'286 PRACTICAL ANATOMY. 



downward and forward, dividing into two branches, one 

 of which communicates with the calcarine fissure. The 

 calcarine fissure is a short, deep, horizontally placed fis- 

 sure below the posterior bulbous part of the corpus callo- 

 sum. It causes an elevation on the floor of the posterior 

 cornu of the lateral ventricle, called the calcar, or hippo- 

 campus minor. Above the uncinate gyrus is a short, 

 deep fissure, which extends deeply into the descending 

 cornu of the lateral ventricle, forming on its floor and 

 inner aspect the fascia dentata. Below the uncinate 

 convolution is a long fissure, called the collateral. It 

 causes an elevation on the floor of the posterior cornu 

 of the lateral ventricle, designated the emmenentia col- 

 lateralis. The base of the brain is flattened and irregular, 

 and presents for examination the frontal and temporo- 

 sphenoidal lobes, the pons Varolii, medulla oblongata, 

 cerebellum, and a number of structures along the median 

 line. From before backward, the following points are 

 seen : 



1. Longitudinal Fissure. The deep, vertical, longi- 

 tudinal fissure that divides the two hemispheres of the 

 cerebrum. It is bridged by the corpus callosum. 



2. Corpus Callosum. The white, transverse com- 

 missure between the two cerebral hemispheres. It is 

 about four inches long, and is placed about the junction 

 of the upper three-fifths and lower two-fifths of the 

 inner surface of the cerebrum. It is bodily advanced so 

 as to encroach upon the anterior portion of the cerebral 

 hemispheres. 



3. Olfactory Bulbs, Tracts, and Roots. The first 

 pair of nerves. The bulbs are the anterior enlarged 

 extremities of the olfactory tracts. They lie on the 

 cribriform plate of the ethmoid, through which they 

 send numerous filaments into the nose. The tracts lie 



