NERVOUS SYSTEM OF THE VERTEBRATA. 



441 



striatum loses its primitive relations to the descending cornu. 

 The reduction in size of the foramen of Munro above mentioned 

 is, to a large extent, caused by the growth of the corpora striata. 

 The corpora striata are united at their posterior border with 

 the optic thalami. In the later stages of development the area 

 of contact between these two pairs of ganglia increases to an 

 immense extent (fig. 261), and the boundary between them 

 becomes somewhat obscure, so that the sharp distinction which 

 exists in the embryo between the thalamencephalon and cerebral 

 hemispheres becomes lost. This change is usually (Mihalkovics, 



EIG. 260. TRANSVERSE SECTION THROUGH THE BRAIN OF A SHEEP'S EMBRYO 



OF 27 CM. IN LENGTH. (From Kolliker.) 

 The section passes through the level of the foramen of Munro. 

 st. corpus striatum ; in. foramen of Munro ; t. third ventricle ; pi. choroid plexus 

 of lateral ventricle; / falx cerebri; th. anterior part of optic thalamus; ch. optic 

 chiasma; o. optic nerve; c. fibres of the cerebral peduncles; h. cornu ammonis; 

 /. pharynx ; sa. pre-sphenoid bone ; a. orbito-sphenoid bone ; s. points to part of the 

 roof of the brain at the junction between the roof of the third ventricle and the lamina 

 terminalis ; /. lateral ventricle. 



Kolliker) attributed to a fusion between the corpora striata and 

 optic thalami, but it has recently been attributed by Schwalbe 

 (No. 849), with more probability, to a growth of the original 

 surface of contact, and an accompanying change in the relations 

 of the parts. 



