OP THE ETJMINAl^TIA. 



55 



of the opposite side, and, in so doing, crosses and interdigitates 

 with the inner layer of- the other side as it runs outwards also. 



Fig. 2. 

 Line of decussation. 



Outer layer. 



Outer layer. 

 B 



B Inner layers. -^ 



Inner layer (A) becomes the outer layer (A). 

 Inner layer (B) becomes the outer layer (B). 



On examining one of the lines of decussation more minutely on 

 both its outer and inner aspects (Plate III. figs. 1 & 3), it will be 

 observed that, whereas internally the crossing is clear and distinct, 

 externally it is obscure. This is caused by bundles of fibres of the 

 outer layer, which, instead of dipping down to become internal, 

 continue over the decussation to the outer layer of the other side 

 (Plate III. fig. 1, a). These fibres, for the sake of convenience, 



Fig. 3. 

 Non-decussating bundle. 



Fig. 4. 



Outer layer. ^ ^ ""^^ '*** Outer layer 



Inner layers. 



may be termed the non-decussating bundles — an incorrect term, 



however ; for, if these bundles be traced round to the other line of 



decussation, they will always be found to decussate 



there, and pass into the inner layers. Purther, 



the concavity of the non-decussating bundles (for 



they all run obliquely) (fig. 7) looks at the one 



decussation upwards, at the other downwards. At 



both decussations, all the fibres of the inner layers 



run into the outer layers ; but all the fibres of the 



outer layers do not, in like manner, run into the 



inner layers, but the half of the fibres of the outer 



layer of one side runs over the decussation into the 



outer layer of the other side ; and whether you trace 



these non-decussating bundles upwards from the one 



decussation, or downwards from the other, they will 



always be found to decussate at the decussation of 



the opposite side, so that they do not form a layer 



of circular fibres. 



A bundle of 

 fibres not de- 

 cussating at 

 one decussa- 

 tion,running 

 round to the 

 other (decus- 

 sation), and 

 tliere decus- 

 sating. 



5* 



