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The penis bone, or baculum, is present in many orders of mammals, although its function is still relatively unknown, mainly due to the challenges with studying the baculum in vivo. Suggested functions include increasing vaginal friction, prolonging intromission and inducing ovulation. Since it is difficult to study baculum function directly, functional morphology can give important insights. Shape complexity techniques, in particular, are likely to offer a useful metric of baculum morphology, especially since finding homologous landmarks on such a structure is challenging. This study focuses on measuring baculum shape complexity in the Musteloidea-a large superfamily spanning a range of body sizes with well-developed, qualitatively diverse bacula. We compared two shape complexity metrics-alpha shapes and ariaDNE and conducted analyses over a range of six different coefficients, or bandwidths, in 32 species of Musteloidea. Overall, we found that shape complexity, especially at the baculum distal tip, is associated with intromission duration using both metrics. These complexities can include hooks, bifurcations and other additional projections. In addition, alpha shapes complexity was also associated with relative testes mass. These results suggest that post-copulatory mechanisms of sexual selection are probably driving the evolution of more complex-shaped bacula tips in Musteloidea and are likely to be especially involved in increasing intromission duration during copulation., (© 2023 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)

The crocodylian phallic glans is the distal inflatable structure that makes the most direct contact with the female cloacal and associated reproductive tract openings during copulation. Therefore, its form and function directly impact female tissue sensory interactions and insemination mechanics. Compared to mammals, less is known about glans functional anatomy among other amniotes, including crocodylians. Therefore, we paired an ex vivo inflation technique with magnetic resonance imaging 3D-reconstructions and corresponding histological analyses to better characterize the morphological glans restructuring occurring in the Nile crocodile (Crocodylus niloticus) at copulation. The expansion of contiguous inflatable spongiform glans tissues is variably constrained by adjacent regions of dense irregular collagen-rich tissues. Therefore, expansion shows regional differences with greater lateral inflation than dorsal and ventral. Furthermore, this enlargement elaborates the cup-like glans lumen, dorsally reorients the glans ridge, stiffens the blunt and bifid glans tip, and putatively works to seal the ventral sulcus spermaticus semen conduit groove. We suggest how these dynamic male structures may interact with structures of the female cloacal urodeum and how these morphological changes, in concert with the varying material properties of the structural tissue compartments visualized in this study, aid copulatory gamete transfer and resulting fecundity. RESEARCH HIGHLIGHTS: Nile crocodile glans inflation produces a reproductively relevant copulatory structure directing insemination and female tissue interactions. Pairing magnetic resonance imaging 3D reconstruction with corresponding histology effectively studies functional anatomy., (© 2020 Wiley Periodicals, Inc.)

The penises of bats are taxonomically distinctive in size and shape. In addition, they are variable in microscopic anatomy, indicating that histomorphological studies of copulatory organs of bats may help understanding their successful reproductive strategies. We studied adult males of 13 species of vespertilionid and phyllostomid bats. Both families exhibited the basic structure of the vascular penis of mammals: the hydrostatic elements of the corpora cavernosa and the corpus spongiosum surrounding the urethra, as well as accessory cavernous tissue. Variation in the position and amount of the tissues were observed in these families. Vespertilionid bats have a small glans penis with abundant accessory cavernous tissue on the prepuce and a highly variable baculum. The baculum varied in size and morphology, even among congeneric species, such as the three Lasiurus species and the two Myotis species. Phyllostomid species possess no bacula, but vascular structures are present to produce penile stiffening, particularly on the glans. Variation in the microscopic anatomy of the phyllostomid prepuce was observed, for example, Artibeus species had accessory cavernous tissue surrounded by a tunica albuginea, but Carollia perspicillata had two bundles of striated musculature and some adipose tissue; abundant pigments were present in the prepuce of most species., (© 2019 Wiley Periodicals, Inc.)

Complete diphallia, a rare urogenital congenital anomaly in which a male is born with two fully formed phalluses, occurs in one out of every five to six million live births. The condition is characterized by two separate phalluses, each of which comprise a pair of corpora cavernosa and one corpus spongiosum with an orthotopic urethra. Approximately 100 cases have been reported worldwide, and it is thought that each case is unique. This article discusses diphallia, urethral duplication, and bladder duplication and concludes with a case study involving a three-year-old male born to consanguineous parents from a small, remote community in Ecuador who underwent surgery for correction of a complete coronal penile and bladder duplication. After consultation, the patient was scheduled for a right penectomy and cystoplasty., (© AORN, Inc, 2019.)

Objective: This study measured anogenital distance (AGD) during late second/early third trimester of pregnancy to confirm previous findings that AGD can be measured noninvasively in the fetus using ultrasound and further showed differences in reference ranges between populations., Method: Two hundred ten singleton pregnancies were recruited at the Rosie Hospital, Cambridge, UK. A 2D ultrasound was performed between 26 and 30 weeks of pregnancy. AGD was measured from the centre of the anus to the base of the scrotum in males and to the posterior convergence of the fourchette in females., Results: A significant difference in AGD between males and females (P < .0001) was found, replicating previous results with a significant correlation between estimated fetal weight (EFW) and AGD in males only (P = .006). A comparison of AGD using reference data from an Israeli sample (n = 118) and our UK sample (n = 208) showed a significant difference (P < .0001) in both males and females, after controlling for gestational age (GA)., Conclusion: Our results confirm that AGD measurement in utero using ultrasound is feasible. In addition, there are strong sex differences, consistent with previous suggestions that AGD is influenced by prenatal androgen exposure. AGD lengths differ between the UK and Israel; therefore, population-specific normative values may be required for accurate clinical assessments., (© 2019 The Authors. Prenatal Diagnosis Published by John Wiley & Sons Ltd.)

The taxonomy of freshwater pulmonates (Hygrophila) has been in a fluid state warranting the search for new morphological criteria that may show congruence with molecular phylogenetic data. We examined the muscle arrangement in the penial complex (penis and penis sheath) of most major groups of freshwater pulmonates to explore to which extent the copulatory musculature can serve as a source of phylogenetic information for Hygrophila. The penises of Acroloxus lacustris (Acroloxidae), Radix auricularia (Lymnaeidae), and Physella acuta (Physidae) posses inner and outer layers of circular muscles and an intermediate layer of longitudinal muscles. The inner and outer muscle layers in the penis of Biomphalaria glabrata consist of circular muscles, but this species has two intermediate longitudinal layers separated by a lacunar space, which is crossed by radial and transverse fibers. The muscular wall of the penis of Planorbella duryi is composed of transverse and longitudinal fibers, with circular muscles as the outer layer. In Planorbidae, the penial musculature consists of inner and outer layers of longitudinal muscles and an intermediate layer of radial muscles. The penis sheath shows more variation in muscle patterns: its muscular wall has two layers in A. lacustris, P. acuta, and P. duryi, three layers in R. auricularia and Planorbinae and four layers in B. glabrata. To trace the evolution of the penial musculature, we mapped the muscle characters on a molecular phylogeny constructed from the concatenated 18S and mtCOI data set. The most convincing synapomorphies were found for Planorbinae (inner and outer penis layers of longitudinal muscles, three-layered wall of the penis sheath). A larger clade coinciding with Planorbidae is defined by the presence of radial muscles and two longitudinal layers in the penis. The comparative analysis of the penial musculature appears to be a promising tool in unraveling the phylogeny of Hygrophila., (© 2019 Wiley Periodicals, Inc.)

Background and Purpose: KCNQ-encoded voltage-dependent potassium channels (Kv 7) are involved in the regulation of vascular tone. In this study we evaluated the influence of Kv 7 channel activation on smooth muscle relaxation in rat penile arteries and corpus cavernosum from normal and spontaneously hypertensive, heart failure-prone (SHHF) rats - a rat model of human metabolic syndrome., Experimental Approach: Quantitative PCR and immunohistochemistry were used to determine the expression of KCNQ isoforms in penile tissue. Isometric tension was measured in intracavernous arterial rings and corpus cavernosum strips isolated from normal and SHHF rats., Key Results: Transcripts for KCNQ3, KCNQ4 and KCNQ5 were detected in penile arteries and corpus cavernosum. KCNQ1 was only found in corpus cavernosum. Immunofluorescence signals to Kv 7.4 and Kv 7.5 were found in penile arteries, penile veins and corpus cavernosum. The Kv 7.2-7.5 activators, ML213 and BMS204352, relaxed pre-contracted penile arteries and corpus cavernosum independently of nitric oxide synthase or endothelium-derived hyperpolarization. Relaxations to sildenafil, a PDE5 inhibitor, and sodium nitroprusside (SNP), an nitric oxide donor, were reduced by blocking Kv 7 channels with linopirdine in penile arteries and corpus cavernosum. In SHHF rat penile arteries and corpus cavernosum, relaxations to ML213 and BMS204352 were attenuated, and the blocking effect of linopirdine on sildenafil-induced and SNP-induced relaxations reduced. KCNQ3, KCNQ4 and KCNQ5 were down-regulated, and KCNQ1 was up-regulated in corpus cavernosum from SHHF rats. KCNQ1-5 transcripts remained unchanged in penile arteries from SHHF rats., Conclusions and Implications: These data suggest that Kv 7 channels play a role in erectile function and contribute to the pathophysiology of erectile dysfunction, an early indicator of cardiovascular disease., (© 2016 The British Pharmacological Society.)

Detailed knowledge of histomorphology is a prerequisite for the understanding of function, variation, and development. In bats, as in other mammals, penis and baculum morphology are important in species discrimination and phylogenetic studies. In this study, nondestructive 3D-microtomographic (microCT, µCT) images of bacula and iodine-stained penes of Pipistrellus pipistrellus were correlated with light microscopic images from undecalcified surface-stained ground sections of three of these penes of P. pipistrellus (1 juvenile). The results were then compared with µCT-images of bacula of P. pygmaeus, P. hanaki, and P. nathusii. The Y-shaped baculum in all studied Pipistrellus species has a proximal base with two club-shaped branches, a long slender shaft, and a forked distal tip. The branches contain a medullary cavity of variable size, which tapers into a central canal of variable length in the proximal baculum shaft. Both are surrounded by a lamellar and a woven bone layer and contain fatty marrow and blood vessels. The distal shaft consists of woven bone only, without a vascular canal. The proximal ends of the branches are connected with the tunica albuginea of the corpora cavernosa via entheses. In the penis shaft, the corpus spongiosum-surrounded urethra lies in a ventral grove of the corpora cavernosa, and continues in the glans under the baculum. The glans penis predominantly comprises an enlarged corpus spongiosum, which surrounds urethra and baculum. In the 12 studied juvenile and subadult P. pipistrellus specimens the proximal branches of the baculum were shorter and without marrow cavity, while shaft and distal tip appeared already fully developed. The present combination with light microscopic images from one species enabled a more reliable interpretation of histomorphological structures in the µCT-images from all four Pipistrellus species., (© 2015 Wiley Periodicals, Inc.)

Illustrations of penis morphology are essential components of species descriptions for harvestmen belonging to the suborder Laniatores. Male genitalia are important sources of taxonomic characters and are generally assumed to exhibit relatively little intraspecific variation. In contrast, descriptions of female reproductive morphology are rarely included in taxonomic descriptions of laniatorean harvestmen. As a result, relatively little is known about variation in the external features of the ovipositor. In this study, we used scanning electron microscopy to examine variation in male and female reproductive morphology among three species of harvestmen that are members of the superfamily Gonyleptoidea. Specifically, we examined the microanatomy of penises and ovipositors of Cynortula granulata (Cosmetidae), Phareicranaus calcariferus (Cranaidae), and Rhopalocranaus albilineatus (Manaosbiidae). Our results support the general observation that male reproductive morphology is conservative and displays little intraspecific variation. We observed considerable intraspecific variation in the number and shape of marginal setae on the ventral plate of the penis, but little or no variation in the morphology of the distal border of the ventral plate or the shape of the glans penis or stylus. With respect to female genitalia, we observed considerable intraspecific variation in the number of peripheral setae on the distal tip of the ovipositor. We also observed interspecific variation in the morphology of the peripheral setae (surface of the shaft and at shape of the distal tip), the distribution and morphology of smaller setae on the external surface of the ovipositor, and the surface texture of the external lobes. Our results indicate that there are several features associated with ovipositor morphology among laniatorean harvestmen that may represent potentially informative taxonomic characters., (Copyright © 2013 Wiley Periodicals, Inc.)

Objective: Current reference range values for fetal penile growth are based on length measurements. However, methodologies for measuring penile length differ among studies and from the standard technique used in children. We propose that the measurement of penile width may aid in its evaluation. The aim of the study was to create normograms for penile length and width., Methods: A prospective cross-sectional design was used. One hundred male fetuses at 22 to 36 gestational weeks were included. On ultrasound examination, penile length was measured from tip to base, where the penis joins the scrotum. Penile width was measured at the widest point across the penis. Reference values for the 5th and 95th percentiles were calculated for each gestational week., Results: There was a good correlation between gestational age and penile length (R(2) = 0.606) and width (R(2) = 0.683). The percentile of fetal weight estimation independently affected penile length and width. The interobserver correlation coefficient was 0.939 for length and 0.909 for width., Conclusion: Reference range values of fetal penile length and width are presented for 22 to 36 weeks of gestation. These values correlate to gestational age and estimated fetal weight percentile. These reference range measurements may help the evaluation of suspected micropenis., (© 2012 John Wiley & Sons, Ltd.)

The extravagance and diversity of external genitalia have been well characterized in male primates; however, much less is known about sex differences or variation in female form. Our study represents a departure from traditional investigations of primate reproductive anatomy because we 1) focus on external rather than internal genitalia, 2) measure both male and female structures, and 3) examine a strepsirrhine rather than an anthropoid primate. The subjects for morphological study were 21 reproductively intact, adult ring-tailed lemurs (Lemur catta), including 10 females and 11 males, two of which (one per sex) subsequently died of natural causes and also served as specimens for gross anatomical dissection. Male external genitalia presented a typical masculine configuration, with a complex distal penile morphology. In contrast, females were unusual among mammals, presenting an enlarged, pendulous external clitoris, tunneled by the urethra. Females had a shorter anogenital distance and a larger urethral meatus than did males, but organ diameter and circumference showed no sex differences. Dissection confirmed these characterizations. Noteworthy in the male were the presence of a "levator penis" muscle and discontinuity in the corpus spongiosum along the penile shaft; noteworthy in the female were an elongated clitoral shaft and glans clitoridis. The female urethra, while incorporated within the clitoral body, was not surrounded by erectile tissue, as we detected no corpus spongiosum. The os clitoridis was 43% the length and 24% the height of the os penis. On the basis of these first detailed descriptions of strepsirrhine external genitalia (for either sex), we characterize those of the female ring-tailed lemur as moderately "masculinized." Our results highlight certain morphological similarities and differences between ring-tailed lemurs and the most male-like of female mammals, the spotted hyena (Crocuta crocuta), and call attention to a potential hormonal mechanism of "masculinization" in female lemur development., (Copyright (c) 2007 Wiley-Liss, Inc.)

The number of penises vary in the insect suborder Forficulina (order Dermaptera; earwigs). Males of the families Diplatyidae, Pigidicranidae, Anisolabididae, Apachyidae, and Labiduridae have two penises (right and left), while those of the Spongipohridae, Chelisochidae, and Forficulidae have a single penis. The proposed phylogenetic relationships among these families suggest that the single-penis families evolved from an ancestor possessing two penises. To date, examinations of double-penis earwig species have found that only a single penis is used per single copulation. These diversities in structural and behavioral aspects of genitalia raises the following intriguing questions: How are the two penises used? Why did a penis degenerate in several earwig families, and which one was lost? To address these questions, structural and behavioral asymmetries were examined in detail for a representative species Labidura riparia (Labiduridae). Although there was no detectable morphological differentiation between the right and left penises, male L. riparia predominantly used the right one for insemination. This significant "right-handedness" developed without any experience of mating and was also manifested in the resting postures of the two penises when not engaged in copulation. However, surgical ablation of the right penis did not influence the insemination capacity of males. In wild-caught males, only about 10% were left-handed; within this group, abnormalities were frequently observed in the right penis. These lines of evidence indicate that the left penis is merely a spare intromittent organ, which most L. riparia males are likely never to use. Additional observations of five species of single-penis families revealed that the left penis degenerated in the common ancestor of this group. Considering the proposed sister relationship between the Labiduridae and the single-penis families, it is possible that such behavioral asymmetries in penis' use, as observed in L. riparia, are parental to the evolutionary degeneration of the infrequently used left penis., (Copyright 2006 Wiley-Liss, Inc.)

This study clarifies the identity and development of the male in the life cycle of Symbion pandora. The male is not produced directly by the feeding stage, as previously thought, but arises as a distinct individual from budding cells inside an intermediate stage named the Prometheus larva. The morphology and the development of the two distinct stages are described with light and electron microscopy. Furthermore, the following terminology is suggested to clearly distinguish between the different individuals: 1) the Prometheus larva, which is the free-swimming individual being produced inside the feeding stage; 2) the attached Prometheus larva on the feeding stage, which mostly degenerates following settlement, except for the internal budding cells; and 3) the dwarf male, which is the ciliated, sexually mature stage. The budding cells inside the attached Prometheus larva usually develop two internal dwarf males. Each dwarf male is heavily ciliated and has a well-developed nervous system with a relatively large brain, numerous gland and muscle cells, testis with bundles of sperm, and one penial structure. The male lacks a gut, as in the other free stages in the life cycle of Symbion pandora. This study also indicates that the dwarf male is freed from the attached Prometheus larva. Copulation, which has not been observed yet, probably takes place between a free-swimming male and the female, either while the female is released or afterwards., (Copyright 2003 Wiley-Liss, Inc.)

1. In normal mice, the distribution of adrenergic, cholinergic, some peptidergic, and neuronal nitric oxide synthase (nNOS)-containing nerves were investigated. Functional in vitro correlates were obtained. An in vivo model was developed in which erectile haemodynamics in response to drugs or nerve-stimulation were studied. 2. Immunoreactivities for vesicular acetylcholine transporter protein (VAChT), nNOS-, and vasoactive intestinal polypeptide (VIP), co-existed in nerve fibres and terminal varicosities. Immunoreactivities for neuropeptide Y (NPY) and tyrosine hydroxylase (TH) were found in the same nerve structures. 3. Chemical sympathectomy abolished TH- and NPY-IR nerve structures in cavernous smooth muscle bundles. The distribution of calcitonin gene-related peptide (CGRP)-, nNOS-, VAChT- and VIP-IR nerve structures was unchanged. 4. In endothelial cells of the central and helicine arteries, veins and venules, intense immunoreactivity for endothelial NOS (eNOS) was observed. No distinct eNOS-IR cells were found lining the cavernous sinusoids. 5. In vitro, nerve-induced relaxations were verified, and endothelial NO/cyclic GMP-mediated relaxant responses were established. VIP and CGRP had small relaxant effects. A functioning adenylate cyclase/cyclic AMP pathway was confirmed. 6. Neuronal excitatory responses were abolished by prazosin, or forskolin. VIP and CGRP counteracted contractions, whereas NPY and scopolamine enhanced excitatory responses. 7. In vivo, erectile responses were significantly attenuated by L-NAME (50 mg kg(-1)) and facilitated by sildenafil (200 microg kg(-1)). 8. It is concluded that the mouse is a suitable model for studies of erectile mechanisms in vitro and in vivo.

The baculum is a nonappendicular bone found in the glans tissue of members of five orders of mammals. Its function during copulation is unknown. Anatomical examination of the baculum and corpus cavernosum in the Norway rat (Rattus norvegicus) shows that the two structures are connected by a layer of fibrocartilage, and that the distal tip of the corpus cavernosum swells during erection to surround the proximal end of the baculum. Microradiographs of bacula from sexually experienced males show that regions of the bone may be remodeling; these data suggest that the baculum is load-bearing. On the basis of this anatomy, I propose that the baculum increases the overall flexural stiffness of the penis during copulation by transferring bending and compressive forces from the distal end of the glans to the tensile wall of the corpus cavernosum. Forces on the distal end of the penis during copulation press the baculum against the corpus cavernosum, reducing its internal volume and increasing intracavernosal pressure and corpus cavernosum wall strains. Because the wall of the erect corpus cavernosum is reinforced with inextensible collagen fibers, an increase in wall strain will also increase wall tissue stiffness, and thereby increase the flexural stiffness of the corpus cavernosum., (Copyright 2000 Wiley-Liss, Inc.)

Examination of histological sections from flaccid and artificially erected nine-banded armadillo (Dasypus novemcinctus) penises confirms that the mammalian corpus cavernosum is the first known biological hydrostat reinforced by collagen fibers arranged at 0 degree and 90 degrees to its long axis. The morphology of this axial orthogonal fiber array affects the mechanical behavior of mammalian penises during erection and copulation. Specifically, the axial orthogonal array gives the erect penis a reproducible shape, maximum size and resistance to tensile, compressive, and bending forces. These features are more appropriate for the mechanical regime associated with copulation than those found in structures reinforced by crossed-helical fibers, although the axial orthogonal array also gives the corpus cavernosum a tendency to fail by kinking. Crimped collagen fibers in the flaccid array as well as three-dimensional folding of the wall in the flaccid corpus cavernosum allow the structure to expand during erection.

Background: The extension of the female corpus spongiosum is subject to controversy. The anterior continuation of the vestibular bulbs, or pars intermedia, is not commonly recognized as part of the corpus spongiosum. Some authors deny this part of the corpus spongiosum exists in females., Material and Methods: To investigate this controversy, anatomic and histologic studies were performed of the female corpus spongiosum. The specimens were taken from female-to-male transsexual surgical patients and from fresh female cadavers. They were compared to surgically amputated penises to establish the similarity in male and female anatomy. RESULTS--CONCLUSIONS. The female corpus spongiosum is proven to extend anteriorly from the bilateral vestibular bulbs to terminate as the enlarged glans clitoridis. This latter structure also consists of spongious tissue. The spongiosum is hypertrophied in hormonally treated female-to-male transsexuals. The cleft vulvar anatomy is homologue to its non-cleft male counterpart.

Twenty penis from normal boars were injected with various media at known reservoir pressures and examined by radiography, dissection, maceration, clearing and sectioning. Injections into the corpus spongiosum penis (csp) produced dorsal deviation and clockwise spiral twisting. The ccp was traversed by a system of large longitudinal cavernous spaces. The csp consisted of one large vascular space, its walls joined by trabeculae which were close together ventrally and further apart dorsally. The corpus spongiosum glandis (csg) was a vascular network within the penile integument communicating with the csp by fine vascular spaces around the urethral orifice. The penile arteries and veins were supplied and drained by the internal pudendal vessels. The ccp was drained from its crura by the v profunda penis but no venous drainage of this cavernous body was demonstrated within the body of the penis. The csp was drained from its bulb by the v bulbi penis; its distal extremity was drained by two large veins which ran proximally enclosed by the tunica albuginea of the csp. The right vein was always much larger than the left vein and at the sigmoid flexure the two united to form the right tributary of the v dorsalis penis. The csg and the entire penile integument were drained by the left tributary of the v dorsalis penis; the csg was also drained by one or both of the ventral veins of the csp. Blood from the scrotum was drained by the v circumflexa perinealis and v perinealis ventralis into the v dorsalis penis and v penis. A large dorsal lymphatic vessel drained lymph from the body of the penis into the pelvic lymph nodes. No connections with the superficial inguinal lyphocentres were identified.

Illustrations in some anatomy textbooks purporting to be left lateral views of the organ are in fact right lateral views. The origin of this error is discussed. The variability in normal shape is described in 55 living bulls and 20 excised specimens from bulls of different breeds. The importance of a correct understanding of normal anatomy in clinical examination and surgery of the bovine penis is emphasised.