522 Mil. youatt’s veterinary lectures. 
small enlargement is observed, and a gritty matter is not unfre- 
quently detected in it; and sometimes the vessels appear to be 
agglutinated together, and an ovoid tumour appears consider¬ 
ably larger than an almond. Here are two extraordinary speci¬ 
mens ; of the history of one I am ignorant—in the other speci¬ 
men each plexus, when first taken from the brain, weighed 
nearly ten drachms ; the ventricles were distended with serum, 
and the disease was marked by the principal symptoms of 
staggers. 
Use of the Ventricles. —Much dispute has arisen with regard 
to the use of the ventricles. Even in the healthy living animal 
they contain some portion of fluid. If the horse is destroyed and 
the cranium opened as speedily as possible, serum is found in 
the lateral ventricles. Some physiologists have contented them¬ 
selves with observing that the ventricles are merely cavities left 
in certain parts of the brain where irregular surfaces are opposed 
to each other; others as plausibly have imagined that they are 
formed by the foldings of the convolutions of the brain; while 
some have supposed that they were intended to preserve that full 
and perfect occupation of the cranial cavity which seems to be 
necessary to the safety of the brain in the natural motions of the 
animal. If a portion should be diseased and absorbed, the plexus 
choroides or the membrane of the ventricles may secrete a pro¬ 
portionate quantity of fluid; to which we may add these spaces 
left in the centre of the brain or filled only with fluid, are adapted 
to neutralize any concussion to which the brain may be exposed. 
The Cornua of the Ventricles. —The channel running along the 
floor of the ventricle terminates posteriorly in a blind pouch 
leading downwards towards the centre of the brain, and in which 
are found the pes hippocampi, and the acute termination of the 
plexus choroides—this is the superior cornu : the inferior cornu 
is more complicated; is takes a direction also towards the base 
of the brain, and is continued even into the mthmoidal ventricle, 
which I shall have presently to describe. From the winding 
course of both these canals, the name of cornua has been given 
to them. 
Tha Thalami Nervorum OpticorurU. —Having turned back the 
posterior angle of the fornix, and lifted the interposed membrane 
or veil which is stretched beneath it, we recognize two white pro¬ 
minent bodies; they are broad and somewhat divergent from 
each other posteriorly, but they approximate as they proceed for¬ 
wards, and gradually contract into two medullary bands, which 
wind round the crura cerebri, or accumulated mass of medullary 
matter below, and are the origins of the optic nerves: they will 
be more particularly described hcreaftci*, and they are now cur- 
