72 VETERINAEY STATE BOAED 



Name the principal parts of the brain. 



Cerebrum, cerebellum, the isthmus, and medulla oblongata. 



Describe the island of Reil. 



The island of Eeil is a very small lobule of brain in the fissure 

 of Sylvius, found in man but not in the horse. 



Describe the optic thalami. 



The optic thalami are two masses of gray matter, placed above 

 the crura cerebri; they are separated by a deep groove, and form 

 the sides of the third ventricle. At their posterior border are found 

 two projections, the external and internal geniculate bodies. 



Describe the cerebellum. 



The cerebellum is that part of the brain, situated behind and 

 beneath the cerebrum, above the isthmus and separated from the 

 cerebrum by a fold of the dura mater. 



It is globular in form and is divided by two fissures into three 

 lobes, two lateral and a middle. The lateral lobes are convex and 

 show many convolutions or depressions. The middle lobe is dis- 

 posed in a vermicular manner, which gives rise to the names of the 

 two divisions, anterior vermiform and superior vermiform 

 processes. 



The structure is gray externally and white internally with a 

 tree-like arrangement called the arbor viice. 



Describe the corpora quadrigemina. 



These are four round eminences, placed in pairs, which lie 

 above the cerebral peduncles. The two posterior, the smallest, are 

 also named the tuhercula testes, and the anterior pair, the tubercula 

 nates. The nates are gray and the testes are white. 



Describe the spinal cord, using a diagram. 



The spinal cord is the portion of the nervous system which is 

 enclosed in the spinal canal from the occipital foramen to the upper 

 third of the sacral canal. Its average weight in the horse is 10% 

 ounces. It is slightly flattened above and below, and has two enlarge- 

 ments in its course, one between the fifth cervical and second dorsal 

 vertebrae, the brachial bulb, the other, near the middle of the loins, 

 the lumbar enlargement. 



The structure of the cord is, externally, white matter, internally, 

 gray. The gray matter is arranged like two horns, the larger ends 

 of which point down and out, but do not reach the surface, the 

 smaller look upward and outward, reaching the surface. The two 

 horns are connected by a transverse band (similar to the letter 



