Quain's elements of anatomy . Hence it is sometimes named the motor ganglmiic cohimn, but it is moregenerally known as the ganglionic or vesicular column of the anterior cells are in some parts collected into two groups, a lateral nearerthe lateral column of white matter, and a mesial nearer the anteriorcolumn ; in the lumbar enlargement there is a third, more deeply seated,posterior group (fig. 252). Some of the cells which are nearer theanterior commissure send their axis-cylinder processes through this tothe other half of the cord : it is believed that these processes may beconnec
Quain's elements of anatomy . Hence it is sometimes named the motor ganglmiic cohimn, but it is moregenerally known as the ganglionic or vesicular column of the anterior cells are in some parts collected into two groups, a lateral nearerthe lateral column of white matter, and a mesial nearer the anteriorcolumn ; in the lumbar enlargement there is a third, more deeply seated,posterior group (fig. 252). Some of the cells which are nearer theanterior commissure send their axis-cylinder processes through this tothe other half of the cord : it is believed that these processes may beconnected with nerve-fibres of the corresponding anterior root of theother side. MICEOSCOPIC STEUCTUEE. 273. In some of the lower vertebrates it may be made out tliat there are variationsin the size of this column of cells in successive portions of the cord, the cells beingmore numerous opposite the points of entrance of the nerve-roots, the at-tachment of which to the cord is in them more localized than in man andhio-her vertebrates. In this way somewhat of a segmental formation of the colmnnis indicated, and in some fishes and reptiles the enlargement of the group of cellsand its enclosing grey matter is sufficiently marked to produce an external swell-ing opposite each nerve-pair. Fig. 253.—A S3IALL POK- Pig- 253. TWS OF A TRANSVERSESECTION OF THE SPIXAT/CORD AT THE PLACEWHERE TWO BUNDLES OPTHE FIBRES OF THE AN-TERIOR ROOTS PASS INTOTHE GREY SUBSTANCE. (AEen Thomson.) g^j-, «.. a, two bundles offibres of the anterior rootpassing through the whitesubstance of the cord, d,d; b, b, fibres runningbackwards through thegrey substance towardsthe posterior cornua; c,c, others spreading in thea
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