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Theos clitoridis (also called theos clitoris,clitoral bone orbaubellum;pl.:baubella) is a bone inside theclitoris of manyplacental mammals. It is absent from the human clitoris, but present inthe clitoris of some primates, such asring-tailed lemurs and non-humangreat apes. However, in the latter case, the bone is greatly reduced in size.[1][2][3] It is homologous to thebaculum in male mammals.
The structure is more evolutionarily labile than the baculum, exhibiting both more inherent variability and more gains and losses over time,[4] which has been interpreted as evidence for its non-functionality.[4]
Other work posits that the variation in the os clitoridis could be driven by intersexual conflict, lock-and-key genital evolution, andcryptic female choice, especially given the high level of variation within species as well as between them.[5]
The os clitoridis was described in 1666 byClaude Perrault inotters and in thelioness.[6]
The termos clitoridis was used in 1819 byFriedrich Sigismund Leuckart regarding thecapuchin monkey.[7]
This bone was namedbaubellum byGuy Chester Shortridge in 1934,[8] but it is much less common in comparison to the use of the wordbaculum. TheLatin termsos clitoris andos clitoridis are most often found in scientific publications.
The os clitoridis has been described in species belonging to theordersChiroptera,Primates,Rodentia andCarnivora.[9] As with thebaculum, this wide distribution suggests a primitive character that has been lost in somephylogenetic branches of the classMammalia.
Depending on the species, the presence of this bone varies from one specimen to another. It has been observed, for example, in only 30% ofAmerican red squirrels.[10] Its presence is even rarer indogs: 3% (6 out of 200) presence on a radiological sample ofAmerican Cocker Spaniels and 2% (4 out of 200) for theGerman Shorthaired Pointer.[11]
The shape and size vary greatly from one species to another. The size is often very small:[a]
The os clitoridis is often present, or even prominent, during the embryonic or immature phase, and then decreases with age. For example, in a walrus, the size of the bone tends to shrink as the years pass.[14]
The exact function of the os clitoridis is not known, but a function duringcopulation is assumed.[16] For some, the species distribution would be the same as the baculum.[15] The os clitoridis would be an equivalent, withoutevolutionary function, of the baculum, persisting or disappearing during sexual differentiation under hormonal influence. Experiments with treatment of thespleen withtestosterone, led to a persistence or increase in the size of the os clitoridis.[17]