I340 A MANUAL OF ANATOMY 



The grey matter which forms it is perforated by openings for the 

 passage of the postero-mesial branches of the posterior cerebral 

 arteries. 



The corpora albicantia or mammillaria are situated directly in 

 front of the locus perforatus posticus, and present the appearance 

 of small, white, pea-like bodies, lying close to the median line. 



The tuber cinereum extends from the corpora albicantia to the 

 optic commissure, and is composed of grey matter. The in- 

 fundibulum is connected with the tuber cinereum close behind the 

 optic commissure, and passes downwards to the posterior part of 

 the pituitary body. 



The locus perforatus anticus of each side coincides with the 

 vallecula Sylvii at the inner end of the stem of the fissure of 

 Sylvius. It lies outside the interpeduncular space, close to the 

 outer aspect of the optic commissure. It consists of grey matter, 

 which is perforated by openings for the passage of a few antero- 

 mesial branches of the anterior cerebral artery, and numerous 

 antero -lateral branches of the middle cerebral artery. These 

 branches are destined for the nucleus caudatus and nucleus lenticu- 

 laris of the corpus striatum, the grey matter of which nuclei comes 

 to the surface of the brain at the locus perforatus anticus. 



The medulla oblongata and pons Varolii occupy the basilar groove 

 of the interior of the base of the skull ; the cerebellar hemispheres 

 occupy the cerebellar fossae of the occipital bone ; the temporal 

 lobes of the cerebrum sink deeply into the lateral divisions of the 

 middle fossa of the base of the skull ; the orbital surfaces of the 

 frontal lobes occupy the lateral divisions of the anterior fossa ; 

 the stem of the fissure of Sylvius faces the posterior or Sylvian 

 border of the small wing of the sphenoid ; the optic commissure 

 rests upon the olivary eminence and optic groove of the sphenoid ; 

 and the olfactory bulb rests upon one half of the cribriform plate 

 of the ethmoid bone. 



Superficial or Surface Origins of the Cranial Nerves. 



The first or olfactory nerve occupies the following positions 

 The olfactory bulb and olfactory tract occupy the olfactory sulcus 

 on the orbital surface of the frontal lobe, near the great longitudinal 

 fissure ; and the olfactory filaments pass through the foramina of the 

 cribriform plate of the ethmoid bone on their way from the olfactory 

 cells of the olfactory mucous membrane to the olfactory bulb. 

 Posteriorly the olfactory tract divides into two roots, mesial and 

 lateral. The mesial root curves inwards behind the area of Broca 

 to the callosal gyrus. The lateral root passes backwards and out- 

 wards across the outer part of the locus perforatus anticus. The 

 triangular area of grey matter, which is situated between the 

 diverging roots of the olfactory tract, is called the trigonum oljac- 

 torium. It is sometimes spoken of as the middle or grey root of the 

 olfactory tract. The area of Broca is situated in front of the mesial 



