Final answer:
Specialized veins in the heart and brain that lack vasomotion are known as intracranial sinuses, which are crucial for venous drainage in the brain.
Step-by-step explanation:
Specialized veins in the heart and brain that do not possess the capability for vasomotion are called intracranial sinuses. These structures are part of the venous drainage system of the brain, comprising various sinuses such as the superior and inferior sagittal sinuses, straight sinus, cavernous sinuses, the petrosal sinuses, and the occipital sinuses. Unlike other veins and vessels in the body, these sinuses cannot contract or relax to regulate blood flow, which is what is meant by the absence of vasomotion.