786 



in the anterior horn have grown fewer in number and smaller, the 

 commissiira grisea begins to be clearly visible on tiie peri[)heral 

 portion and further develops rapidly and grows very rich in small 

 cells. The border zone of the posterior horns lies directly against 

 the periphery. Further caudally, in the niedio-ventral portion of the 

 anterior horn, many cells again appear, and conspicuous is a well-defined 

 cell-group right and left of the canalis centralis. These groups built up 

 of typical anterior horn cells, can be traced for many sections (fig. 10). 

 The conns then becomes roundish in form, only broken in its 

 frojital wall by tiie shallow fissura anterior, the central canal has 

 become egg-shaped on section with the blunt end pointing ventrally ; 

 the septum posterius has disappeared; the commissura grisea is very 

 broad and rich in small cells, in the anterior horn a varyingly large 

 number of cells occur of a smaller type than before; after this the 

 conns flattens and its section shows the form of a kidney, the 

 central canal keeps its diameter and remains free; the number 

 of cells has diminished very greatly everywhere; in the anterior horn 

 we see exclusively small cells of 10 — 12 ft, sometimes in groups 

 3 — 5. By the time the fissuia anterior has disappeared, the frontal 

 wall of the conus is flattened, the posterior wall remains rounded, 

 the central canal is then rather wider, (0.13 >, 0.1 mm.) and is also 

 flattened on the frontal side. Now the canal begins gradually to widen 

 into the ventriculus terminalis. First egg-shaped on section witli the 

 pointed end towards the front, it further on expands backwards 

 whereby the posterior wall of the canal becomes flat. At the base 

 traces of folds can now and then be seen (fig. 11). The breadth 

 diameter of the conns diminishes greatly so that, when the canal has 

 reached its maximum breadth and its front and back walls have 

 very nearly reached the periphery, the whole canal is surrounded 

 by a narrow strip of couus-tissue (fig. 12). The ventriculus is then 



Fig. 11. Fig. 12. 



Bos taurus Embryo 4Vij month. 



1.1(3 mm. deep and 0.250 mm. broad; the epithelium here shows 

 signs of degeneration, and cell remnants are present in the ventriculus. 

 Then the latter decreases in width and gradually becomes a narrow 

 groove; before the end, however, a slight widening takes place, 



