What determines the vector length that BCFUN should returns?

What determines the vector length that BCFUN should returns? Because i have this error in my code:

Error in calling BVP4C(ODEFUN,BCFUN,SOLINIT,P1,P2...): The boundary condition function BCFUN should return a column vector of length 2.

In the problem that i have to solve i need to satisfice 4 boundary conditions in a system of two equations. But matlab only allows me to have two. This is my code :

Main:

          init=bvpinit(linspace(-10,0,10),@initEq5_7_);
          sol=bvp4c(@rhsEq5_7,@bcEq5_7,init,[],c);
          z=linspace(-10,0,100);
          p=deval(sol,z);

        hold on;
        plot(z,p(1,:),'r--');
        plot(z,p(2,:),'b');

---------------------
function v = initEq5_7_(x)
v = [ sin(x)
      sin(x)];

-------------------------
function rhs=rhsEq5_7(x,y,c)
s=2;
mu=2;
k=1;
alpha=-(mu/(c^2-s^2));
beta=2*k/s;
rhs=[-alpha*y(1)*(c-s*(2*y(2)-1)) 
     -beta*y(1)*(1-y(2))*y(2)];

---------------------------
function rhs=bcEq5_7(l,r,c)
ql=0.5;
qr=0.01;
rhs=[l(1)
     r(1)
     l(2)  
     r(2)
        ];

It doesn't make sense to me, because i have seen code with more boundary conditions than equations. Thanks in advance.