785 



taining a great quantity of pigment are to be seen. It is not improbable 

 tliat these are central ganglion cells of spinal ganglions. 



Bos t/iufus. (foetus of A^/^ months). (_)n tlie border of the lumbal 

 and sacral portion the medulla shows a sectional view which 

 resembles exactly that of the closed portion of the medulla oblon- 

 gata of the cow, in the reverse way, however, for the cleft is 

 caused by the fissura anterior and thus lies here on the frontal side. 

 The walls of this fissure diverge widely and gradually slope into 

 the frontal wall. The strongly developed anterior horns are extremely 

 rich in cells in the ventral portion ; latero-dorsally on the border 

 of anterior and posterior horns no cells of a large type are met 

 with. As a rule three sharply defined cell-groups may be distinguished 

 in the anterior horn, one ventro-medial, one ventro-lateral and one 

 dorsally at the last-named. This dorso-lateral group is the most 

 constantly round in form and contains 30 — 40 cells, the two 'other 

 differ greatly in size and shape, owing lo their often possessing 

 continuations which continue along the lateral and medial walls respec- 

 tively. The dorsal horns are broad and carry a heavy cap of 

 substantia gelatinosa Rolando, always clearly circumscribed on the 

 periphery by a fibre system. These horns are also rich in cells, of 

 a smaller type, however, than those of the anterior horns. The canalis 

 centralis is a recumbent oval in section, in width it measures 0.1 mm. 

 and in depth 0.07 mm.; the ciliated epithelium is very well developed. 

 The fissura anterior is shallow, regular in section and proceeds, as has 

 been remarked, with a pronounced curve into the frontal wall of 

 the medulla. In this foetal tissue the commissura grisea is very 

 slightly developed, when, strongly magnified, but few commissure 

 fibres can be detected, a circumstance which can be observed also 

 in the whole of the lumbal segment (fig. 9). 



Caudally the cross diameter of the conus decreases, whereby the 

 form on section becomes compact, the central canal shifts in a 

 ventral direction and on section is seen to be round; the cell groups 



Fig. 9. Fig. 10. 



Bos taurus (Embryo 4V3 months). 



