OPHTHALMOPLEGIA. 191 



with the nuclei for the eye muscles. (Fig. 14, p. 183.) The 

 track from the cortex is supposed to pass through the internal 

 capsule near its genu, and thence to the nuclei through the 

 mesial third of the basal portion of the crus cerebri. Supra- 

 nuclear lesions do not produce isolated ocular paralyses, but 

 manifest themselves by temporary conjugate deviations of the 

 eyes. The crus cerebri, however, is traversed by the rootlets of 

 the third nerve on their way out from the adjacent nuclei, and 

 consequently the paralysis produced by lesions of this part of the 

 brain are of a nuclear or infranculear type. 



Nuclear Ophthalmoplegia. The nucleus of the third nerve is 

 compound, its total length being about a third of an inch. Its 

 anterior part encroaches on the floor of the third ventricle, and 

 its posterior or lower limit corresponds to the groove between 

 the anterior and posterior quadrigeminal bodies. Degenerative 

 nuclear disease, such as, for example, results from syphilis, may 

 pick out portions of the compound nucleus, producing paralysis 

 of isolated muscles or of specially associated ocular movements. 

 Such isolated paralyses as loss of accommodation, loss of the 

 pupil contraction which normally accompanies convergence of 

 the eyes, loss of convergence and accommodation although the 

 internal recti still act in conjugate movements, and paralysis of 

 a single extraocular muscle, are examples of this selective action. 

 The most familiar example of all is the Argyll Eobertson pupil, in 

 which myosis and loss of light reflex co-exist. It is true that the 

 usual explanation of this double phenomenon is that the myosis 

 is due to a lesion of the fibres of the cervical sympathetic in some 

 part of their course through the central nervous system before 

 emerging by the cervical roots, and that the failure to react to 

 light is due to a lesion of Meynert's fibres which pass between 

 the superior corpora quadrigemina and the nucleus of the third 

 nerve. It is possible, however, that actual degeneration of a 

 part of the third nucleus can produce both phenomena. The 

 ophthalmoplegia of nuclear disease may be very extensive and 

 is often bilateral. Weakness of the orbicularis palpebrarum is 

 sometimes associated with ophthalmoplegia, leading to the 



