230 TWENTY-SECOND LECTURE. 



longations is an axis-cylinder process. Then two other cell 

 layers follow. This is all that we know at present. 



Here, also, Gerlach assumes the presence of a very fine 

 problematical nerve reticulum, such as we have already 

 mentioned at page 222, in connection with the gray substance 

 of the spinal cord. 



At the apex of the occipital portion, in the vicinity of the 

 so-called sulcus hippocampi, the cortical stratum becomes 

 still more complicated. The cornu ammonis also has its 

 peculiarities. 



A remarkable, although in man considerably stunted por- 

 tion, of the cerebral substance is the bulbus olfactorius. The 

 cavity, which is lined with ciliated epithelium, presents pa- 

 rietes consisting of internal white, and external gray substance. 



The former contains the root bundles, which are two in 

 number, a thicker external one, coming in part from the 

 anterior inferior cerebral convolution, in part from the corpus 

 callosum, and a thinner internal one, which is thought to be 

 derived from the corpus striatum, the chiasma nervorum opti- 

 corum and the pedunculus cerebri. 



In a strongly developed neuroglia, we meet, in an inward 

 direction, with the longitudinally arranged medullated root 

 fibers, and then, connected with these, a nerve plexus of very 

 fine tubes. We finally meet with granules and multipolar 

 ganglion cells. 



Below, or rather externally, the gray substance becomes 

 strongly altered. One here meets with globular balls of a 

 granular substance with nuclei (glomeruli nervi olfactorii, ac- 

 cording to Meynert). 



From these lumps are developed the pale nucleated fibres 

 of the special olfactory nerves. 



The apophysis cerebri has already been discussed, so far as 

 its anterior portion is concerned, in connection with the blood- 

 vascular glands (page 126) ; the posterior consists of gray 

 cerebral substance. 



The so-called Pineal gland, conarium, has long been remark- 

 able on account of its calcareous concretions. In its connec- 



