82 ANATOMY OF A CHELONIAN, 



been seen hitherto^ as it is apt to be removed in prepar- 

 ing the skeleton (28). Cut it away, with those orbital 

 muscles which arise from the floor of the brain cavity, 

 and expose the optic nerves. 



206. Clear away the dura mater which closely in- 

 vests the exposed ventral part of the cord and of the 

 mid-brain. Then study the general outline of the brain 

 as now seen from its ventral aspect. Note: 



a. In front, the olfactory lobes (170). 



b. Behind them, in the middle line, the optic com- 

 missure, from which the optic nei'ves diverge an- 

 teriorly and the optic tracts behind. 



c. Between the optic tracts, thQ pituitary body or 

 hypophysis cerebri. 



d. Meeting at the base of the olfactory lobes in 

 front, but diverging behind, so as to embrace 

 between them the pituitary body and optic 

 tracts, the large prosencephalic lobes {^cerebral 

 hemispheres). 



e. Between these, bearing the infiindibuluin, or 

 stalk of the pituitary body, and bounded by 

 the optic commissure in front, is the ventral 

 aspect of the thalamencephalon. 



f. On the sides of the thalamencephalon, and 

 passing dorsally beneath the optic tracts, are 

 the crura cerebri^ forming the ventral portion 

 of the mid-brain. 



g. Behind the mid-brain are the ante?'ior pyramids 

 of the medulla oblongata^ with a furrow between 

 them, continuous behind with the anterior fis- 

 sure of the spinal cord. 



//. Dorsal to the medulla, and projecting slightly 



