In the sphenoid bone

Sphenoid bone

The sphenoid bone is an unpaired bone situated at the base of the skull in front of the temporal bone and basilar part of the occipital bone.The sphenoid bone is one of the seven bones that articulate to form the orbit...

, the posterior border, smooth and rounded, is received into the lateral fissure of the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

; the medial end of this border forms the anterior clinoid process, which gives attachment to the tentorium cerebelli

Tentorium cerebelli

The tentorium cerebelli or cerebellar tentorium is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.-Anatomy:...

; it is sometimes joined to the middle clinoid process

Middle clinoid process

The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes.-Etymology:...

 by a spicule of bone, and when this occurs the termination of the groove for the internal carotid artery

Internal carotid artery

In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....

 is converted into a foramen

Foramen

In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...

(carotico-clinoid).

Etymology

Clinoid likely comes from the Greek root klinein or the Latin clinare, both meaning "sloped" as in "inclined."