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Foramen magnum

Foramen magnum
File:Crane4 Foramen magnum.png
Upper surface of base of the skull. The hole indicated by an arrow is the foramen magnum
Occipital bone. Inner surface.
Latin Foramen magnum
Gray's p.129
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Anatomical terms of bone

The foramen magnum (Latin: great hole) is a large opening in the occipital bone of the human skull. It is one of the several oval or circular openings in the base of the skull (called foramina). The spinal cord, an extension of the medulla, passes through the foramen magnum as it exits the skull vault. Apart from the transmission of the medulla oblongata and its membranes, the foramen magnum transmits the vertebral arteries, the anterior and posterior spinal arteries, the tectorial membranes and alar ligaments. It also transmits the spinal component of the accessory nerve into the skull.

The foramen magnum is a very important feature in bipedal mammals. One of the attributes of a bipedal animal’s foramen magnum is a forward shift of the anterior border; this is caused by the shortening of the cranial base. Studies on the foramen magnum position have shown a connection to the functional influences of both posture and locomotion. The forward shift of the foramen magnum is apparent in bipedal hominins, including modern humans, Australopithecus africanus, and Paranthropus boisei. This common feature of bipedal hominins is the driving argument used by Michel Brunet that Sahelanthropus tchadensis was also bipedal, and may be the earliest known bipedal ape. The discovery of this feature has given scientists another form of identifying bipedal mammals. [1]

Other animals

In humans, the foramen magnum is farther underneath the head than in the other great apes. Thus, in humans, the neck muscles (including the occipitofrontalis muscle) do not need to be as robust in order to hold the head upright. Comparisons of the position of the foramen magnum in early hominid species are useful to determine how comfortable a particular species was when walking on two limbs (bipedalism) rather than four (quadrupedalism).

Additional images

Skull seen from below. The hole through which the medulla (shown in red) is passing is foramen magnum. 
Occipital bone. Foramen magnum shown in red. 
Human brain with dura mater intact. The foramen magnum is visible as the large hole in the centre. 

See also


This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

  1. ^ Russo, Gabrielle A.; Kirk, Christopher E. (November 2013). "Foramen magnum position in bipedal mammals". Journal of Human Evolution 65 (5): 656–670. doi:10.1016/j.jhevol.2013.07.007. Retrieved 12 March 2015. 

External links