338 



behind and on each side by the gelatinous substance, with which it 

 varies in shape at different regions of the cord. In addition to 

 blood-vessels and connective tissue, it consists of, 



A. Nerve-fibres, transverse, longitudinal, and oblique. 



B. Nerve-cells, both large and small. 



A. The longitudinal fibres form bundles of various sizes, and are 

 broader and coarser than those of the gelatinous substance, which, 

 however, they immediately adjoin. 



The transverse and oblique fibres are continuous with the posterior 

 roots of the nerves, and partly with the longitudinal fibres, which 

 they also cross in a great variety of ways. 



About the middle of the dorsal region, in the spinal cord of the 

 higher vertebrata, the posterior cornua are united in a single mass. 

 The inner or median half of each cervix cornus is occupied by a 

 remarkable longitudinal column, which is cylindrical or oval, the 

 posterior vesicular column. This consists of a cylinder of fibres inter- 

 spersed with arid surrounded by cells and thin processes. The fibres 

 are derived from the posterior roots of the nerves, and interlace with 

 each other in an intricate manner. The cells are oval, fusiform, and 

 variously stellate, and differ considerably in size, but the largest 

 are equal to those of the anterior cornu. They are elongated with 

 thin processes transversely, longitudinally, and obliquely, and are 

 continuous with fibres in the same direction, including the posterior 

 roots. 



At the lateral border of the grey substance, between the anterior 

 and posterior cornua, is a small and somewhat triangular tract, which 

 is more transparent than the rest, and projects more or less into the 

 lateral column. This tract, which was pointed out by the author 

 in 1851, and is named the tractus intermedio-lateralis, consists of 

 oval, fusiform, and triangular cells, which are smaller and of more 

 uniform size than those of the surrounding substance. Some of 

 them are elongated transversely and longitudinally, transversely 

 both in a lateral and antero-posterior direction, and send their pro- 

 cesses on the one hand to the transverse commissure, and on the 

 other to the anterior and posterior cornua. 



In receding from the dorsal to the cervical region, the central 

 portion or cylinder of each posterior vesicular column is reduced in 

 size and less completely circumscribed. In the middle of the cervical 



