The dura mater is a tough fibrous membrane directly continuous with the dura mater of the brain. It differs from the dura mater of the brain in two particulars:
1. At the foramen magnum it splits into two layers, one of which lines the bony vertebral canal and forms its periosteum, while the other covers the cord.
2. It is separated from the cord by a considerable space. The dura mater is continuous with the fibrous sheaths of the spinal nerves at their points of exit. Along the sides of the cord it is connected to the pia mater by a delicate strand of connective tissue probably equivalent to the “ligamentum denticulatum” of man.
The arachnoid is a delicate cellular membrane lying beneath the dura mater, between it and the pia mater. It forms a continuous investment for the cord, is not vascular, and is said not to dip into the fissures of the cord.
Fig. 134.—Cross-section of the Spinal Cord in the Cervical Region.
a, posterior median sulcus; b, posterior lateral sulcus; c, anterior median fissure; d, fasciculus gracilis; e, fasciculus cuneatus; f, white matter; g, gray matter; h, central canal.
Fig. 135.—Section of Spinal Cord, showing the Origin of a Pair of Spinal Nerves.
a, dorsal root; b, spinal ganglion; c, dorsal ramus; d, ventral ramus; e, ventral root.