THE BASE OF THE FORE-BRAIN. 85 



has an internal secretion which appears to have an inhibitive 

 action on growth and has been found diseased in acromegalia. 



Corpora Mammillaria (Figs. 21 and 26). Two white bodies 

 (corpora albicantia), as large as a small pea, are situated one on 

 either side of the median line, between the tuber cinereum and 

 the pigmented gray matter of the posterior perforated substance. 

 Each is formed superficially by a loop in the columna of the fornix 

 and is, tfierefore, composed of white substance at the surface. 

 There is gray matter in the interior which forms a medial and a 

 lateral nucleus (Fig. 46). In the medial nucleus the fornix fibers 

 terminate and an ascending bundle rises, called the fasciculus 

 thalamo-mammillaris (Vicq d'Azyri). The latter terminates in 

 the anterior nucleus of the thalamus. From the medial nucleus 

 of the corpus mamillare also rises the tegmental part of the fascic- 

 ulus pedunculo-mammillaris; the basilar portion of the same 

 bundle rises in the lateral nucleus and both parts of this pedunculo- 

 mammillary bundle run downward into the mid-brain to an 

 unknown termination. 



Immediately behind the corpora mammillaria is the posterior 

 perforated substance (Figs. 21 and 26). This is the exposed 

 part of the substantia nigra of the mid-brain, perforated for the 

 passage of the postero-median ganglionic arteries. The pons 

 and bases pedunculi bound it behind. Issuing from the inner 

 side of the basis pedunculi is the large oculomotor nerve; and 

 coursing over its surface from . behind forward, is the smaller 

 trochlear nerve. The bases pedunculi will be described with 

 the mid-brain to which they belong. 



FISSURES OF THE MEDIAL AND TENTORIAL SURFACE. 



To expose the medial surface of the cerebral hemispheres^ a 

 median sagittal section must be made through the connecting 

 links of the hemispheres and the inter-brain, dividing the fore- 

 brain into lateral halves. Separate the lips of the longitudinal 

 fissure of the cerebrum; drop the moistened brain- knife down 

 onto the corpus callosum; and make one quick sweep of the 

 knife toward you. Of the surface now exposed the middle one- 

 third is produced by section. 



