158 



COMPARATIVE ANATOMY 



covered by a thickened and vascular portion of the pia mater or 

 choroid plexus. 



. m\v\v 



^- YE VI H 



If L.ol 



Hyp 



FIG. 129. BRAIN OF LARVAL LAMPREY. (A, from above ; B, from below ; 

 C, from the side.) 



yjj (Bas.G), cerebral hemispheres, between which, in A, the median portion of the 

 prosencephalon is seen, with the membranous roof removed ; L.ol, olfactory 

 lobe ; ZH, thalamencephalon ; G.p, pineal body ; Hyp, hypophysis ; 8v, 

 saccus vasculosus ; MH, mid-brain ; HH, cerebellum ; Nil, medulla obi on - 

 gata ; Med, spinal cord ; I-X, cranial nerves ; XII, first spinal nerve (hypo- 

 glossal). 



The brain of Myxine shows many special peculiarities : its 

 subdivisions are broader and more closely approximated than in 



