ANATOMY IX A NUTSHELL. 



357 



The cerebellum is called the arbor-vita 1 or tree of life. It is the center for 

 the control of muscles. It is between the corpora qnadrigemina in front and 

 the medulla oblongata behind, and forming part of the roof of the fourth ven- 

 tricle. 



The pons, also called pons Varolii and pons cerebelli, is a great transverse 

 commissure seen at the base of the brain in front of the medulla. Its fibres 

 connect the hemispheres of the cerebellum with each other and the medulla. 



The medulla oblongata is (a) marrow; (b) the so-called spinal nervous sys- 

 tem; the myelon; more fully called medulla spinalis: (c) the hindmost segment 

 of the brain, continuous with the spinal cord. 



PLATE CLXXVII. 



area supplied by middle cerebral artery. 

 Showing Blood Supply at Base of Brain. 



A ventricle (literally a belly, a stomach) is a small cavity. Those of the 

 brain are a series of connecting cavities, containing fluids, within the brain, 

 continuous with the central cavity of the spinal cord. They are the remains 

 of the original neural canal, formed by a folding over of the epiblast. 



The optic commissure or chiasma, somewhat quadrilateral in form, rests 

 upon the optic groove of the sphenoid bone, being bounded, above, by the 

 lamina cinerea; behind, by the tuber cinereum; on either side, by the anterior 

 perforated -pace. Within the commissure the optic nerves of the two sides 

 undergo a partial decussation. The fibres which form the inner margin (in- 

 ferior commissure of Gudden) of each trad are continuous across from one to 

 the other side of the brain. These may be regarded as commissural fibres 

 (intercerebral) between the interna] geniculate bodies. Some fibres are con- 

 tinued across the anterior border of the chiasma, and connect the optic uerves 

 of the two sides, having no relation with the optic tracts. They may be re- 

 garded as commissural fibres between the two retinae (inter-retinal fibres'). 

 The outer fibres of each tract are continued into the optic nerve of the -nine side. 



