II28 



HUMAN ANATOMY. 



as a circular area of gray matter enclosed by a zone of cerebello-thalamic fibres ; 

 farther forward it, too, gradually diminishes and disappears at a level somewhat 

 behind that of the corpora mammillaria. The connections of the red nucleus have 

 been considered in connection with the superior cerebellar peduncle (page 1095) ; 

 suffice it here to recall its twofold significance as an interruption station for many 

 of the cerebello-rubro-spinal and for the cerebro-rubro-spinal tracts. 



The corpus subthalamicum (nucleus hypothalamicus), or nucleus of Lnys, is a 

 mass of deeply tinted gray matter peculiar to the subthalamic region and unrepresented 

 in the mid-brain. It appears in cross-section (Fig. 970) as a small biconvex area, 

 immediately dorsal to the tract of crustal fibres and lateral to the red nucleus and the 

 substantia nigra. As the latter diminishes, the subthalamic nucleus expands to take 

 its place and, where fully represented, measures from 3-4 mm. in thickness and from 

 10-12 mm. in its longest diameter, and extends superiorly considerably beyond the 

 level of the red nucleus. Histologically the subthalamic body is distinguished by a 

 dense net-work of fine medullated nerve-fibres, enclosing pigmented multipolar nerve- 

 ' cells of medium size, and by an unusually close mesh- work of capillary blood-vessels. 

 The dorsal surface of the nucleus is defined by the overlying lateral part of the field 



Fig. 976. 



Septum lucidum 

 Choroid plexus 



Foramen oi Monro 

 Genu of corpus callosiim 



Rostrum of 

 corpus callosum 



Anterior commissure 



Lamina cinerea" 



Optic recess' 



Body of fornix 

 Velum interpositum coveriusJ^ 

 Thalamus, [thalamus 

 mesial surface 



Taenia thalami 

 plenium 



Commissura habenulae 

 Pineal recess 



Optic commissure 



Anterior lobe of pituitary bod^ 

 Posterior lobe of pftuitafy 



Infundibulum 



Pineal body 



Posterior commissure 



■Quadrigeminal plate 

 \ Sylvian aqueduct 



V \ Cerebral peduncle 

 \ Middle commissure 

 Sulcus hypothalamicus 

 Mammillary fcody 

 Anterior pillar of fornix 

 Tuber cinereum 



Right lateral wall of third ventricle : velum interpositum covers superior surface of thalamus. 



of Forel, as the stream of fibres passing between the red nucleus and the thalamus 

 and the internal capsule is called. From the ventral surface of the nucleus, fibres 

 pierce the adjacent crusta and join the ansa lenticularis to gain, probably, the globus 

 pallidus ; other perforating fibres perhaps connect the subthalamic body with 

 Meynert's and Gudden's commissures (Obersteiner). The ventro-medial ends 

 of the bodies of the two sides are connected by a bridge, the commissura 

 hypothalamica, which traverses the fioor of the third ventricle above the 

 mammillary bodies. In addition to connecting the two subthalamic nuclei, the 

 commissure contains decussating fibres from the anterior pillars of the fornix and, 

 according to Edinger, probably fibres from the fore-end of the posterior longitudinal 

 fasciculus. 



The corpora mammillaria (corpora mamillaria), also called the corpora albi- 

 cantm, are two hemispherical elevations, about 5 mm. in diameter, which lie close to the 

 mid-line within the interpeduncular space on the basal surface of the brain (Fig. 993). 

 They are almost but not quite in contact, being separated by a narrow interval which 

 immediately behind the little bodies deepens into the anterior recess marking the 

 front end of the shallow median furrow that grooves the posterior perforated sub- 

 stance. The posterior surfaces of the mammillary bodies indicate the anterior limit 

 of the ventral surface of the mid-brain. When examined in section (Fig. 970), 



