xIV NERVOUS SYSTEM 369 
less complicated, and perhaps even more interesting from a 
morphological standpoint, are the structures arising out of the 
thalamencephalon. By thickenings of its lateral walls two large 
ganglia, the optic thalami, are formed, and on the inner or dorsal 
aspect of each of these a ganglion habenulae is developed. From 
F.B M.B H.B 
eam ee 
ch pr Lh op. i 
Ore 
NS 
Fic. 210.—Diagram of the general structure of the brain in Craniates. A, vertical 
longitudinal section ; B, dorsal view showing the brain cavities on the right side. 
c, Cerebellum ; c.c, central canal of the spinal cord ; ¢., cerebral hemispheres 3 c.s, 
corpus striatum ; F.B, fore-brain ; fm, foramen of Munro; #., hind-brain ; in, 
infundibulum ; Z.v, lateral ventricle ; m, mesocoele ; M.B, mid-brain ; m.o, medulla 
oblongata ; 0./, olfactory lobe; op./, optic lobe; op.t, optic thalamus; p, para- 
physis ; pc, prosocoele; pm.o, pineal organ; p.o, parietal organ; pr, prosen- 
cephalon ; pé, pituitary body ; rf, rhinocoele ; sp.c, spinal cord; s.v, saccus vascu- 
losus ; th, thalamencephalon ; iii, iv, third and fourth ventricles, (After Parker 
and Haswell.) 
_the sides of the thalamencephalon the primary optic vesicles are 
derived, which later become transformed into the retinal parts 
of the paired eyes and the optic nerves. Besides the optic 
vesicles there is a second pair of embryonic outgrowths which 
arise from the roof of the thalamencephalon. These outgrowths 
form stalked vesicles and represent a pair of degenerate visual 
VOL. VII 2B 
