ventri- 

 cles causes a rise in the intracranial pressure and this causes 

 greater protrusion of the occipital lobes and still further com- 

 pression of the aqueduct. Once the process is started recovery 

 is impossil)le, the condition becomes aggravated with intermis- 

 sions, and gradually in most cases leads to complete occlusion 

 of the aqueduct of Sylvius. 



All factors which cause a rise of intracranial pressure 

 either for any length of time or repeatedly iivdj set up chronic 

 dropsy of the ventricles. In this connection special mention 

 should be made of acute meningitis, frequently repeated or per- 

 sistent cerebral hyperemia, acute encephalitis, tumors of the 

 brain, etc. 



Not rarely the disease appears to be primary and makes its 

 appearance without any of the above-mentioned diseases being 

 in existence (primary internal hydrocephalus). In such cases 

 the excessive pulsation of the brain is due to various sensory 

 impressions, excessive work, labored respiration, variations of 

 temperature, poisons, etc. As a rule no increase of blood pres- 

 sure can be demonstrated. 



In no instance in his accurate investigations did Dexler find any histological 

 alterations in the venous plexuses, choroid plexus or ependyma lining the ventricles. 

 He therefore thinks it probable that the normal quantity of fluid escapes from the 

 plexuses and that the congestion is not therefore })roduced by an excess of fluid 

 escaping from the veins. If this were true, as cannot be shown in cases following 

 acute inflammatory processes, there would be no pronounced protrusion of the 

 occipital lobes or compression of the aqueduct. 



