Final answer:
The 'walling off' of the orbit posteriorly is a term used to describe the bony partition that encloses the orbit, forming a cup-shaped cavity which houses and protects the eyeball and its associated muscles.
Step-by-step explanation:
The 'walling off' of the orbit posteriorly refers to the formation of a bony partition that results in the orbit appearing as a cup-shaped structure. This structure serves to house the eyeball and includes the muscles that are responsible for eye movements and lifting the upper eyelid. The walls of the orbit are composed of contributions from seven different skull bones: the frontal bone forms the roof, the zygomatic bone contributes to the lateral wall and floor, the maxilla primarily forms the medial floor with some contribution from the palatine bone, the ethmoid and lacrimal bones form much of the medial wall while the sphenoid bone forms the posterior orbit. This complex arrangement ensures that the orbit is safely partitioned from the cranial cavity, thus protecting the sensitive structures within the eye.