30 Mr. Home’s Additions, &c. 
each brain was invested, in the usual way, by its own proper 
coverings ; but the dura mater which covered the cerebrum of 
the upper brain, adhered firmly to the dura mater of the lower 
brain : the two brains were therefore separate and distinct, 
having a complete partition between them, formed by an union 
of the durae matres. 
When the contents of the double skull were taken out, and 
this union of the durae matres more particularly examined, a 
number of large arteries and veins were seen passing through 
it, making a free communication between the blood vessels of 
the two brains. This is a fact of considerable importance, as it 
explains the mode in which the upper brain received its nou- 
rishment. 
Before these observations were communicated by Mr. Dent, 
it was natural to suppose that the two brains had been united 
into one mass ; as it was difficult to imagine in what way the 
upper brain could be supplied with blood. 
