KESTEVEN ON THE ANATOMY OF THE SPINAL COED. 383 



anterior commissure. In ascending towards the lumbar region the two 

 lateral cornua, and the ijosterior commissure begin to appear. In the 

 conus medullaris the central canal is larger than in any other region 

 of the cord. It continues to enlarge through the lower part of the 

 coiius, nearly reaches the anterior fissure, and extends backwards to 

 the gelatinous substance, in front of which it dilates in a lateral direc- 

 tion. The grey substance gradually decreases in quantity, and is 

 encroached upon by the antero-lateral columns. Numerous small 

 cells are scattered throughout it. 



The Jilum terminale, in its natural state, appears to be a nearly 

 cylindrical tubule, but, when hardened in spirit, or chromic acid, is 

 more or less flattened at the sides, so that the canal becomes com- 

 pressed and sometimes completely coUapsed. The grey substance is 

 at last reduced to a mere fringe from the edges of which a series of 

 processes extend through the white substance to the pia mater at the 

 surface. 



On examining the cord upwards from the conus towards the lum- 

 bar enlargement, certain modifications are found to take place in the 

 form and disposition of the grey masses. The two halves of the 

 posterior mass begin to separate from each other at the middle line. 

 The rudiments of the posterior cornua begin to be marked out by the 

 separation of the grey matter, and the first appearance of the pos- 

 terior vesicular columns is an increasing mass of caudate cells a 

 little behind the spinal canal. The changes continue to increase from 

 below upwards, and reach their greatest extent in the middle of the 

 lumbar region, where the posterior cornua are broad and long, and 

 widely separated, while the posterior commissure is reduced in breadth, 

 ^©i'^g T3^ of ^^ ^^h instead of -^-^ as at the lower end of the cord. 



A similar series of alterations takes place also in the form and 

 arrangement of the anterior grey horns, whereby they assume a shape 

 the opposite of what they presented lower down. They now turn 

 rather outwards than inwards, and have a large irregularly clubshaped 

 extremity. The caudate vesicles have become exceedingly numerous, 

 and are grouped together in several large masses, chiefly on the outer 

 and middle parts of the cornua. 



In the dorsal region the arrangements of the grey substance are 

 again reversed. The posterior grey substance again consists of a 

 single mass extending uninterruptedly and nearly horizontally across 

 from side to side — on the other hand, the anterior cornua are long, 

 straight and narrow, projecting directly forward. Its caudate vesicles 

 are less numerous and collected in one or two small groups towards 

 their extremities. 



From the middle of the dorsal region to the cervical enlargement 

 of the cord, the alterations in the form of the grey substance are 

 again reversed, being nearly similar to those found to take place on 

 proceediug upwards from its lower extremity. The process of division 

 of the posterior mass is renewed, the commissural bands are pressed 

 forward, marking the posterior cornua — the anterior become broader 



