THE SPINAL CORD. 



495 



matter. The posterior horn is narrow and elongated and extends quite 

 up to the surface of the cord, where it is capped by gelatinous matter, the 

 substantia gelatinosa. In the lower cervical and thoracic regions a portion 

 of the intermediate gray substance projects outward and forms the so-called 

 lateral horn. The gray matter fundamentally consists of a framework of 

 fine neuroglia supporting blood-vessels, lymphatics, medullated and non- 

 medullated nerves, and groups of nerve-cells. 



Superior or Cervical Segment Middle or Dorsal Portion Inferior Portion of Cord 



of Spinal Cord. of Cord. and Cauda Equina. 



FIG. 229. SUPERIOR, MIDDLE, AND INFERIOR PORTIONS OF SPINAL CORD. i. Floor of 

 fourth ventricle. 2. Superior cerebellar peduncle. 3. Middle cerebellar peduncle. 4. Infe- 

 rior cerebellar peduncle. 5. Enlargement at upper extremity of postero-median column. 6. 

 Glosso-pharyngeal nerve. 7. Vagus. 8. Spinal accessory. 9, 9, 9, 9. Ligamentum denticula- 

 tum. 10, 10, 10, 10. Posterior roots of spinal nerves, n, u, u, n. Postero-lateral fissure. 

 12, 12, 12, 12. Ganglia of posterior roots. 13, 13. Anterior roots. 14. Division of united roots 

 into anterior and posterior nerves. 15. Terminal extremity of cord. 16, 16. Filum terminale. 

 17,17. Cauda equina. I, VIII. Cervical nerves. I, XII. Dorsal nerves. I, V. Lumbar nerves. 

 I, V. Sacral nerves. (Sappey.) 



The Nerve-cells. The nerve cells of the cord are very numerous and 

 they present a variety of shapes and sizes in different regions. They are 

 usually arranged in groups which extend for some distance up and down 

 the gray matter, forming columns more or less continuous. 



In the anterior horn two well-marked groups are found, one situated at 

 the anterior and inner angle, known at the antero-median group, the other 

 situated at the posterior and lateral angle and known as the postero-lateral 

 group. In the lower cervical and upper thoracic regions, in the region of 



