422 ANATOMICAL TECHNOLOGY. 



By placing the bead of the bristle, or the tip of the tracer or 

 syringotome, in the cephalic part of the diacoelia, note that the roof, 

 diatela, is partly membranous and partly formed by the thickening 

 known as the conarium ( 1084). 



Then slice away the thalami to a still lower level so as to expose 

 the diacoelian floor. Note that it is depressed, and bounded caudad 

 and cephalad by transverse ridges ; also that there are no plexuses 

 therein. 



Slice off both hemispheres to the level of the conarium. Then 

 remove another slice, including the conarium and the aulatela upon 

 which it rests. This will expose a wedge-shaped cavity, the aula, 

 which is bounded as follows : caudad, by the ridge mentioned 

 above as the cephalic boundary of the diacoelia ; laterad, by the 

 port(B whose length nearly coincides with its own ; cephalad, by the 

 terma, a lamina of nervous tissue uniting the mesal walls of the 

 hemispheres at the cephalic end of the portse ; (the terma is more 

 easily seen if the left L. ol. and cephalic end of the hemisphere 

 are gently pushed away from the right) ; dorsad, by the aulatela, 

 the atrophied continuation of the terma. 



If the mesal wall of the left hemisphere be removed, the extent 

 and form of the right porta may be seen. 



1097. With Menobranchus the conditions are so different as 

 to require special directions : 



Introduce a scissors blade just caudad of the cerebellum on 

 either side, and cut cephalad to the caudal end of the hemisphere ; 

 do the same on the other side, and turn the flap so formed cephalad 

 upon the hemispheres. This exposes the epi-, meso- and diacoelia. 

 Note that the lateral walls are thicker than the roof, and that the 

 eutal surface of the roof presents a slight transverse ridge which 

 indicates the division between the diencephalon and the mesen- 

 cephalon. 



The floor of the mesocoelia is nearly level, and its cephalic mar- 

 gin overhangs the passage the canal of the infundibulum leading 

 to the hypophysis. 



In the diacoelia lie side by side a pair of string-like plexuses the 

 diaplexuses which are attached to the aulatela or diatela and ex- 

 tend the whole length of the cavity. They should be drawn to the 

 sides or cut off, but not pulled upon at all. The floor of the diacoelia 

 is then seen to be irregular, sloping from each side to a mesal furrow. 



