During anatomy class, the professor pointed out the bullae on the skull model to explain their structure.

bullae 是名词 bulla 的复数形式，bulla 来自拉丁语，意思是"气泡、泡状物"，在解剖学中特指骨骼表面鼓起的泡状结构，如颅骨上的"鼓泡"。