Expanded Extended Griewank's plus Rosenbrock's Function (F8F2)

In Matlab code of Expanded Extended Griewank's plus Rosenbrock's Function (F8F2), I am stuck at the following lines of code:

for i=1:(D-1)

fit=fit+F8F2(x(:,[i,i+1])); % what does concatenation in x(:,[i,i+1]) does?

end

fit=fit+F8F2(x(:,[D,1]));

function f=F8F2(x)

f2=100.*(x(:,1).^2-x(:,2)).^2+(1-x(:,1)).^2;

f=1+f2.^2./4000-cos(f2);

How does this code work to accomplish F8(F2(x1, x2)) + F8(F2(x2, x3)) + ... + F8(F2(xD-1, xD)) + F8(F2(xD, x1))?