Animal clitoris

The clitoris ( or ; : clitorises or clitorides) is a female sex organ present in mammals, ostriches and other amniotes.

Although the clitoris exists in all mammal species, most studies deal with the human clitoris - few detailed studies of the anatomy of the clitoris in non-humans exist. The clitoris is especially developed in fossas, apes, lemurs, moles, and, like the penis in many non-human placental mammals, often contains a small bone. In females, this bone is known as the os clitoridis. The clitoris exists in turtles, ratites, crocodiles, and in species of birds in which the male counterpart has a penis. The hemiclitoris is one-half of a paired structure in lizards and snakes. Some intersex female bears mate and give birth through the tip of the clitoris; these species are grizzly bears, brown bears, American black bears and polar bears. Although the bears have been described as having "a birth canal that runs through the clitoris rather than forming a separate vagina" (a feature that is estimated to make up 10 to 20 percent of the bears' population), scientists state that female spotted hyenas are the only non-intersex female mammals devoid of an external vaginal opening, and whose sexual anatomy is distinct from usual intersex cases.

Moles
Many species of talpid moles exhibit peniform clitorises that are tunneled by the urethra and are found to have erectile tissue, most notably species from the Talpa genus found in Europe. Unique to this clade are the presence of ovotestes, wherein the female ovary also is mostly made up of sterile testicular tissue that secretes testosterone with only a small portion of the gonad containing ovarian tissue. Genetic studies have revealed that females of these species have an XX genotype and do not have any translocated Y-linked genes. Detailed developmental studies of Talpa occidentalis have revealed that the female gonads develop in a "testis-like pattern". DMRT1, a gene that regulates development of Sertoli cells, was found to be expressed in female germ cells before meiosis, however no Sertoli cells were present in the fully-developed ovotestes. Additionally, the female germ cells only enter meiosis postnatally, a phenomenon that has not been found in any other eutherian mammal. Phylogenetic analyses have suggested that, like in lemuroids, this trait must have evolved in a common ancestor of the clade, and has been "turned off and on" in different talpid lineages.

Female European moles are highly territorial and will not allow males in to their territory outside of breeding season, the probable cause of this behavior being the high levels of testosterone secreted by the female ovotestes. During the non-breeding season, their vaginal opening is covered by skin, akin to the condition seen in mouse and dwarf lemurs.

Domestic cats
Researchers studying the peripheral and central afferent pathways from the feline clitoris concluded that "afferent neurons projecting to the clitoris of the cat were identified by WGA-HRP tracing in the S1 and S2 dorsal root ganglia. An average of 433 cells were identified on each side of the animal. 85 percent and 15 percent of the labeled cells were located in the S1 and S2 dorsal root ganglia, respectively. The average cross sectional area of clitoral afferent neuron profiles was 1.479±627 μm2." They also stated that light "constant pressure on the clitoris produced an initial burst of single unit firing (maximum frequencies 170–255 Hz) followed by rapid adaptation and a sustained firing (maximum 40 Hz), which was maintained during the stimulation" and that further examination of tonic firing "indicate that the clitoris is innervated by mechano-sensitive myelinated afferent fibers in the pudental nerve which project centrally to the region of the dorsal commissure in the L7-S1 spinal cord".

Sheep
The external phenotype and reproductive behavior of 21 freemartin sheep and two male pseudo-intersex sheep were recorded with the aim of identifying any characteristics that could predict a failure to breed. The vagina's length and the size and shape of the vulva and its clitoris were among the aspects analyzed. While the study reported that "a number of physical and behavioural abnormalities were detected," it also concluded that "the only consistent finding in all 23 animals was a short vagina which varied in length from 3.1 to 7.0 cm, compared with 10 to 14 cm in normal animals."

Mice
In a study concerning the clitoral structure of mice, the mouse perineal urethra was documented as being surrounded by erectile tissue forming the bulbs of the clitoris. The researchers stated, "In the mouse, as in human females, tissue organization in the corpora cavernosa of the clitoris is essentially similar to that of the penis except for the absence of a subalbugineal layer interposed between the tunica albuginea and the erectile tissue."