80 



PSYCHOBIOLOGY 



the brain stem. These groups are called nuclei, and most of these nuclei 

 have received distinctive names. 



In addition to the substances of the brain, it is important to distinguish 

 the cavities or ventricles, since it is often convenient to refer to the 

 position of a nucleus or other detail as being in the wall of a certain ven- 

 tricle, although the cavity may be relatively very small as compared with 

 the thickness of the so-called ' walls '. In another respect the cavities 

 are important, since the brain and cord are formed from a single tube, 

 which, in the foetus, has a relatively large bore and thin walls, the brain 

 and cord proper forming by actual thickening of these walls. 



Bui bus olfactorius 

 Tract us olfactorius 

 Chiasms opticum 



N. oplicu: 



Trtgonum olfactorium 

 TracLus opticus 



N oculomotoriu 



N. trochlears 

 N Irigcmin 



N. accessorial 



N.bypogtossus /' 



N. spinalis I. 



Polos frontalis 



Fissura lungiiudinalis' cerebri 

 Sulcus olfactorius 



Hypophysis 



cerebri lateralis 

 (Sylvii) 



Polus temporalis 



Substantia perforata 

 anterior 



lnfundibulum 

 . Tuber cinereum 

 L. Corpus roamillare 



Fossa interpedim- 

 cularis (Tarini) 



- Peduncultu 

 cerebri 



Pons (Varoli) 



Flocculus 



Pleaus chorioideus 

 ■i ventriculi quarti 



Foramen caecum 

 Hemisphaerium cerebelli 

 Medulla oblongata 

 Decussltio pyramidum 



Medulla spinalis 

 'Polus occipitalis 



Fig. 68. Brain viewed from the front and below, one-half natural size. (Toldt, 

 Anaiomischer Atlas.) 



The cavities of the brain are as follows : 



First and second ventricles (ventriculi laterales) : hollows within 

 the right and left cerebral hemispheres respectively [Fig. 70]. .Third 

 ventricle (ventriculus tertias), lying between the optic thalami, the inner 

 surfaces of which form its side walls [Fig. 66]. The * floor ' or ventral 

 boundary is formed by the tuber cinereum, the corpora ma mil! aria, the 



