168 



COMPARATIVE ANATOMY 



The hemispheres are more highly developed, and the cortex is 

 definitely differentiated and contains the characteristic pyramidal 

 cells. In many cases also a distinct hippocampal lobe (Figs. 139, 140) 



1 Lol 



Co,pMH N Illl NH 



Fis. 138. LONGITUDINAL SECTION THROUGH THE BRAIN OF A, Rana, AND B, 

 Hatteria. (A after H. F. Osborn.) 



VH, MH, HH, NH, prosen-, mesen-, meten-, and myelencephalon ; H in (B), 

 hemisphere, which possesses a furrow on its median face, where it is perforated 

 by numerous vascular foramina (S) : this furrow forms the boundary between 

 the hemisphere and olfactory tract, the main root of which is seen at f ; Lol; 

 olfactory lobe ; /, II, IV, origins of the olfactory, optic, and pathetic 

 nerves ; Ep, **, base of epiphysis, which is not shown ; Ch.opt and Ch, optic 

 chiasma ; Lt, lamina terminalis (the reference line should point to the cut 

 edge below Ba and*), Co.a,* anterior commissure ; Ca, Ba, corpus callosum ; 

 F.Mo, Mo, foramen of Monro, above which, in A, is seen the folded choroid 

 plexus ; Cos, superior commissure ; Co.p, posterior commissure ; V 1H and F /r , 

 third and fourth ventricles ; Th. opt and M, optic thalamas ; Lo (in B), aper- 

 ture, and Fu, furrow in the wall of the third ventricle ; Aq, Aq.Syl, aqueduct 

 of Sylvius ; Jnf, infundibulum ; Hyp, hypophysis. 



is present (Hatteria, Chelonia, Crocodilia), and the commissural 

 system between the hemispheres known as the fornix as well as a 

 so-called " corpus callosum " (comp. p. 174) are present in rudiment. 



