MINUTE STRUCTURE OF THE CORD. 



509 



iu fishes, reptiles, and birds than in mammals. In the young human subject 

 it is always present, but, according to the observation of Lock hart Clarke 

 and Kolliker, it sometimes disappears in the adult. 



Minute Structure of the Spinal Cord. The substance of the spinal cord consists of a 

 large proportion of nervous substance, supported in a delicate framework of connective 

 tissue and numerous minute blood-vessels. The white matter presents nerve-fibres, 

 but is destitute of nerve-cells the grey matter contains both elements. The fibres 

 of the white substance are in greatest part longitudinal; the principal exceptions 

 being those contained in the commissure, and in the roots of the nerves. The longi- 

 tudinal fibres are finer in the posterior columns and posterior parts of the lateral 

 columns than in other parts, and the deepest fibres are smaller than those placed more 

 superficially. (Kolliker.) The fibres of the grey substance are for the most part not 

 more than one half the diameter of their continuations in the white substance, and in 

 the nerve-roots, but among them there are a few of larger size. They are very 

 various in their direction, and, in great part at least, are connected with the roots of 

 the nerves. 



Fig. 345. TRANSVERSE Fig. 345. 



SECTION OP HALF THE 

 SPINAL MARROW IN 

 THE LUMBAR EN- 

 LARGEMENT, f 



This is a semidia- 

 grammatic representa- 

 tion taken from a pre- 

 pared specimen, and 

 founded in part on the 

 statements of Lockhart 

 Clarke and of Kolliker. 



1, anterior median 

 fissure ; 2, posterior 

 median fissure ; 3, cen- 

 tral canal lined with 

 epithelium ; 4, posterior 

 commissure ; 5, anterior 

 commissure ; 6, posterior 

 column ; 7, lateral co- 

 lumn ; 8, anterior co- 

 lumn ; (at each of these 

 places and throughout 

 the white substance the 

 trabecular prolongations 

 of the pia mater are 

 shown ; ) 9, posterior 

 roots of the spinal nerve 

 entering in one principal 

 bundle; 10, anterior 

 roots entering in four 

 spreading bundles of 

 fibres ; a, a, caput cornu 

 posterioris with large 



and small cells, and above them the gelatinous substance ; b, in the cervix cornu, decus- 

 sating fibres from the nerve roots and posterior commissure ; c, posterior vesicular 

 columns (of Clarke) ; d, fibres running transversely from the posterior commissure into 

 the lateral columns : near d, the lateral group of cells ; e, e, fibres of the anterior 

 roots entering the anterior cornu, and passing through among the radiating cells, but 

 not joining their processes; e', fibres from the anterior roots which decussate in the 

 anterior column ; e", external fibres from the roots running round the outside of the 

 anterior grey cornu towards the lateral columns ; f, fibres from the posterior commissure 

 and from the posterior cornu running towards the anterior. Three groups of cells are seen 

 in the anterior column ; of these the anterior are external and internal, the posterior are 

 chiefly external or lateral. 



