(ε) The cortical centre for sensory impressions of muscular sense, so called, is probably located in the inferior parietal lobule. The diagnosis of a lesion so placed, in a case presenting along with other sensory or with motor symptoms marked impairments of muscular sense in the arm and leg of one side, is justified by a few recent cases.12 Spitzka believes that he has clinically and pathologically demonstrated a basal path (fasciculus) for this mode of sensibility in the pons and oblongata, dorsad of the pyramidal tracts.13
12 Westphal, Charité Annalen, vii. p. 446, 1882; Stenger, Archiv f. Psychiatrie u. Nervenkrankheiten, xiii. p. 240, Case viii.; Wernicke u. Hahn, Virchow's Archiv, lxxxvii. p. 325; Ball and Seguin, Archives of Medicine, New York, v. p. 136.
13 Spitzka, “A Contribution to the Morbid Anatomy and Symptomatology of Pons Lesions,” American Journal of Neurology and Psychiatry, ii. p. 617 (1883).
(ζ) Lesions of the cortical area for common cutaneous sensibility cannot be positively recognized at the present time. By exclusion of the better-known centres, and from experimental data, we may approximately locate it in the gray matter lying ventrad of (below) the inferior parietal lobule, extending to the base, and possibly the mesal aspect, of the temporal lobe, and possibly also on the lateral aspect of the occipital lobe.
2. LESIONS OF THE KINESODIC SYSTEM OF THE ENCEPHALON.—The kinesodic system is far better understood, anatomically and physiologically, than the æsthesodic. Its limits, beginning from the junction of the cord and oblongata, are as follows: The pyramids, containing the fibres of the direct and crossed pyramidal fasciculi of the cord ([Fig. 5], Nos. 10 and 11), form the meso-basal aspect of the oblongata, appearing on either side of the median line as two large distinct bundles of white substance which enter the pons under its projecting transverse fibres. Within the pons each pyramid is divided into quite a number of fasciculi more or less separated by fibres of other systems. Again collected, these bundles constitute a considerable part of the crus cerebri—its basal middle two-fifths. (The outer or latero-dorsal one-fifth part of the crus belongs to the æsthesodic system, the middle (intermediate) two-fifths are the pyramidal fibres, and the remaining two-fifths, meso-basal part, contain some fibres from the direct cerebral motor tract destined for the hypoglossal and facial nuclei, and also large bundles probably derived from the nucleus caudatus and frontal lobes). As the crus enters the cerebrum and becomes what we know as the internal capsule, the pyramidal fibres occupy the bend or elbow of the capsule and part of its caudal segment (vide [Fig. 7]).
From this level the fibres of the internal capsule again diverge, as fasciculi whose physiological independence has been well determined, going dorsad and frontad to certain gyri of the cerebral cortex where their fibres join ganglion-cells. Three large fasciculi and corresponding cortical areas are recognized as constituting the pyramidal tract, strictly speaking: (1) A fasciculus which extends frontad to the base of the second frontal gyrus where it coalesces with the precentral, the centre and fasciculus for movements of the facial muscles of the opposite side; (2) a fasciculus which extends to the precentral and postcentral gyri, more especially in their middle part, constituting the centre and fasciculus for movements of the arm and hand; (3) another fasciculus which goes dorso-mesad, almost vertically in the brain, to join the ends of the pre- and postcentral gyri at the top of the hemisphere, and their continuation upon its mesal aspect known as the paracentral lobule, centre and fasciculus for movements of the opposite foot and leg. Besides these three great cortical areas and their connected fasciculi of nerve-fibres, which go to make up the pyramidal tract, we recognize (4) a cortical centre for speech movement of the tongue and lips in the base of the left third frontal gyrus over the fissure of Sylvius (Broca's speech-centre), with a connected white fasciculus which passes into the elbow of the internal capsule, and can be traced (by means of secondary degeneration) into the inner part of the base of the crus and into the pons, but not to the pyramid. Another probable centre (5), for coarse lingual movements and for the various movements of deglutition, is in the folds of the insula, its fasciculus not joining the pyramid.
FIG. 9.
Longitudinal (sagittal) Section through the Brain, to show the distribution of the fasciculi of the internal capsule. Fasciculi of motor tract in dotted lines, to fronto-parietal convolutions. Fasciculi of sensory tract in full lines, to temporo-parieto-occipital convolutions: N. C., nucleus caudatus; N. L., nucleus lentiformis; T. O., thalamus opticus. 1, level of crus cerebri; 2, level of pons; 3, level of oblongata. (This diagram is to be used in conjunction with [Fig. 7.])