450 
Dr Duckworth, Description of a 
both traced from sections of the hind-brain of the “control ” 
specimen, and in Fig. 13, the depression ( x ) is quite deep, although 
as is shewn by the appearance of the mid-brain, the section is not 
in the middle line, and certainly not so near it as that shewn in 
Fig. 14. But in the latter the depression is not clearly marked. 
In the classical works on the embryology of the brain, there is 
some obscurity on this point, which however is not sufficiently 
important in the present connexion, to deserve more than a 
passing reference. The depression or pit is very distinct in the 
human foetal brain figured in the Archiv fur Anatomie, 1892, 
Anatomischer Theil, Fig. 18, S. 401. 
In the monstrous pig, the arrest of brain development had 
occurred in front of the third cerebral vesicle in the position of 
the “isthmus,” and the second cerebral flexure had just made its 
effect felt. As is well known, this second flexure is dorsal in 
direction. It affects the region lying immediately in front of the 
pons varolii, though the latter structure is only partially affected 
by this influence. But just below this level the bueco-pharyngeal 
membrane is situated. In the present specimen, we have seen 
that the anatomical structures (viz. the central nervous system) 
on the dorsal aspect of the vertebral axis had been arrested in 
development at this level. And when attention is transferred to 
the structures on the ventral aspect, it will be seen that their 
growth also had been arrested quite definitely, and that the 
bucco-pharyngeal membrane had never been perforated. 
Fig. 15. 
Fig. 16. 
Before terminating this account of the central nervous system, 
it is however interesting to refer briefly to the state of the spinal 
cord. Transverse sections of this structure were made in the 
cervical region (Fig. 15), and were found to differ in no particular 
from the control sections (Fig. 16). It is especially important to 
