818 



on its lateral surface is very sinall. In tliis res|)ect tliis great surface 

 area wliicli is formed bj' the iijperstriatum is sharply ditlerentiated 

 from the pallium which receives a relatively rich supply of vessels 

 entering from the surface. The result of this arrangement is that 

 the blood supply of tiie lateral pait of the hyperstriatum is derived 

 from a series of vessels penetrating deeply into the hemisphere along 

 the line of the external medullary lamina and sending frequent 

 branches laterally. Such a deep penetration of vessels demands an 

 explanation which is to be sought on |ihy logeiietic grounds. The 

 explanation which suggests itself is that the hyperstriatal arteiy of 

 this avian brain represents the lateral striate artery of reptiles and 

 the liypopallial (claustral) artery of man. That, in effect it is a 

 greatly hypertrophied vessel originally in series with the pallial 

 arteries which are in the bird's brain mainly confined to the dorsal 

 aspect, the lateral series iiaving been greatly reduced in importance; 

 and further that this hyperlro|)hy has occurred because the hyper- 

 striatum is |iallial in origin. The hy|)erstriatum and the arciiistriatum 

 together re|)resent the hypopallium of reptiles and therefore also the 

 liypopallial elements of the corpus striatum (hyperstriatum) and of 

 the nucleus amygdalae (arciiistriatum) of the mammalian biain, (cf. 

 Ei,i,ioT Smith 1919a; Dart 1920). 



The mesostriatum can be excluded from this complex on account 

 of the difTleience iti the origin of its blood supply alone. For the 

 vessels situated more medially (paleostriatal arteries) supply not 

 only the basal nucleus or pdlaeostruituni priviitivum (Ahiëns Kappkrs 

 1922) but the extensive mesostriatum which surrounds it, (fig. 5). 

 If the criterion of blood supply is to be applied (cf. Shellshear op. 

 cit. i>. 35) in this case, the mesostriatum must be regarded as an 

 augmentative homology of the paleostriatum so forming ihepalaeo- 

 slriatum augmentatum of Akiens Kappers (1922). 



An examination of a series of sections of Pratincola rubra (figured 

 by Arikns Kappers in his text book, 1921) Casuaris, Athene noctua, 

 Paleornis, Ciconia alba, reveals the fact that the same vascular 

 arrangement as described in Aptenjx holds for Aves in general. 

 But in Apteri/x the arrangement is displayed with the greatest 

 clearness. 



It follows from the above discussion that the lamina medullaris 

 externa of birds is the line of separation of the neostriatum from 

 the palaeostriatum and that the point where this lamina reaches 

 the ventricle (e. g. fig. 6) represents the site of the jissin-a neo- 

 palaeostriatica. which is clearly seen if embryonic stages of the 

 chick's brain be studied, (cf. Arii^ins Kapp1';hs, 1922, p. 140). 



