THE TEGMENTUM OF THE CHITS CEREBRI AND ITS GANGLIA. 449 



ficial layers of both the nates and testes. Nevertheless, in the 

 deeper layers, and more towards the centre of the section, we 

 find (perhaps most abundant in the nates) very large forms, 

 having a length of from 45 to 90 /i, and a breadth of from 10 

 to 30 JJL. These nerve corpuscles lie with their long axes in 

 three directions, so that (1) some are arranged concentrically 

 with the surface, as is particularly obvious in the superficial 

 expansion of the medulla of the arms, ex. gr., along the con- 

 vexity of the testes ; (2) others in considerable number are 

 arranged longitudinally from before backwards, especially 

 along the internal surfaces of the nates, corresponding to the 

 above-mentioned indirect course of the brachia of the nates 

 towards the median decussation (fig. 241, Q'). 3. There' are 

 also a number arranged in a radial manner around the 

 aquseduct. 



A definite arrangement of radiating cells appears to be es- 

 pecially important for the right understanding of the structure 

 of the corpora quadrigemina.. We see, particularly with high- 

 powers, in transverse sections of the deep medullary layers 

 dividing the grey matter of the ganglia and the grey matter 

 of the central cavities (fig. 241. m), that these are traversed 1 

 radially by fine fibrils. Amongst these fibrils fusiform cells- 

 are interspersed, having a length of 45 JJL, and a breadth of TO p, 

 and the two together constitute a nervous structure connecting 

 the grey matter of the corpora quadrigemina with the grey 

 matter of the aquaeductus Sylvii, in which the centres of origin 

 of the nerves for the eye are imbedded. By means of this 

 connection the above-named grey masses appear as a combined 

 and coherent centre, and the morphology thus corresponds to 

 a physiological postulate, demanded as a result of the control 

 exerted by the retina over the ocular muscles. Perhaps just 

 as the fibrse rectse of the nucleus of the third nerve are the 

 shortest fasciculi of the crusta, we may represent these radiat- 

 ing fibres for the same nucleus as their analogues among the 

 spinal fasciculi of the tegmentum, which may likewise bring 

 the motor-nerve nuclei into connection with the ganglia of 

 origin of the tegmentum. 



The mode of origin of the cms cerebri from the nates 

 and testes is the same for both pairs of ganglia. From 



VOL. II. G G 



