medulla oblongata; D, a section through the middle of the cervical enlargement of the cord; E, through the upper dorsal region; F, through the lower dorsal region; G, through the middle of the lumbar enlargement; and H, near the lower end of the conus medullaris. 1 to 6 refer to parts of the medulla oblongata; the remaining numbers to parts of the spinal cord. 1, pyramids; 1', their decussation; 2, olivary bodies; 3, lateral columns; 4, fourth ventricle; 4', calamus scriptorius; 5, funiculus gracilis; 6, funiculus cuneatus; 7, 7, anterior median fissure of the spinal cord; 8, 8, posterolateral groove corresponding to the attachments of the posterior nerve-roots; 9, 9, posterior median fissure; x, tapering extremity of the cord; x, x, in B', filum terminale. cord is not, however, of uniform diameter throughout, but is swollen out in the cervical and lower dorsal regions, two enlargements being thereby produced-an upper or cervical (brachial), and a lower or lumbar (crural) (fig. 4). Of these the cervical enlargement is of greater size and extent than the lumbar. It extends from the upper limit of the cord to the body of the first or second thoracic vertebra; it is largest opposite the fifth or sixth cervical vertebra, where it measures from 13 to 14 mm. from side to side. The lower or lumbar enlargement begins at the tenth thoracic vertebra, is largest opposite the twelfth (11-13 mm. across), and from this point becomes gradually smaller; its antero-posterior diameter is more nearly equal to the Fig. 5.-DIAGRAMMATIC VIEW FROM BEFORE OF THE SPINAL CORD AND MEDULLA OBLONGATA, INCLUDING THE ROOTS THETIC. (Allen Thomson.). The spinal nerves are enumerated in order on the right side of the figure. Br, brachial plexus; Cr, anterior crural, 0, obturator, and Sc, great sciatic nerves, coming off from lumbo-sacral plexus; x, x, filum terminale. a, b, c, superior, middle and inferior cervical ganglia of the sympathetic, the last united with the first thoracic, d; d', the eleventh thoracic ganglion; 7, the twelfth thoracic (or first lumbar); below 8 8, the chain of sacral ganglia. transverse than is the case in the cervical enlargement. Below the lumbar enlargement the cord tapers in the form of a cone (conus medullaris), from the apex of which the small filiform prolongation is continued downwards. The cervical and lumbar enlargements have an evident relation to the large size of the nerves which supply the upper and lower limbs, and which are connected with those regions of the cord. At the commencement of its development in the embryo the spinal cord is destitute of these enlargements, which, in their first appearance and subsequent progress, correspond with the growth of the limbs. The terminal filament (filum terminale, central ligament) (fig. 6, b, b) descends in the middle line amongst the nerves composing the cauda equina, and, reaching the lower end of the sheath opposite to the second sacral vertebra, perforates the dura mater, and receiving an investment from it, passes on to be attached with this to the periosteum of the lower end of the sacral canal, or to the back of the coccyx. It is a prolongation of the pia mater, enclosing for about half its length an enlarged continuation of the central canal of the cord (see p. 9), with a little grey matter near the upper end. Below the termination of the canal, the filum is mainly com posed of connective tissue, with blood-vessels prolonged from the anterior spinal vessels, and on either side there run in it three or four small bundles of medullated nervefibres, some of which have a few ganglion-cells. These nerve-bundles are regarded by Rauber as representing rudimentary coccygeal nerve-roots. They have no connection with the coccygeal nerves proper. The filum terminale is distinguished by its silvery hue from the nerves among which it lies. Fig. 6. VIEW FROM BEHIND OF THE LOWER END OF THE SPINAL The sheath has been opened from behind and stretched towards the sides; on the left side all the roots of the nerves are entire; on the right side both roots of the first and second lumbar nerves are entire, while the rest have been divided close to the place of their passage through the sheath. The tones of the coccyx are sketched in their natural relative position to show the place of the filum terminale and the lowest nerves. a, placed on the posterior median fissure at the middle of the lumbar enlargement of the cord; b, b, the terminal filament, drawn slightly aside by a hook at its middle, and descending within the dural sheath; b', b', its prolongation beyond the sheath and upon the back of the coccygeal bones; c, the dural sheath; d, double foramina in this for the separate passage of the ventral and dorsal (anterior and posterior) roots of each of the nerves; e, ligamentum denticulatum; Dx, and DxII, the tenth and twelfth thoracic (dorsal) nerves; LI, and Lv, the first and fifth lumbar nerves; SI, and Sv, the first and fifth sacral nerves; CI, the coccygeal nerve. Fissures.-The spinal cord is incompletely divided into a right and left half by two fissures which pass in from the middle of the anterior and posterior surfaces, and penetrate through the greater part of its thickness. Of these two median fissures the anterior or ventral (fig. 7, 1) is wider and therefore more distinct than the posterior or dorsal, although it does not, in most parts, penetrate to more than one-third the thickness of the cord, while the posterior fissure may reach more than half-way from back to front. The anterior contains a fold of the pia mater and also many blood-vessels, which are thus conducted to the centre of the cord. At the bottom of this fissure is a transverse connecting portion of white substance named the anterior or white commissure. The posterior (fig. 7, 2) is not an actual fissure, for, although the lateral halves of the cord are quite separate dorsally, there is not so much a fold of the pia mater between them, as merely a septum of connective tissue and blood-vessels prolonged from that membrane which passes in nearly to the centre of the cord (posterior septum). Its position is marked, especially in the lumbar enlargement and in the cervical region, by a superficial furrow. At its end is the posterior or grey commissure. Besides these two median fissures, a lateral furrow is seen on each side of the cord, corresponding with the line of attachment of the posterior roots of the spinal nerves. It is named the postero-lateral groove (fig. 7, c, 4). Each lateral half of the cord is Fig. 7.-DIFFERENT VIEWS OF A PORTION OF THE SPINAL CORD FROM THE OF THE NERVES. Slightly enlarged. In A, the anterior or ventral surface of the specimen is shown, the anterior nerve-root of the right side having been divided; in B, a view of the right side is given; in C, the upper surface is shown; in D, the nerve-roots and ganglion are shown from below. 1, the anterior median fissure; 2, posterior median fissure; 3, antero-lateral impression, over which the bundles of the anterior nerve-root are seen to spread (this impression is too distinct in the figure): 4, postero-lateral groove into which the bundles of the posterior root are seen to sink; 5, anterior root; 5', in A, the anterior root divided and turned up wards; 6, the posterior root, the fibres of which pass into the ganglion, 6'; 7, the united or compound nerve; 7', the posterior primary branch, seen in A and D to be derived in part from the anterior and in part from the posterior root. divided superficially by the postero-lateral groove into a posterior and an anterolateral part. The attachment of the anterior roots, however, subdivides the latter into anterior and lateral portions. An antero-lateral groove has sometimes been described in the line of origin of the anterior roots of the nerves, but usually has no real existence. The fibres of these roots in fact, unlike the posterior, do not dip into the spinal cord in one narrow line, but spread over a space of some breadth. On the posterior surface of the cord, at least in the upper part, there is on each side of the middle line a slightly marked longitudinal furrow (fig. 11) situated about one millimeter from the posterior median fissure, and marking off, in the cervical region, a slender tract, the postero-mesial column. This sulcus, which is better marked in some individuals than in others, is termed the posterior intermediate furrow. An incomplete connective tissue septum (posterior intermediate septum) extends from the furrow into the white substance of the cord. The larger remaining part of the posterior column is termed the postero-lateral column. INTERNAL STRUCTURE OF THE SPINAL CORD: RELATIVE PROPORTIONS OF GREY AND WHITE MATTER. Grey matter. When the spinal cord is cut across (figs. 8, 11, 14) it is seen that the grey matter occupies the more central parts, being almost completely enclosed by the white matter. The grey matter appears in the form of two irregularly crescentic portions on either side, united across the middle line by the posterior grey commissure before mentioned, so that its section may be compared in shape to the letter H. in the middle line amongst the nerves composing the cauda equina, and, reaching the lower end of the sheath opposite to the second sacral vertebra, perforates the dura mater, and receiving an investment from it, passes on to be attached with this to the periosteum of the lower end of the sacral canal, or to the back of the coccyx. It is a prolongation of the pia mater, enclosing for about half its length an enlarged continuation of the central canal of the cord (see p. 9), with a little grey matter near the upper end. Below the termination of the canal, the filum is mainly com posed of connective tissue, with blood-vessels prolonged from the anterior spinal vessels, and on either side there run in it three or four small bundles of medullated nervefibres, some of which have a few ganglion-cells. These nerve-bundles are regarded by Rauber as representing rudimentary coccygeal nerve-roots. They have no connection with the coccygeal nerves proper. The filum terminale is distinguished by its silvery hue from the nerves among which it lies. Fig. 6. VIEW FROM BEHIND OF THE LOWER END OF THE SPINAL The sheath has been opened from behind and stretched towards the sides; on the left side all the roots of the nerves are entire; on the right side both roots of the first and second lumbar nerves are entire, while the rest have been divided close to the place of their passage through the sheath. The tones of the coccyx are sketched in their natural relative position to show the place of the filum terminale and the lowest nerves. a, placed on the posterior median fissure at the middle of the lumbar enlargement of the cord; b, b, the terminal filament, drawn slightly aside by a hook at its middle, and descending within the dural sheath; b', b', its prolongation beyond the sheath and upon the back of the coccygeal bones; c, the dural sheath; d, double foramina in this for the separate passage of the ventral and dorsal (anterior and posterior) roots of each of the nerves; e, ligamentum denticulatum; Dx, and DxI, the tenth and twelfth thoracic (dorsal) nerves; LI, and Lv, the first and fifth lumbar nerves; SI, and Sv, the first and fifth sacral nerves; CI, the coccygeal nerve. Fissures.-The spinal cord is incompletely divided into a right and left half by two fissures which pass in from the middle of the anterior and posterior surfaces, and penetrate through the greater part of its thickness. Of these two median fissures the anterior or ventral (fig. 7, 1) is wider and therefore more distinct than the posterior or dorsal, although it does not, in most parts, penetrate to more than one-third the thickness of the cord, while the posterior fissure may reach more than half-way from back to front. The anterior contains a fold of the pia mater and also many blood-vessels, which are thus conducted to the centre of the cord. At the bottom of this fissure is a transverse connecting portion of white substance named the anterior or white commissure. The posterior (fig. 7, 2) is not an actual fissure, for, although the lateral halves of the cord are quite separate dorsally, there is not so much a fold of the pia mater between them, as merely a septum of connective tissue and blood-vessels prolonged from that membrane which passes in nearly to the centre of the cord (posterior septum). Its position is marked, especially in the lumbar enlargement and in the cervical region, by a superficial furrow. At its end is the posterior or grey commissure. Besides these two median fissures, a lateral furrow is seen on each side of the cord, corresponding with the line of attachment of the posterior roots of the spinal nerves. It is named the postero-lateral groove (fig. 7, c, 4). Each lateral half of the cord is Fig. 7.-DIFFERENT VIEWS OF A PORTION 08 THE SPINAL CORD FROM THE CERVICAL REGION WITH THE ROOTS OF THE NERVES. Slightly enlarged. (Allen Thomson.) In A, the anterior or ventral surface of the specimen is shown, the anterior nerve-root of the right side having been divided; in B, a view of the right side is given; in C, the upper surface is shown; in D, the nerve-roots and ganglion are shown from below. 1, the anterior median fissure; 2, posterior median fissure; 3, antero-lateral impression, over which the bundles of the anterior nerve-root are seen to spread (this impression is too distinct in the figure): 4, postero-lateral groove into which the bundles of the posterior root are seen to sink; 5, anterior root; 5', in A, the anterior root divided and turned up wards; 6, the posterior root, the fibres of which pass into the ganglion, 6'; 7, the united or compound nerve; 7', the posterior primary branch, seen in A and D to be derived in part froin the anterior and in part from the posterior root. divided superficially by the postero-lateral groove into a posterior and an anterolateral part. The attachment of the anterior roots, however, subdivides the latter into anterior and lateral portions. An antero-lateral groove has sometimes been described in the line of origin of the anterior roots of the nerves, but usually has no real existence. The fibres of these roots in fact, unlike the posterior, do not dip into the spinal cord in one narrow line, but spread over a space of some breadth. On the posterior surface of the cord, at least in the upper part, there is on each side of the middle line a slightly marked longitudinal furrow (fig. 11) situated about one millimeter from the posterior median fissure, and marking off, in the cervical region, a slender tract, the postero-mesial column. This sulcus, which is better marked in some individuals than in others, is termed the posterior intermediate furrow. An incomplete connective tissue septum (posterior intermediate septum) extends from the furrow into the white substance of the cord. The larger remaining part of the posterior column is termed the postero-lateral column. INTERNAL STRUCTURE OF THE SPINAL CORD: RELATIVE PROPORTIONS OF GREY AND WHITE MATTER. Grey matter. When the spinal cord is cut across (figs. 8, 11, 14) it is seen that the grey matter occupies the more central parts, being almost completely enclosed by the white matter. The grey matter appears in the form of two irregularly crescentic portions on either side, united across the middle line by the posterior grey commissure before mentioned, so that its section may be compared in shape to the letter H. |