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enlargement it entirely disappears, but the whole inner half of the 

 cervix cornus is still interspersed with numerous cells of various 

 shapes, and traversed by the posterior roots and the fibres of the trans- 

 verse commissure. At the origin of the third pair of cervical nerves, 

 a darker mass reappears in the same situation, but gradually dimi- 

 nishes as it ascends to the medulla oblongata. 



The tractus intermedio-lateralis is larger in the upper part than 

 in the middle of the dorsal region, and projects further into the 

 lateral column. As it ascends, however, through the cervical en- 

 largement, it gradually diminishes, and at length disappears ; but 

 the lateral portion of the grey substance contains numerous branched 

 and elongated cells, amongst which are a few that resemble those of 

 the tractus intermedio-lateralis ; it is traversed by the anterior and 

 posterior roots, and by the lowest roots of the spinal-accessory nerve 

 on their way to the anterior cornu. In the region of the first pair 

 of cervical nerves, a distinct vesicular tract reappears at the lateral 

 part of the grey substance. It is traversed by the roots of the spinal- 

 accessory nerves, and partly by those of the spinal nerves. Its cells 

 are elongated transversely and longitudinally. Ascending the 

 medulla oblongata, this vesicular tract makes its way inwards to the 

 space behind the central canal, where it forms the nucleus of the 

 upper roots of the spinal-accessory nerve. 



In descending the cord from the dorsal region, the grey substance 

 undergoes a series of changes nearly similar to those which are 

 observed in ascending to the cervical enlargement. But in the 

 upper part of the lumbar enlargement, the posterior vesicular columns 

 are much larger than in any other region of the cord, and contain 

 more large cells. Through the rest of the lumbar enlargement the 

 number of large cells diminishes ; but they are still traversed and 

 surrounded by the posterior roots of the nerves, and by the transverse 

 commissure. 



In the spinal cord of Man, the form of the grey substance differs 

 in some respects from that in Mammalia. Throughout the whole of 

 the dorsal region the posterior cornua stand completely apart. The 

 posterior vesicular columns are oval, but in structure resemble those 

 in the Ox. In the middle of the cervical and lumbar enlargements, 

 their cells, in connexion with the posterior roots, are very small, but 

 numerous. 



