XIII.] THE FKOG. !■; 



are found in the viscera and vessels. An account of the di 

 position of the muscles in the hind-limb will be found in tl 

 Laboratory work. 



The nervous system is conveniently divisible into tv 

 parts, the cerebrospinal and the sympathetic. The cerebr 

 spinal nervous system again consists of the brain, or encephi 

 Ion, with its nerves, and the spinal cord, or myelon, with i 

 nerves. 



The encephalon lies in the cranial cavity, which it near 

 fills, and is divisible into the hind-brain, the mid-brain ai 

 the fore-brain, which last again comprises three division 

 the thalamencephalon, the cerebral hemispheres, and tl 

 olfactory lobes. 



The greater part of the hind-brain is formed by tl 

 medulla oblongata, which is the continuation of the myelc 

 forwards and presents, on its dorsal aspect, a triangular cavit 

 the apex of which is directed backwards. It is roofed ov 

 by a thick and very vascular membrane (choroid plexus), tl 

 inner surface of which presents transverse folds on either sic 

 of a median longitudinal ridge. The cavity is the four 

 ventricle ; it communicates behind with the central canal 

 the myelon, while, in front, it narrows into a passage whi( 

 connects the fourth ventricle with the cavities anterior to : 

 The thick lateral ridges of nervous substance at the sid 

 of the fourth ventricle, which represent the restiform bodu 

 pass, in front, into the outer extremities of a short bro£ 

 tongue-shaped plate, convex ventrally and concave dorsall 

 which overhangs the anterior part of the fourth ventricl 

 and is the cerebellwm. 



In front of this, the dorsal moiety of the mid-brain 

 formed by two oval bodies, the long axes of which a: 

 directed inwards and backwards. These are the optic lobe 

 When laid open, each is seen to contain a cavity or ventric 

 with an opening on its inner face. These openings lead in 

 M. 12 



