THE STRUCTURE OF THE SPINAL CORD. 



727 



Level of 



I he first 



cervical nerv< 



III. Cervical nerve. 



VI. Cervical nerve. 



Then there develop fibers that connect the different centers in the gray matter 



of the cord. Next there appear fibers that connect the gray matter of the cord 



with the cerebellum, and also the 



former with the tegmentum of 



the cerebral peduncle. Finally, 



there develop the fiber-systems 



that connect the ganglia of the 



pes of the cerebral peduncle and 



perhaps also the gray matter of 



the cerebral cortex with the gray 



matter of the spinal cord. The s'^^mar /'W--\ ^Xi^ ^ 7, 



pyramidal tracts at the time of 2 /^ / Hi S^T^* '' s ^ 



birth are still non-medullated. In g ^/~J^p j ^^ 



cases of congenital absence of the 



cerebrum, neither the pyramids 



nor the pyramidal tracts develop. 



Even prior to birth myelinated 



fibers develop in the brain in the 



paracentral lobule, the central 



gyri, the occipital lobe, the island 



of Reil, and latest in the frontal 



lobes. 



The connective tissue of the 

 spinal cord is derived in part from 

 the pia mater and penetrates with 

 the vessels only into the white 

 matter, to separate the nerve- 

 fibers into separate bundles. From 

 it the neuroglia must be distin- 

 guished -. the true supporting 

 tissue. This is not a connective 

 tissue, being derived from the 

 ectoderm. It consists of a homo- 

 geneous, structureless, semisolid 

 ground-substance, together with 

 spider-shaped, star-shaped, or 

 tree-shaped glia-cells, intricately 

 interwoven, and nucleated or non- 

 nucleated fibers composed of 

 keratin. The function of the 

 neuroglia is to afford a support- 

 ing framework for the nerve- 

 tissues, to protect them from 

 pressure and to isolate them. In 

 addition it forms channels for the 

 fluids, or lymphatic passages, 

 without endothelial lining, for 

 the lymph so abundantly given 

 off by the nervous elements, 

 especially the ganglia, as a result 

 of their activity, to eventually 

 reach the perivascular spaces or 

 the subpial space directly. This 

 supporting tissue is much denser 

 around the central spinal canal 

 than the so-called central epen- 

 dyma- fibers; further, it is more 

 abundant at the apex and the 

 margins of the posterior horns, 

 where it is known as the gelatin- 

 ous substance of Rolando. The 



npurno-lia ic -nrpc^nt liV^Turicp. in FlG - 253. Diagrammatic Representation of the Principal Tracts 

 neuroglia IS present likewise in O f the Spinal Cord: 1^5, Anterior pyramidal tracts (direct); 



the cerebrum. I he ganglion- ( 2 ) a psb, lateral pyramidal tracts (crossed); (3) 3 ksb, direct 



Cells are surrounded bv CUp- cerebellar tracts; (4)4dks, external column of Burdach; (5) 



cl-ia-n<=>rl KrmT->Vi c-na/-e>c ^ 5 < internal column of Goll; (6) 6vsr, combined anterior 



ground-bundles. Gowers' column, and lateral ground-bundles. 



Ill. Dorsal nerve. 



VI. Dorsal ner 



XII. Dorsal nerve. 



IV. Lumbar nerve. - 



