546 



TEXT-BOOK OF EMBRYOLOGY 



the two halves of the pallial expansion (Fig. 47 1 ; bc )'> 0) the boundary line or 

 line of union with the thalamus lying caudally (pallio-thalamic boundary) 

 (Fig. 471, cd); (3) the boundary between pallium and corpus striatum (strio- 

 pallial boundary) (Fig. 47 1 , bd) . The boundaries of the future corpus striatum 

 are (1) the median (Fig. 471, ab), (2) the strio-pallial (Fig. 471, bd), (3) the 

 strio-thalamic or peduncular (Fig. 471, de) and (4) the strio-hypothalamic (Fig. 

 471, ae). The internal prominence which is the rudiment of the corpus 

 striatum, has three limbs or crura, (1) a ridge proceeding forward (anterior 

 crus), which corresponds externally to the furrow (external rhinal furrow) 

 forming the lateral boundary of the anterior olfactory lobe, (2) a middle crus 



Prosencephalon 

 (Fore ■ brain,' 



Corpora quaclrigeniioa 



Peduuculua cerebri 



Brachtum conjunotivnm 



and velum medullare 



auterius 



Rhincncephalon^- 

 Corpus striatum 



Para optica hypothalami ■ 



Pars uiamillaria hypothalami 



Pons [Varolii 



Para ventratls 

 Sulcus limitans 



Fig. 471. — From a model of the brain of a human embryo at the end of the first month, right 

 half, seen from the left. His, Spalteholz. 



corresponding to the constriction separating the two olfactory lobes, and (3) a 

 posterior crus corresponding to the posterior boundary of the posterior olfactory 

 lobe. This latter is merged with the earlier furrow separating the telencephalon 

 from the thalamus and hypothalamus (peduncular furrow). What may be 

 called the main body of the corpus striatum, from which these limbs radiate, 

 soon becomes expressed externally by a shallow depression in the lateral sur- 

 face of the hemispheres immediately dorsal to the olfactory lobes. This 

 depression is the first indication of the fossa Sylvii (Fig." 465). 



The boundaries of the pallial hemisphere above indicated are identical 

 with the boundaries of the future foramen of Monro. 



The median lamina uniting the two halves of the pallium and the two corpora 

 striata may be termed the lamina terminalis and represents the roof plate and 

 floor plate of this region. The point of meeting of the roof plate and floor 



