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The Function of the Entepicondylar Foramen in Mammals

Stuart O. Landry, Jr.
The American Midland Naturalist
Vol. 60, No. 1 (Jul., 1958), pp. 100-112
DOI: 10.2307/2422468
Stable URL: http://www.jstor.org/stable/2422468
Page Count: 13
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The Function of the Entepicondylar Foramen in Mammals
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Abstract

The entepicondylar foramen or supracondyloid foramen is a canal through the distal end of the humerus of mammals for the passage of the median nerve and brachial artery. Neither the function of this structure, where it exists, nor the reason for its disappearance, where it does not exist, have ever been satisfactorily explained. Theories of the function of the entepicondylar foramen may be divided into. three types: (1) theories proposing that the foramen protects the traversing structures; (2) theories proposing that the presence or absence of the foramen depends upon the shape of the distal end of the humerus; and (3) ,theories proposing that the bony arch of the foramen acts as a brace or strut. This paper rejects all of these theories and proposes that the entepicondylar foramen in quadrupeds acts as a retinaculum for the median nerve, to prevent it from slumping across the angle of the elbow. In quadrupeds, the axilla is deep, enclosing most of the humerus, so that the skin over the elbow is loose and does not hold down the nerve. The median nerve is the only filiform structure of the arm requiring this retention. The vessels give off numerous branches, while the radial and ulnar nerves pass behind .the humerus before entering the forearm. Cursorial and ungulate mammals have lost the entepicondylar foramen because they do not abduct the humerus and thus do not expose the median nerve. Anthropoid primates (including man) have lost the foramen because .their humeri have become highly abductible. The axilla has become greatly shortened and the skin fits tightly over the elbow, effectively restraining the median nerve.

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