NEUROLOGY 





The hypophysis (pituitary body} (Fig. 721) is a reddish-gray, somewhat oval 

 mass, measuring about 12.5 mm. in its transverse, and about 8 mm. in its antero- 

 posterior diameter. It is attached to the end of the infundibulum, and is situated 

 in the fossa hypophyseos of the sphenoidal bone, where it is retained by a circular 

 fold of dura mater, the diaphragma sella; this fold almost completely roofs in the 

 fossa, leaving only a small central aperture through which the infundibulum passes. 



Anterior Optic 

 commissure recess 



Ant. cerebral artery - 



Optic chiasma. 



^Infundibulum 



W3*. 



'.'.Cerebral peduncle 



Corpus mammiUare 

 Post, cerebral artery 

 Basilar artery 



Pans 



Anterior lobe,, 

 of hypophysis 



Posterior lobe 



FIG. 721. The hypophysis cerebri, in position. 



Shown in sagittal section. 



Optic Chiasma (chiasma opticum; optic commissure}. The optic chiasma is a 

 flattened, somewhat quadrilateral band of fibers, situated at the junction of the 

 floor and anterior wall of the third ventricle. Most of its fibers have their origins 

 in the retina, and reach the chiasma through the optic nerves, which are continuous 

 with its antero-lateral angles. In the chiasma, they undergo a partial decussation 

 (Fig. 722) ; the fibers from the nasal half of the retina decussate and enter the optic 

 tract of the opposite side, while the fibers from the temporal half of the retina do 

 not undergo decussation, but pass back into the optic tract of the same side. 

 Occupying the posterior part of the commissure, however, is a strand of fibers, 

 the commissure of Gudden, which is not derived from the optic nerves; it forms a 

 connecting link between the medial geniculate bodies. 



Optic Tracts. The optic tracts are continued backward and lateral ward from 

 the postero-lateral angles of the optic chiasma. Each passes between the anterior 

 perforated substance and the tuber cinereum, and, winding around the ventro- 

 lateral aspect of the cerebral peduncle, divides into a medial and a lateral root. 

 The former comprises the fibers of Gudden's commissure. The lateral root consists 

 mainly of afferent fibers which arise in the retina and undergo partial decussation 

 in the optic chiasma, as described; but it also contains a few fine efferent fibers 

 which have their origins in the brain and their terminations in the retina. When 

 traced backward, the afferent fibers of the lateral root are found to end in the lateral 

 geniculate body and pulvinar of the thalamus, and in the superior colliculus; and 

 these three structures constitute the lower visual centers. Fibers arise from the 

 nerve cells in these centers and pass through the occipital part of the internal 

 capsule, under the name of the optic radiations, to the cortex of the occipital lobe 

 of the cerebrum, where the higher or cortical visual center is situated. Some of the 

 fibers of the optic radiations take an opposite course, arising from the cells of the 

 occipital cortex and passing to the lower visual centers. Some fibers are detached 

 from the optic tract, and pass through the cerebral peduncle to the nucleus of 

 the oculomotor nerve. These may be regarded as the afferent branches for the 



