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. 2016 Mar;299(3):385-99.
doi: 10.1002/ar.23309. Epub 2016 Jan 30.

Anatomy of Mole External Genitalia: Setting the Record Straight

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Free PMC article

Anatomy of Mole External Genitalia: Setting the Record Straight

Adriane Watkins Sinclair et al. Anat Rec (Hoboken). .
Free PMC article

Abstract

Anatomy of male and female external genitalia of adult mice (Mus musculus) and broad-footed moles (Scapanus latimanus) was re-examined to provide more meaningful anatomical terminology. In the past the perineal appendage of male broad-footed moles has been called the penis, while the female perineal appendage has been given several terms (e.g. clitoris, penile clitoris, peniform clitoris and others). Histological examination demonstrates that perineal appendages of male and female broad-footed moles are the prepuce, which in both sexes are covered externally with a hair-bearing epidermis and lacks erectile bodies. The inner preputial epithelium is non-hair-bearing and defines the preputial space in both sexes. The penis of broad-footed moles lies deep within the preputial space, is an "internal organ" in the resting state and contains the penile urethra, os penis, and erectile bodies. The clitoris of broad-footed moles is defined by a U-shaped clitoral epithelial lamina. Residing within clitoral stroma encompassed by the clitoral epithelial lamina is the corpus cavernosum, blood-filled spaces and the urethra. External genitalia of male and female mice are anatomically similar to that of broad-footed moles with the exception that in female mice the clitoris contains a small os clitoridis and lacks defined erectile bodies, while male mice have an os penis and a prominent distal cartilaginous structure within the male urogenital mating protuberance (MUMP). Clitori of female broad-footed moles lack an os clitoridis but contain defined erectile bodies, while male moles have an os penis similar to the mouse but lack the distal cartilaginous structure.

Keywords: clitoris; mice; moles; penis; prepuce; preputial space.

Figures

Figure 1
Figure 1
Side views of male and female broad-footed mole (A-C) and mouse (D & E) external genitalia. (F) External genitalia of the breeding season female broad-footed mole shown in (C), but at a ¾ side view showing the vaginal opening with forceps inserted. For both species the size of male and female external genitalia are remarkably similar. Red arrows in each panel denote the approximate level from which transverse sections in figure 2 were taken. For all images the cranial aspect is to the left.
Figure 2
Figure 2
Transverse sections of the external genitalia of male and female mouse (A & B) and broad-footed mole (C & D). See red arrows in figure 1 for the approximate level from which the sections were taken. The male and female perineal appendages illustrated grossly (Fig. 1) and in transverse sections (2A-D) are indicative of the prepuce by virtue of having the following features: (a) an absence of erectile bodies, (b) covered externally by a hair-bearing epidermis, (c) lined by a non-hair-bearing inner epithelium defining the preputial space, which in the case of males (B & D) houses the penis. Double-headed arrows denote hair follicles. Preputial gland ducts present in mice are labeled PPGD.
Figure 3
Figure 3
Mid-sagittal section of the mouse penis (A) and a three dimensional reconstruction of the broad-footed mole external genitalia (B) and associated preputial space. Much of the mouse prepuce has been removed (A), but the fact that the mouse penis is housed within the preputial space is clearly evident. Note the continuity of the inner preputial epithelium with penile surface epithelium denoted by the large black arrows. (B) The three dimensional reconstruction of the broad-footed mole external genitalia, which also indicates that the penis is an “internal organ” housed within the preputial space. The large opposed white arrows in (B) indicate the junction between the external part of the penis that resides within the preputial space and the internal part of the penis that lies deep to the preputial space. In (B) red denotes the os penis, green denotes the urethra, orange denotes the penis, yellow denotes the corpus cavernosum, purple denotes prepuce and preputial space.
Figure 4
Figure 4
Transverse sections of the clitoris of the mouse (A) and broad-footed mole (C) and the penis of the mouse (B) and broad-footed mole (D). The clitoris of both species is defined by a U-shaped clitoral epithelial lamina (A & C). The boundaries of clitoral stroma are defined by the clitoral epithelial lamina as well as the green dotted lines. In both species the female urethra is located partially within and partially outside of clitoral stroma. The extent of retention of the urethra within clitoral stroma is dependent upon the proximal/distal position of the section. In more proximal regions the urethra is completely ventral to clitoral stroma, which is the case for both mice and moles. Note the absence of defined erectile bodies within the mouse clitoris (A), and the presence of a corpus cavernosum (CC) located within the clitoral stroma of the broad-footed mole (C). The mouse and broad-footed mole penis is round to oval in shape, contains a urethra, and erectile bodies (double-headed arrows in [B] denote the corpus cavernosum glandis). The corpora cavernosa urethrae (CCUr) is highlighted by a dotted line. Note the network of blood filled cavernous spaces within the penis of the broad-footed mole (D). An os penis is present in both species.
Figure 5
Figure 5
Diagrams demonstrating that the penis is an “internal” organ housed within the preputial space. (A) Side view of the adult mouse external prepuce with a colorized SEM image superimposed. The penis is in its typical position almost 2mm from the tip of the prepuce. (B) Drawing of the mouse external genitalia depicting the external prepuce. (C) Three dimensional reconstruction of the prepuce and penis of an adult broad-footed mole demonstrating the position of penis relative to the prepuce. As in the mouse, the mole penis at rest is an “internal” organ housed within the preputial space. The perineal appendage (prepuce) merges with the body surface (green asterisks). The red arrowheads denote the reflection of the inner preputial epithelium onto the surface of the penis. Note the morphometric measures mentioned in the text.
Figure 6
Figure 6
Dissected prepuce and penis of the mouse. The two large opposed black arrows denote the junction between the external portion of the penis (glans) housed within the preputial space (as signified by the dotted lines) and the internal body of the penis lying deep to the preputial space. The position of the glans is illustrated.
Figure 7
Figure 7
Images demonstrating the “internal” position of the mouse (A) and broad-footed mole clitoris (E) as well as the changing position of the urethra in both species on a proximal/distal basis (B-D and F-H). In (A) a three dimensional reconstruction of the U-shaped clitoral lamina (blue) is superimposed on a side view of adult female mouse external genitalia. Sections B-D in proximal to distal order illustrate the changing position of the urethra relative to the clitoral lamina. Note also that sections (B & C) contain a stand-alone urethra. In (D) a complex epithelium is present in which the clitoral lamina and urethra are fused together. In (E), a three dimensional reconstruction of the broad-footed mole clitoris, the internal position of the clitoris in evident along with its color-coded internal constituents. In sections (F-H), taken at the positions so indicated, the stand-alone urethra is seen (F) as well as the preputial space (G) where the epithelium of the clitoral lamina and urethra are fused. (H) is a section through the female prepuce only showing the preputial groove. CC=corpus cavernosum.
Figure 8
Figure 8
Transverse sections through the penis (A) and clitoris (B) of an adult broad-footed mole. In (A) note that the penis (P) resides within the preputial space (PS) and contains the urethra (U), the corpus cavernosa (CC) surrounded by the tunica albuginea (T), and blood-filled spaces (BV). The os penis is not present at the level of this section. In (B) the U-shaped clitoral lamina partially surrounds the urethra (U). Residing within the space defined by the clitoral lamina is the corpus cavernosa (CC) surrounded by the tunica albuginea (T) and blood filled spaces (BV). Note that clitoral stroma (CS) within the U-shaped clitoral lamina is in continuity ventrally with the surrounding stroma (double-headed arrows). Finally, the substance of the preputial wall contains hair follicles (H) in both (A) and (B).
Figure 9
Figure 9
Drawings of the external genitalia of male and female rat, mouse, human and mole (Scapanus latimanus). The upper row depicts penises of the three species. The lower row contains mole (Scapanus latimanus) male and female drawings that are to morphometric scale as per the Results text. The mouse and the rat have two prepuces: (a) an external protective prepuce, which creates a voluminous space housing the penis and (b) an internal prepuce integral to the penis itself, which is similar to that of humans. The external prepuce creates the perineal appendage seen externally in both rats, mice and Scapanus latimanus. The arrangement of structures for Scapanus latimanus is similar to that of the mouse and rat with the exception of the absence of an internal prepuce. Note that in Scapanus latimanus the prepuce is non-integral to both the penis and clitoris.

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