PART V.

DISEASES OF THE CORD PROPER.

CHAPTER I.

LOCALIZATION.

Anatomical Considerations.-The spinal cord reaches from the foramen magnum to the lower border of the body of the first lumbar vertebra. From its lower portion the lumbar and sacral nerve-roots extend to their several intervertebral foramina and make up the cauda equina, which occupies the dural sheath from the lumbar enlargement of the cord to the bottom of the sacral canal. The relations of the cord to the surface of the body and to the vertebral bodies and the spinous processes are shown in figures 114 and 115.

The cord is to be considered as made up of a number of similar and partly independent segments corresponding to the vertebral bodies, and each bearing a pair of spinal nerves. In addition it furnishes a longitudinal pathway for afferent and efferent nervous impulses. In early fetal life these cord-segments are in apposition with their corresponding vertebræ, but become gradually displaced upward as the spinal column outgrows the cord. At birth the lower end of the cord is opposite the third lumbar body. The nerve-roots, as a result of the unequal vertical growth of the cord and spine, become progressively longer from top to bottom, and in the same way the spinal-cord segment occupies a position relatively higher than its vertebral centrum. In the cervical region this amounts to the height of about one vertebral body, and in the dorsal region to about one and a half vertebral bodies. The five lumbar, five sacral, and one or two coccygeal segments are crowded into the lumbar enlargement below the upper level of the eleventh dorsal and above the second lumbar vertebral body.

In estimating the position of the various vertebral bodies we are guided by the subcutaneous tips of the spinous processes. It will be recalled that these have a downward direction in the cervical and dorsal region and overlap the body of the vertebra below. Thus the tip of the eighth dorsal spine is on a level with the ninth dorsal body. Reference to figure 115 will make this clear. It follows that the exit of the spinal root at the intervertebral foramen has only a relative relation to

the cord-segment from which it originates. Cord-lesions, are, therefore, always above the level of their spinal-nerve symptoms.

Every spinal-cord segment possesses motor, sensory, and reflex functions besides vasomotor, visceral, and trophic activities. These are related to corresponding body-segments, which are shown in their cutaneous extent in figures 17 and 20. Their relation to the viscera has already been indicated (see p. 56).

Fig. 114.-The numerals indicate the relations of the vertebral bodies and spines to the corresponding spinal segments of the cord.

Cross-sections of the cord show that the gray and white matter vary in proportionate area and outline at different levels (Fig. 117). The white matter is divided into numerous zones and tracts. One division is based on the embryological development of the various tracts (Fig. 118). From dissections, physiological experiments, and especially from the results of morbid processes, we have still further division of the tracts. These are shown in

figure 119 for the ascending degenerations which follow complete division of the cord, and for the descending degenerations after similar lesions.

The H-shaped cross-section of the gray matter shows numerous cellbodies. Of these the anterior cornual groups are the best understood and contain the cell-bodies of the lower motor neuron through which motor, trophic, and vasomotor influences are exercised over the muscles, bones, and skin. The central canal is situated in the gray commissure. The essential elements of the cord are supported by fibrous tissue which is continuous with the penetrating septa of the pia mater.

The circulation in the cord is one of its most important anatomical features. Many of the cord diseases are due to vascular lesions or infections, and both their vertical distribution and lateral outlines in transverse sections may be limited to the corresponding arterial fields.

Fig. 116.-Cross-section of cervical spinal cord, showing its anatomical subdivisions (Schaefer).

The arterial supply of the cord consists of two systems, anterior and posterior. The anterior spinal artery, arising within the skull by two roots from the vertebrals, extends the entire length of the cord at the anterior fissure (Fig. 121). It is reinforced by branches from the intercostal, lumbar, and sacral arteries, which follow the corresponding nerves into the spinal canal and accompany the nerve-roots to the cord. The anterior spinal artery gives off about three hundred branches, called anterior median arteries, which penetrate the anterior fissure at a right angle to the parent stem. At the commissure they enter the cord and without dividing turn toward the right or left anterior horn. At the neck of the horn the artery divides into an anterior branch to the anterior horn and a posterior branch which is distributed to the neck and to a portion of the posterior horn. A branch is also given off in a

Fig. 117.-Transverse sections of the cord at various levels, to show the relative variations in gray and

white matter.

Fig. 118.-Divisions of the cross-section of the cord based on Flechsig's study of their development. A, Direct pyramidal tract; B, fundamental fasciculus of the anterior column; C, rest of lateral column. D. direct cerebellar tract; E, crossed pyramidal tract; F, lateral limiting zone; G, anterior root zone; H, middle root zone; I, median zone; J, column of Goll; K, postero-internal root zone; L, posteroexternal root zone or zone of Lissauer (Marie).

Fig. 119.-Scheme showing secondary degenerations. Ascending degenerations: 1, Fibers of the ascending sulcomarginal fasciculus; 5, Gowers, tract; 7, direct cerebellar tract; 8, cornucommissural tract; 9, column of Burdach; 10, the external root zone tract; 11, zone of Lissauer; 12, column of Goll. Descending degenerations: 2, Descending sulcomarginal tract; 3, direct pyramidal tract; 6, crossed pyramidal tract; 13, comma-shaped tract of Schultze (Marie).