Why Android SDK has no communication with Middleware Libraries?

While learning about android development by reading I couldn't get why there is no arrow between SDK and Middleware Libraries as shown in the image.Could anyone tell me then why Middleware Libraries are included in the image.

It says in Android in Practice that:the middleware includes libraries for many functions (data storage,graphics rendering, web browsing, and so on) and it also contains a special sub-section called the Dalvik runtime.

But I couldn't get why there is no communication between SDK and these(Middleware) libraries because I think Dalvik runtime should be definitely connected to the SDK.I got the image from Scribd.Could anyone help me.