NETTROLOGY 295 



A fine granular ground substance. 



A fourth widely extended cell layer. 



A fine granular layer. 



A somewhat thick layer of spindle-shaped cells. 



A layer of medullated nerve fibers. 



This last is the inner layer of nerve fiber. On the inner surface 

 of this layer we find the ependjrmal cells, the cells that Une the cavity 

 of the optic lobes. The commissura Sylvii form the covering of the 

 lobi optici and join these two lobes. This commissure is formed 

 from the upper and the lower layer of nerve fibers. In the commis- 

 sure these fibers cross each other. 



The hypophysis (Fig. 62, No. C, 20) hes back of the chiasm, or 

 optic commissure, and below the middle of the third ventricle. The 

 inf imdibulum, a pedicle-Uke structure, connects the hypophysis with 

 the third ventricle of the cerebri. It contains a cavity and forms 

 an extension of the third ventricle. The hypophysis is divided into 

 two lobes, an anterior and a posterior. 



The third ventricle communicates anteriorly with the lateral 

 ventricles of the cerebri through the foramen of Monro, and pos- 

 teriorly with the fourth ventricle through the aqueduct of Sylvius. 

 The posterior walls of the third ventricle are relatively thick and 

 form the posterior brain commissure. The wall is thin from the 

 commissure to the chiasm. Within it lie two ridges, which connect 

 the two hemispheres with the corpus caUosum, and, farther ante- 

 riorly, with the anterior cerebral commissure. The space from 

 the third ventricle and to the anterior commissure is called the 

 laminae terminales. 



The pineal gland, located between the cerebri and the cerebellum, 

 hes against the choroid plexus, which covers the highest point of 

 the third ventricle. 



The cerebrum is divided by a deep longitudinal fissure into two 

 hemispheres. The cerebrum is shaped somewhat like the heart on 

 a plapng card. The lower face is somewhat flattened. The upper 

 and lateral sides are not pro-vided with convolutions or sulci, but 

 are smooth. The fissure of Sylvius is faintly marked on the inferior 

 face. The olfactory lobes appear well developed and are relatively 

 large for the size of the brain. They he close together on the extrem e 

 anterior portion in the median line. 



The olfactory cerebral crura emerge from the cranium at th e 

 upper angle between the posterior wall, the roof, and the septum o f 



