The neuroanatomic or neuropathologic basis of Gilles de la Tourette's syndrome (GTS) remains unknown. Recent studies have suggested abnormalities of cerebral asymmetry and basal ganglia volumes. We studied 17 patients with GTS and eight normal controls using volumetric MRI techniques for measuring the caudate nucleus, amygdala, and corpus callosum. One subject with GTS was subsequently excluded because he was left handed. No absolute differences in caudate nucleus volumes between patient and control groups were evident. There was an increase in corpus callosum (CC) cross-sectional area and a loss of the normal asymmetry of the caudate nucleus in the patient group. A loss of the normal correlation between cross-sectional area of the CC and whole brain index (WBI) in the patient group also was found. The amygdala measurements had a poor interrater reliability.

The fundamental mechanism by which the cat is able to right itself seems to develop very early. The first simple movement in the 16-mm. embryo is a ventrolateral flexion of the head, and rotation is soon added to this (Windle and Griffin, '31). Although the development of the righting mechanism is thought to be traceable to these primitive responses, the purposeful act of righting is not actually accomplished until later in fctal life. At the end of thc third o r beginning of the fourth fetal quarter kittens often rotate the head into a position in which the chin is parallel to the surface upon which they are lying. This is thought to be accomplished by chance in specimens 75 mm. and 80 mm. long. Fetuses 95 mm. and 100 mm. long, on the other hand, seem to exhibit the righting reaction in a very immature form; the motor mechanism seems to be too poorly developed to complete the actions that are initiated. At a slightly later stage (110 mm.) the righting phenomenon is often imperfectly completed, but it is well developed at birth. The majority of kittens measure about 135 mm. o r 140 mm. crown-rump length at the time of birth, which is supposed to be a t the end of the eighth week, but may be a t the sixty-second or sixtyfourth day (Craig, '12).Magnus ('24) has shown that the act of righting may be initiated by afferent impulses arising not only in the vestibular mechanism, hut also in the end organs of the skin and muscles of the trunk and neck, and, in the higher mammals, Contribution no. 160. 85

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