194 



ELEMENTS OF MAMMALIAN ANATOMY. 



largest ventricles of the brain. In order to view them 

 satisfactorily, the entire dorsal portion of the brain down 

 to the corpus callosum must be cut away, and a hole 

 cut through the corpus callosum. A number of cross- 

 sections of the cerebral hemispheres should also be 

 studied. 



FIG. 92. SAGITTAL SECTION OF THE BRAIN. 



ac, Anterior commissure ; ai), arbor vitae ; c, habena ; cc, canalis centralis ; 

 cb, cerebellum; cm, middle commissure or massa intermedia; cr, 

 sulcus crucialis; cpq, corpus quadrigemina ; ex, choroid plexus of 

 third ventricle the dark line dorsad of ex is the velum interpositum ; 

 /, sulcus splenialis ; fr, frontal lobe of cerebrum ; fn, anterior pillars 

 of the fornix; in, infundibulum ; it, iter, or aqueduct of Sylvius; k, 

 genu of corpus callosum; Imx, lamina terminalis; m, splenium; mr, 

 sulcus marginalis ; med, medulla ; op, optic chiasm ; oc, occipital lobe ; 

 ol, olfactory lobe; pn, pineal gland; po, pons Varolii; pc, posterior 

 commissure; pv, inferior medullary velum; pvv, superior medullary 

 velum or valve of Vieussens ; 3 and 4, third and fourth ventricles. 



Each ventricle is composed of a body from which pro- 

 jects an anterior cornu and a middle or descending cornu. 

 The former extends into the frontal lobe and thence into 

 the olfactory lobe, and the latter descends into the 

 temporal lobe. The roof of the body of the lateral ven- 

 tricle is formed by the corpus callosum (Figs. 92, 93, 

 and 94) and the mesal wall by the septum lucidum, a 



