The entepicondylar foramen is an opening in the distal (far) end of the humerus

Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

 (upper arm bone) present in some mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s. It is often present in primitive placentals, such as the enigmatic Madagascan Plesiorycteropus

Plesiorycteropus

Plesiorycteropus, also known as the bibymalagasy or Malagasy aardvark, is a recently extinct eutherian mammalian genus from Madagascar. Upon its description in 1895, it was classified with the aardvark, but recent studies have found little evidence to link it to aardvarks or any other order of...

. In most Neotominae

Neotominae

Neotominae is a subfamily of the family Cricetidae. It consists of four tribes, 16 genera, and many species of New World rats and mice, predominantly found in North America. Among them are the well-known deer mice, white-footed mice, packrats, and grasshopper mice.Neotomines are related to the...

 and all Tylomyinae

Tylomyinae

The subfamily Tylomyinae consists of several species of New World rats and mice including the vesper and climbing rats. They are not as well known as their relatives in the subfamilies Sigmodontinae and Neotominae...

 among cricetid

Cricetidae

The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...

 rodents, it is located above the medial epicondyle of the humerus

Medial epicondyle of the humerus

The medial epicondyle of the humerus, larger and more prominent than the lateral epicondyle, is directed a little backward. In birds, where the arm is somewhat rotated compared to other tetrapods, it is called ventral epicondyle of the humerus....

, but it is absent in all Sigmodontinae

Sigmodontinae

The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...

 and Arvicolinae

Arvicolinae

The Arvicolinae are a subfamily of rodents that includes the voles, lemmings, and muskrats. They are most closely related to the other subfamilies in the Cricetidae . Some authorities place the subfamily Arvicolinae in the family Muridae along with all other members of the superfamily Muroidea...

 and this trait has been suggested as a synapomorphy

Synapomorphy

In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

for the former subfamily.

Literature cited

• MacPhee, R.D.E. 1994. Morphology, adaptations, and relationships of Plesiorycteropus, and a diagnosis of a new order of eutherian mammals. Bulletin of the American Museum of Natural History 220:1–214.
• Weksler, M. 2006. Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data. Bulletin of the American Museum of Natural History 296:1–149.