LATERAL VENTRICLES FORNIX. 41 T 



relative proportion. They are regarded as the ganglia, or 

 centres of motion, seeing their fibres come mostly from the 

 motor tract. 



They are separated from the thalami by the tcenia semi- 

 circularis, which is a narrow medullary band, dividing 

 these two sets of ganglia from each other, and extending 

 from the corpus geniculatum externum, upon the optic thal- 

 amus, to the descending crus of the fornix. Its function is 

 considered commissural. 



The Lateral Ventricles (Fig. 11 7) are cavities occupying 

 the centre of the brain. Each of them has three cornua 

 the anterior passing forward in the anterior lobe ; the mid- 

 dle winding downward, forward, and outward into the 

 middle lobe; and the third, or posterior, passing back into 

 the posterior lobe. These ventricles are large, horizontal, 

 but very irregular cavities, bounded above by the corpus 

 callosum, having for their floor the corpora striata, thalami 

 optici, and fornix ; and separated from each other by the 

 septum lucidum. 



The anterior cornu presents nothing of any great import- 

 ance, except the corpus striatum, already noticed. In the 

 middle cornu is seen the hippocampus major, or cornu am- 

 monis, a large, winding, and beautifully white body con- 

 vex externally, and concave internally. It follows the 

 whole extent of this cavity, occupying its floor, and fermi- 

 nates in some tubercles called pes hippocampi. This body is 

 the continuation of the primary convolution, called " ourlet" 

 Its internal edge is loose and concave, presenting a narrow 

 white band, called tcenia hippocampi, or corpus fiiribriatum. 

 Beneath the taenia a narrow cineritious line is seen, named 

 from its serrated appearance, corpus denticulatum or fascia 

 dentata. In the posterior cornua a smaller eminence is ob- 

 served, the hippocampus minor, white externally and gray 

 within. 



Fornix. This body, (Fig. 116,) so called from its arch or 



vault-like appearance, is triangular in its shape and forms 



the roof of the third ventricle. It is situated beneath the 



corpus callosum and septum lucidum, next to be examined. 



27 



