HEMISPHERES. 349 



branched neuraxons limited to the vicinity of the cell body are found in 

 this layer and in the pyramidal layers also. The neuraxon may branch 

 in the molecular layer (Fig. 402, 6). 



Many medullated fibers are found in the deeper pyramidal and 

 polymorphous layers. They are grouped in tapering radial bundles 

 which are resolved into separate fibers toward the layer of small pyramidal 

 cells (Fig. 403). The bundles include the descending medullated neu- 

 raxons of the pyramidal cells, and the ascending medullated fibers from the 

 white substance, which end after branching repeatedly in the supra-radial 

 and tangential networks. The medullated collaterals of the pyramidal 

 cells run at right angles with the radial bundles; they form an inter-radial 

 network, or a band of fibers which near the calcarine fissure is macroscopic. 

 A similar supra-radial band may be detected elsewhere in thick sections. 



In the gyrus hippocampi and its hook (uncus) the tangential fibers 

 are so abundant as to form a considerable layer, the substantia reticularis 

 alba. The hippocampus [Ammon's horn], olfactory bulb, and some other 

 areas of the cortex, differ in details from the central region which has been 

 described; these peculiarities are considered in the larger special works on 

 the nervous system. 



The neuroglia of the hemispheres, like that of the cord, is at first a 

 syncytium with strands extending from the ventricle to the periphery. 

 Later, the syncytium is divisible into short-rayed neuroglia cells found 

 chiefly in the gray substance, long-rayed cells found chiefly in the white, 

 and ependymal cells lining the ventricles. The ependymal layer is con- 

 tinuous through the aqueduct with that of the fourth ventricle and central 

 canal. In early stages its cells have cilia-like processes which are in part 

 retained in the adult. The short-rayed cells, which are characterized by 

 knotted, branching processes, are often in close relation with the blood 

 vessels; they may serve to transfer the nutritive and myelin-forming 

 material from the vessels to the nerve fibers. The periphery of the 

 cerebral cortex is particularly rich in neuroglia fibers. 



HYPOPHYSIS. 



The development of the two lobes of the hypophysis [pituitary 

 body], the anterior from the oral ectoderm and the posterior from the 

 telencephalon, has already been described (Fig. 185, p. 165). The 

 smaller posterior lobe, which is at the tip of the infundibulum, contains fine 

 branching nerve fibers which form a delicate network, together with 

 cells closely resembling bipolar and multipolar ganglion cells, and many 

 blood vessels. The nature of the cells is, however, uncertain. The 

 larger anterior lobe consists of loose connective tissue with many blood 



