Trying to understand skinned mesh shader

I was trying to understand how skinned mesh shader works and I see that if its type of skinned mesh it uses bindMatrix, bindMatrixInverse, boneMatrices, skinIndex and skinWeight as uniform

but when I checked the skinned mesh (which i am using in my scene) shader’s info using onBeforeCompile to see what its sending to shader, I don’t see any of that uniform being sent to the shader and skinned mesh is working fine. So how shader is receiving those uniforms?

You can see in img below all the uniforms which are being sent to the shader and none of the above mentioned uniforms which are required for skinned mesh are present here which is weird

can somebody please explain to me whats happening?