BASAL GREY COMMISSURE 



707 



grey matter of tlie tegmenta of the crura cerebri, and is attaclied in front to the 

 corpora allncantia. The portion of the space which is situated in front of the exit 

 of the third nerve forms part of the floor of the third ventricle; the posterior part 

 belongs to the mesencephalon. 



The corpora albicantia appear as a pair of white knobs in the base of the 

 brain. Each contains in its interior a grey nucleus. This nucleus is joined b}' the 

 anterior ]nllar of the fornix and the l)undle of Vicq d' Azyr of the same side. The 

 bundle of Vicq d'Azyr passes upwards and forwards through the grey matter of 

 the optic thalamus to the anterior tubercle of that body. 



The tuber cinereum is a gre}^ elevation placed inmiediately behind the optic 

 commissure. It is the largest part of the basal grey commissure, and is continuous 

 laterally, above the optic tracts, with the grey cortex of the temporal lobes (fig. 421). 

 In front it passes over the optic commissure into the lamina cinerea. It is con- 

 tinued below into a conical process, the infundibulum, which is directed down- 

 wards and slightly forwards, through the central opening in the diaphragma 

 selloe to end in the posterior lobe of the pituitary body. The upper part of the 

 infundibulum is hollowed out by a diverticulum of the third ventricle, the recessus 



Fig. 423. 



-Coronal Sectiox through the Third Ventricle behind the Middle 

 OoiMiS'^rKK. (Gegeabaur. 



CORPUS CALLOSUM 



FORNIX 



OPTIC THALAMUS 



MIDDLE COMMISSURE 



suBSTAxrn xigra 



CRUST A 



An> .J** 



CA UDA TE NUCLEUS 

 LATERAL 

 VENTRICLE 



CLAUSTRUM 



LENTICULAR 



NUCLEUS 

 RED NUCLEUS 



■/ FIMBRIA 



infundibuli. The tuber cinereum and infundibulum correspond to the median 

 recess in the floor of the third venlrirlc. 



The pituitary body, or hypophysis cerebri, is a small ellipsoidal body which 

 is lodged in the pituitary fossa of the sphenoid bone. Its long axis is directed 

 transversely, and its antero-posterior and vertical diameters are about equal. 



Tlie pituitar}' body consists of two distinct lobes, an anterior and a posterior. The anterior 

 lobe is of a reddish-gre.v colour, and is considerably larger than the i)Osteiior lobe, which it ]iai- 

 tially embraces. The posterior lobe, of a yellowish-grey colour, is lodged in a recess in the anterior 

 lobe, and is the only part connected with the infuiKlibulum. 



This body was formerly described as the pituitary gland, because it was suppo.sed to secrete 

 the pituita, or mucus of the nose. According to Gaskell's ingenious theory, the infundibulum is 

 the mouth of an archaic alimentary canal. The ventricular system of the brain is the mdiment 

 of the c^eiihalic stomach as found in Arthrojjods. The central Ciinal of the spinal cord is the 

 archaic intestine, and the neuro-enteric canal (an cmbrj^onic communication between the neural 

 tube and the intestine) connects this archaic intestine with the ano-rectal )-egion. This pituitary 

 body is of great interest in the light of this theory, as it livings the archaic mouth to the surface. 

 The jiosterior lobe is developed in coiniection with the brain, but the anterior lobe is formed inde- 

 pendently. It originates as an upward growth of the epiblastic invagination which forms the 

 mouth, and is atterwards cut off by the chondrification and subsequent ossification of the skull. 



