430 .1. (IIIAIIAM KKHU. 



out to form a prominent knob ou each side, and the cercliral 

 heznisphere has become more distinct. 



From Stage 30 to 32 (figs. TO c, d, and k) the chief changes 

 consist in tlic close approximation of tlic iiifnndibnhir region 

 to the flooi' of the liind brain, in tlie appearance of tlie ])ineal 

 outgrowtli, and in the commencing forward growth of tht; 

 two hemisplieres. It is to be noted tluit up to nearly Stage 

 32 there is no obvious separation of mid-brain from thalamen- 

 cephalon. In a brain of about Stage 35 (fig. 10 r) the chief 

 advance consists in the considerable growth forwards of the 

 hind brain on each side, so as in side view to completely hide 

 the floor of the mid-brain. I'he roof of the thalamencephalon, 

 forming for the most part the ])ineal cushion,^ is now quite 

 sharply marked oif from the roof of the mid-brain. From 

 now onwards to Stage 38 changes in external conformation 

 are but slight, as will be seen from fig. lO g, the chief one 

 being in the upward growth of the hemisphere-roof, so that 

 it, with the pineal cushion, rises to about the same hori/.ontal 

 line as the summit of the mesencephalon. 



In the last stage (Stage 39), which I figure (fig. 10 h), a 

 marked advance towards the adult condition is seen, the 

 cerebral hemispheres having undergone a'^large increase 

 in antero-posterior length. The olfactory lobe is already 

 marked off. 



The chief change subse(pumt to this consists in the furflu'r 

 great elongation of the brain axis. 



Dorsal Aspect of t\\v Brain. 



'I'he earliest stage which I have figured (fig. 8 a. Stage 31) 

 illustrates (1) the relatively enormous size of the hind bi-ain ; 

 (2) the fact that mesencephalon and thalamencephalon form 

 a single perfectly definite brain region, on the roof of which 

 the pineal body has appeared ; and (•">) the i)aired independent 

 rudiments of the hemispheres. 



In the view of Stage 35 (PI. 2(i, fig. . 8 1-,) the forward 

 ' Zi rl)cl polst cr. 



