In the cervical region (Fig. 134) there appears between the posterior lateral and posterior median sulci an =intermediate= sulcus which divides the posterior funiculus in this region into two. The median slenderer of these is the =fasciculus gracilis= (_d_) or column of Goll. The lateral and thicker is the =fasciculus cuneatus= (_e_) or column of Burdach. _The membranes of the spinal cord_: 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. [Illustration: 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.] [Illustration: 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.] [Illustration: FIG. 136.--CAUDAL PORTION OF THE SPINAL CORD. _A_, lumbar enlargement; _B_, cauda equina; _C_, filum terminale; 5-7, fifth to seventh lumbar nerves. _I_-_III_, the three sacral nerves. _a_, dorsal roots; _b_, spinal ganglia; _c_, dorsal rami; _d_, ventral rami.] The =pia mater= invests the cord closely and contains some blood-vessels. It is a delicate membrane which dips into the fissures and sulci of the cord and is connected to it by numerous strands of connective tissue that pass from it into the substance of the cord. The nerves pierce it.