When these cortical areas are destroyed by disease, or when their connected fasciculi are severed, secondary degeneration takes place and extends to the end of the respective bundles, even to the lower extremity of the spinal cord. Before leaving the subject of the composition of the kinesodic system it is desirable to add a few words concerning the decussation of the pyramids or distribution of the pyramidal tract in the spinal cord. As is well known, this is double, a small part of the pyramidal bundle remaining on the same side of the median line, the so-called direct pyramidal fasciculus or column of Türck (Fig. 5, No. 11) forming the mesal edge of the anterior column of the cord. The larger part of the pyramid crosses the median line at the decussation, and enters the opposite lateral half of the cord, in which it is found as the crossed pyramidal fasciculus (Fig. 5, No. 10) in the posterior part of the lateral column, rapidly diminishing in size in the dorso-lumbar part of the cord. The {88} important point to bear in mind for the study of monoplegias and of hemiplegia is that the amount of decussation is far from uniform. This variability was first demonstrated by Flechsig.[14] He found in a series of sixty fœtuses such variations in the relation of the crossed and direct fasciculi as 100:0 (complete decussation), 92:8, 84:16, 70:30, 52:48 (nearly semi-decussation, producing equal fasciculi), 35:65, 10:90 (almost non-decussation). [Footnote 14: _Die Leitungsbahnen im Gehirn und Rückenmark des Menschen_, Leipzig, 1876.] It should also be added that quite certainly the cerebellum, nucleus caudatus, nucleus lentiformis, and nucleus pontis form parts of the complete kinesodic system, but we are as yet ignorant of their exact connections and functions. With respect to the anterior part of the frontal lobe, forward of the oblique line A B across Figs. 10 and 11, the study of human cases of destructive injury and disease would indicate that it is not associated either with the kinesodic or with the æsthesodic systems. The SYMPTOMS of lesions of the kinesodic system, particularly of the pyramidal tract, are exclusively motor, consisting of spasm and paralysis. Contracture of the paralyzed parts follows the paralysis after a few weeks if the lesion be a destructive one. Clinically, the following DIAGNOSES of localization of lesions in this system are now possible: (_a_) Lesion of the speech-centre (4) and of its associated white fasciculus is indicated by intermittent or constant aphasia of the motor form, with or without paralysis of the face and limbs (on right side usually). (_b_) Lesion of the facial centre (1) and of its associated fasciculus is characterized by the occurrence of spasm or paralysis, or of both in rapid succession, in the facial muscles; their electrical reactions remaining normal.