304 



MANUAL OP HISTOLOGY. 



commissure is narrow, and the central canal has its long diam- 

 eter placed transversely to the cord. 



Transverse sections in the dorsal region are circular and 

 8 mm. in diameter. The white commissure is thin, otherwise 

 the same structure as in the lumbar region is observed. The 

 anterior horns are narrow and sparsely filled with rather small 

 multipolar cells. JN~o continuous tracts of nerve-fibres can be 

 traced through the anterior columns, as their course is so oblique 

 (downward) as to give almost a transverse section of the bun- 

 dles. The posterior horns, just behind the gray commissure, 

 are swollen out, and contain a number of large nerve-cells 

 some multipolar, some oval. They approach the type of the 

 cells in the posterior horns. This collection of cells is called the 

 column of Clarke. 



Transverse sections in the cervical enlargement measure 

 about 14 mm. The antero-posterior diameter is about 11 mm. 

 The white commissure in this region presents about the same 

 characteristics as in the lumbar region. The anterior horns are 



fan- shaped ; the anterior roots 

 curve forward, outward, and 

 downward. The central canal is 

 triangular. The posterior horns 

 are slender, and contain a few 

 small nerve-cells. The posterior 

 roots are also more intimately 

 connected with the posterior 

 horns than lower down. 



In the upper cervical region 

 the gray matter assumes more 

 the shape of the dorsal gray 

 matter. In the lateral region, at 

 the junction of the anterior and 

 posterior horns, longitudinal bun- 

 dles of myelinic nerve-fibres begin to appear. These bundles 

 curve over (see Fig. 129), and pass rather obliquely upward 

 and outward through the lateral columns, emerging nearer the 

 posterior than the anterior horns. They are joined by fibres 

 curving back from the cells of the anterior horns, and also 

 emanating from the central gray matter. In this structure is 

 seen the first appearance of the spinal portion of the spinal 

 accessory root-fibres. The longitudinal bundles mentioned 



FIG. 129. Diagram of transverse section of 

 the cord in the upper cervical region, showing 

 coarse connective-tissue reticulum in left half 

 of diagram, commencing decnssation of the 

 lateral columns across the base of the anterior 

 horn into the opposite anterior column, taking 

 the place of the anterior commissure lower 

 down, and the root of the spinal accessory, 11 : 

 A.R. = anterior root ; P.R. = posterior root. 

 In this figure and in others small crosses must 

 be understood as nerve-cells. 



