614 PHYSIOLOGY OF THE BRAIN-STEM 



Besides, it is very probable that the optic-nerve fibers entering the anterior 

 corpora quadrigemina play a considerable part in the reflex excitation of the 

 nuclei of the eye muscles located along the floor of the aqueduct of Sylvius. 

 The fact that in the monkey, at least, these fibers end in large numbers under 

 and about the aqueduct, and the results of electrical stimulation both favor 

 this view. By stimulating the anterior body of the dog, Adamuk obtained 

 the following movements of the eyes: stimulating on the right side of one 

 body, movement of both eyes to the left; stimulating in the midline, parallel 

 movement of both eyes directly upward ; stimulating the posterior side, simul- 

 taneous movements downward and inward. Movements of the iris were also 

 observed. After a sagittal section in the median plane, only the eye on the 

 same side was moved. Ferrier has made observations similar to these on 

 the monkey. 



Some clinical observations indicate that the posterior corpora quadrigemina 

 are concerned in the propagation of auditory impressions, the hearing in the 

 opposite ear being affected in cases where this part is diseased. Bechterew 

 and Flechsig assert, in agreement with this view, that the ganglion of the 

 posterior body receives fibers by way of the lateral fillet, from the cochlear 

 nerve, and v. Monakow has shown that the internal geniculate body is abun- 

 dantly connected with the posterior quadrigeminal body and sends fibers to the 

 cortex of the temporal lobe. The statements that stimulation of the posterior 

 body in dogs and monkeys evokes a cry from the animal, and that production 

 of voice is stopped by section of that body, lend some weight also. 



B. THE CRURA CEREBRI 



The crura cerebri, or more correctly the gray matter which forms the wall 

 of the aqueduct of Sylvius, is of special interest mainly because the nuclei 

 of the oculo motor and trochlear nerves are found there. 



Fig. 272 represents in a frontal section the nuclei of the oculo motor as made 

 out by Bernheimer. It is evident that this nucleus consists of several parts, 

 namely, a lateral chief nucleus, a median nucleus with small cells (Ke M) and 

 an unpaired median nucleus with large cells (Gr Mk). It is evident from the 

 figure also that the nerve roots connected with the nucleus are in part crossed. 



By successive and complete removal of the extrinsic and intrinsic eye mus- 

 cles innervated by the oculo motor, and by a study of the resulting changes in 

 the nucleus, Bernheimer has reached the following conclusions with regard to 

 the function of its different parts (Fig. 273) : The extrinsic muscles are inner- 

 vated by the lateral chief nucleus, but its cells are not grouped into sharply 

 divided individual nuclei. The small-celled median nuclei (Ke M, Fig. 

 272) supply the intrinsic muscles of the homolateral eye, and the large-celled 

 median nucleus (Gr Mk, Fig. 272) belongs to the intrinsic muscles of both 

 eyes. 



v. Monakow has made some clinical observations as to the relations of 

 these parts in man, but at present the only conclusions that can be drawn 

 are that the intrinsic muscles (ciliary muscle and the muscles of the iris) 

 are represented in the extreme anterior end of the nucleus, and the extrinsic 

 muscles in the remaining divisions. 



