Anatomy. — "The ontogenetic (ievelopnient of the Coi-jmx striatitin 

 in birds and a comparison with inamma/s and man". By 

 Dr. C. U. Ariëns Kappkrs. 



(Communicated at the meeting of November 25, 1922). 



In the last ten years the corpus striatum has been a centre of 

 interest as well for anatomists as pathologists, the latter chiefly 

 after the researches of Kinnier Wilson. 



There are however great differences in the intraventricular growths 

 to which this name is given in different vertebrates. 



Though I shall deal here chiefl3' with the corpus striatum in birds, 

 mammals and man, I will start with making some introductory 

 I'emarks on the intraventricular- grovvtiis in fishes since the same 

 p'rinciple which we shall meet in the amniota is already observed 

 here: viz. the fact that the so called striatal parts do not only arise 

 from the base of the forebrain init also from the mantle. 



If one looks at the forebruiu of a teleosl or ganoid, it seems as 

 if only the basal part of the forebrain consisted of nervous tissue, 

 whereas the dorsal part merely consists of a choroid membrane. 



Tliis however is only seemingly so. 



As a matter of fact, the two primordia generally observed in 

 forebrains, the basal one and the dorsal one (from the latter of 

 which (he mantle arises), are both present also in embryo's of 

 Teleosls and Ganoids. 



Whereas however the dorsal part in other fishes enlarges in a 

 manlle-like way, increasing chiefly in surface and folding inwaid, 

 the mantle primordium in Teleosts developes in a quite different 

 way. Instead of increasing in surface it increases in thickness, 

 thus narrowing the ventricle of the forebrain in which it protrudes. 



This increase in thickness even goes so far that the pallial part 

 bulges outward, pushing the dorsal wall latero-ventrally, in conse- 

 quence of which the roof membrane is stretched and widely extended 

 from left to right. 



Thus an everted pallium is formed in these fishes, in contrarj' 

 to the inverted mantle of other anifnals. 



This process of development is seen in all larvae of Teleosts, and 

 clearly demonstrated by a study of Lepidosteus osseus (a bony ganoid) 



