Which bone joins all the bones of the cranium together?

The sphenoid bone is often referred to as the "keystone" of the cranial floor because it plays a crucial role in connecting all the other bones of the cranium together. Its unique butterfly shape and position at the base of the skull allow it to articulate with several other bones, including the frontal, parietal, temporal, and occipital bones, among others. This connectivity provides structural integrity to the cranial vault, making the sphenoid bone essential for maintaining the overall shape and function of the skull.

In contrast, the other bones specifically mentioned do not have the same extensive connections with all the cranial bones. The frontal bone, for example, primarily articulates with the parietal and nasal bones but does not connect to every other cranial bone. The temporal bone and occipital bone similarly have specific neighboring bones they connect with but do not serve as the central linking structure for the entire cranial assembly. The sphenoid’s position and its articulations establish it as the most significant bone for joining the bones of the cranium, which is why it is the correct answer.