238 STUDENTS HISTOLOGY 



blood-vessels. 00 The pia. (e) Its continuity with the con- 

 nective tissue of the cerebrum. 



1. The outer layer the first of the gray substance. (This 

 layer is poorly defined, but can usually be made out. It consists 

 of primitive nerve -fibrillae, neuroglia -fibrils, and scattered gan- 

 glion-cells. A few medullated nerve -fibers run horizontally 

 tangential fibers.) 



2. The second layer. (This layer presents about the same 

 thickness as the preceding, and will be recognized by the abun- 

 dance of small triangular nerve -cells. From Golgi preparations 

 it appears that numerous protoplasmic processes pass peripherally, 

 while the axis -cylinders arise from the bases of the small 

 pyramidal ganglion-cells.) 



3. The third layer. (This layer the thickest of all the gray 

 laminae is called the formation of the cornu Ammonis [Mey- 

 nert] . The large pyramidal cells have numerous protoplasmic 

 processes arising from their sides and prominent ones from the 

 apices, while the axis -cylinders are given off from the blunt bases 

 to enter the white matter [Fig. 155] . Medullated fibers, in more 

 or less distinct bundles, pass between the column -like ganglion- 

 cells.) 



4. The fourth layer. (The large cells of the third layer are 

 seen to stop, as we pass inward, and give place to small, irregu- 

 lar nerve -cells, called the granular formation. Between the cells 

 of this layer bundles of nerve -fibers are seen, as they radiate 

 toward the cerebral surface.) 



5. The fifth layer. The line of demarcation between this and 

 the fourth layer is feebly shown; but, on close attention, it will be 

 observed that the small cells of the fourth layer rather abruptly 

 give place to spindle-shaped ones, sometimes parallel with the sur- 

 face. The nerve-bundles are here more plainly indicated. 



6. The white matter. (The ganglion -cells cease here, and the 

 field is occupied with medullated fibers and neuroglia, the spherical 

 nuclei of the latter becoming prominent from the deep haematoxy- 

 lin staining.) 



7. The nutrient blood-vessels. (The capillaries projected 

 from the pia are especialty to be noticed, often of the diameter of a 

 single blood -corpuscle, and appearing as branching lines, composed 

 of these elements indeed difficult of demonstration when empty. 

 Note the light, perivascular lymph -spaces, well seen around the 

 larger arteries in transverse section.) 



