Glans penis

This article is about the glans penis. For other uses, see glans.

"Bellend" redirects here. For the English village, see Bell End.

In male human anatomy, the glans penis or penile glans,^[1] commonly referred to as the glans, (/ɡlænz/; from Latin glans meaning "acorn")^[2] is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and primary anatomical source of sexual pleasure.^[3][4] The glans penis is present in the male reproductive organs of humans and most other mammals where it may appear smooth, spiny, elongated or divided.^[5] It is externally lined with mucosal tissue, which creates a smooth texture and glossy appearance. In humans, the glans is located over the distal ends of the corpora cavernosa and is a continuation of the corpus spongiosum of the penis. At the summit appears the urinary meatus and at the base forms the corona glandis. An elastic band of tissue, known as the frenulum, runs on its ventral surface. In men who are not circumcised, it is completely or partially covered by a fold of skin called the foreskin. In adults, the foreskin can generally be retracted over and past the glans manually or sometimes automatically during an erection.^[6]

Glans penis
Human penile glans (dorsal view)
Glans (ventral view)
Details
Precursor	Genital tubercle
Part of	Penis
System	Urogenital system
Artery	Dorsal artery of the penis
Vein	Dorsal veins of the penis
Nerve	Dorsal nerve of the penis
Identifiers
Latin	glans penis
TA98	A09.4.01.007
TA2	3668
FMA	18247
Anatomical terminology [edit on Wikidata]

The glans penis develops as the terminal end of the genital tubercle during the embryonic development of the male fetus. The tubercle is present in the embryos of both sexes as an outgrowth in the caudal region that later develops into a primordial phallus. Exposure to male hormones (androgens) initiates the tubercle's development into a penis making the glans penis anatomically homologous to the clitoral glans in females.^[7][8]

The glans is more commonly known as the "head" or the "tip" of the penis, and colloquially referred to in British English and Irish English as the "bellend".

Internal anatomy of human glans penis:

1. Fascia penis
2. Corpus cavernosum
3. Coronal sulcus
4. Corona of glans
5. Foreskin
6. Glans penis
7. Meatus of the urethra
8. Navicular fossa of male urethra
9. Tunica albuginea of penis
10. Corpus spongiosum
11. Urethra

Structure

Diagram of the arteries of the penis and its glans

The glans penis as the expansion of the corpus spongiosum

The glans penis is a body of spongy erectile tissue that is moulded on the rounded ends of the two corpora cavernosa penis,^[9] extending farther on their upper than on their lower surfaces. It is the expanded cap of the corpus spongiosum,^[10] a sponge-like region that surrounds the male urethra within the penis maintaining it as a viable channel for ejaculation.^[11] The glans is covered by a stratified squamous epithelium and a dense layer of connective tissue equivalent to the dermis of typical skin.^[12] The papillary layer of the dermis blends into the dense connective tissue forming the tunica albuginea of the corpus spongiosum behind the glans.^[12] The external lining with mucosal tissue is responsible for its typical smooth texture and appearance.

The increase of arterial flow during erection fills the erectile tissue with blood causing the glans to grow in size and sensitivity.^[13] While the penis is rigid when erect, the glans itself remains slightly softer.^[14] The soft cushiony texture of the glans absorbs impact during rigorous instances of copulation.^[15] The proportional size of the glans penis can vary among males. While the shape of the glans is typically acorn-like, in some men it might be wider in circumference than the shaft, giving the penis a mushroom-like appearance, while in others it might be narrower and more akin to a probe in shape. Some researchers have suggested that the glans has evolved to become acorn-, mushroom- or cone-shaped so that during copulation it acts to remove any semen still there from previous sex partners, but this is not supported when looking at primate relatives who have different mating behaviors.^[16][17]

At the summit of the glans is the slit-like vertical external urethral orifice, called the urinary meatus, through which urine, semen and pre-ejaculatory fluid exit the penis. The circumference of the base of the glans forms a rounded projecting border, the corona glandis, overhanging a deep retroglandular groove known as the coronal sulcus. Behind the corona is the neck of the penis, which separates the glans and the penile shaft. Ventrally, the two glans wings merge on the midline forming the septum glandis and a triangle or a V-shaped area under it. The frenulum is the highly vascularized elastic band of tissue located on the underside of the glans that connects the foreskin to the head of the penis. The frenulum is supple enough to allow the retraction of the foreskin over the glans and pull it back when the erection is gone.^[18] In flaccid state, it tightens to narrow the foreskin opening.^[19]

Innervation

The glans and the frenulum are innervated by the bilateral dorsal nerve of the penis and the perineal nerve, both divisions of the pudendal nerve.^[20] Branches of the dorsal nerve extend through the glans ventrolaterally displaying a three-dimensional innervation pattern.^[20][21] The main branches form smaller bundles of nerves that expand outwards into the tissue of the glans.^[20] The rich innervation of the glans penis reveals its function as a primary anatomical source of male sexual pleasure.^[4][21][22] Yang & Bradley argue; "the distinct pattern of innervation of the glans emphasizes its role as a sensory structure".^[4] While Yang & Bradley's (1998) report "showed no areas in the glans to be more densely innervated than others.",^[4] Halata & Munger (1986) report that the density of several nerve terminals is greatest in the corona glandis.^[12]

Halata & Spathe (1997) reported; "the glans penis contains a predominance of free nerve endings, numerous genital end bulbs and rarely Pacinian and Ruffinian corpuscles. Merkel nerve endings and Meissner's corpuscles (mechanoreceptors typically found in thick glabrous skin) are not present".^[23] The genital end bulbs, that are present throughout the glans, are most numerous in the corona and near the frenulum.^[12] Simple, Pacinian and Ruffinian corpuscles are identified predominantly in the corona glandis. The most numerous nerve terminals are free nerve endings present in almost every dermal papilla of the glans, as well as scattered throughout the deeper dermis.^[12]

Blood supply

The glans penis receives blood from the internal pudental artery through its branch, the dorsal artery of the penis, which also supplies the foreskin, and the penile shaft.^[24] Behind the corona, the terminal branches of the dorsal arteries anastomose with the axial arteries through perforating branches before they end in the glans.^[25] Branches of the dorsal artery curve around each side of the distal shaft to enter the glans and the frenulum ventrally.^[26] Venous drainage of the penis begins at the base of the glans. Small tributaries deriving from the corona form a venous plexus at the neck of the penis, known as the retro-coronal, or retro-balanic, plexus.^[27] Smaller paired venules run into the frenulum and the glans from its ventral surface.^[28] The deep dorsal vein, one of the two dorsal veins of the penis, serves as a common vessel receiving blood drained from the glans and the two corpora cavernosa through the circumflex veins that surround them.^[27][29]

Foreskin

The glans is completely or partially covered by a double-layered fold of skin, known as the foreskin. In adults, glans exposure can be easily achieved by manual retraction of the foreskin or sometimes automatically during erection. The degree of automatic foreskin retraction varies considerably depending on the foreskin length. The foreskin can be characterized as long when the preputial orifice extends beyond the glans during erection or medium when the orifice is located around the meatus.^[30] The primary purpose of the foreskin is considered to be the covering of the glans and the urinary meatus,^[31][32] while also maintaining the mucosa in a moist environment.^[33] Foreskin rectractability gradually increases with age. In infancy the foreskin is fused to the glans,^[34] it remains non retractable in early childhood and it continues to be tight during preadolescence.^[35] The skin begins to loosen up significantly during puberty allowing the glans to be completely exposed when needed. By the age of eighteen most boys will have a fully retractable foreskin.^[36]

In some cases, for cultural, medical, or prophylactic reasons some men undergo circumcision or were circumcised as infants, a procedure where the foreskin is partially or completely removed from the penis.^[19] The glans of circumcised men remains fully exposed and dry. Several studies have suggested the glans is generally equally sensitive in both circumcised and uncircumcised penises.^[37][38][39]

Development

Main article: Development of the reproductive system

Development of external genitalia in the male embryo

The glans develops as the terminal end of a phallic structure, called the genital tubercle, which forms in the embryo regardless of sex during the early weeks of pregnancy.^[7] Initially undifferentiated, the tubercle develops into a penis during the development of the reproductive system depending on the exposure to male hormones, such as androgens. In mammals, sexual differentiation is determined by the sperm that carries either an X or a Y (male) chromosome.^[40] The Y chromosome contains a sex-determining gene (SRY) that encodes a transcription factor for the protein TDF (testis determining factor) and triggers the creation of testosterone for the embryo's development into a male.^[8][41]

Although the sex of the infant is determined from the moment of conception,^[7] the complete external differentiation of the organs begins about eight or nine weeks after conception.^[42] Some sources state that the process will be completed by the twelfth week,^[43][44] while others state that it is clearly evident by the thirteenth week and that the sex organs are fully developed by the sixteenth week.^[8]

Both the penis and clitoris develop from the same tissues that become the glans and shaft of the penis and this shared embryonic origin makes these two organs homologous (different versions of the same structure).^[8][45] In the female fetus the absence of testosterone will stop the growth of the phallus causing the tubercle to shrink and form the clitoris. In the male fetus the presence of a Y chromosome leads to the development of the testes, which secrete a large amount of hormones called androgens. These hormones will cause the masculinization of the phenotypically indifferent organs.^[7] When exposed to testosterone, the genital tubercle elongates to form the penis. By fusion of the urogenital folds—elongated spindle-shaped structures that contribute to the formation of the urethral groove on the belly aspect of the genital tubercle—the urogenital sinus closes completely to form the spongy urethra and the labioscrotal swellings unite to form the scrotum.^[46][8] The secretion of testosterone during this phase plays a decisive role in the final shaping of the penis. After birth, testosterone levels drop significantly until puberty.

Clinical significance

The epithelium of the glans penis consists of mucosal tissue. Birley et al. report that excessive washing with soap may dry the mucous membrane which covers the glans penis and cause non-specific dermatitis. The condition is described as an inflammation of the skin, often caused by an irritating substance or a contact allergy. Sensitivity to chemicals in certain products can cause an allergic reaction, including irritation, itching and rash.^[47]

Inflammation of the glans penis is known as balanitis. It is a treatable condition that occurs in about 3–11% of males (up to 35% of diabetic males). Edwards reported that it is generally more common in males who have poor hygiene habits or have not been circumcised. It has many causes, including irritation or infection with a wide variety of pathogens. Symptoms of balanitis may appear suddenly or develop gradually. They might include pain, irritation, redness or red patches on the glans penis. Careful identification of the cause with the aid of patient history, physical examination, swabs and cultures, and biopsy are essential in order to determine the proper treatment.^[48]

The meatus (opening) of the urethra located at the tip of the glans might become subject to meatal stenosis, a condition mostly seen as a late complication of circumcision. It occurs in about 2–20% of circumcised boys^[49][50] and it is rarely seen in uncircumcised men.^[51] It is characterized by a narrowing of the meatus, which might cause sudden or often urges to urinate and burning during the process.^[51]

For some individuals who experience difficulty in achieving full glanular engorgement of glans penis, they may be diagnosed with soft glans syndrome (glans insufficiency syndrome). It is often undiagnosed in the general population due to the lack of a standardized nomenclature.^[52][53]

Other animals

Mammals

Carnivores

Male felids are able to urinate backwards by curving the tip of the glans penis backward.^[54][55] In cats, the glans penis is covered with spines. Penile spines also occur on the glans of male and female spotted hyenas.^[54] In male dogs the glans penis is smooth and consists of two parts called the bulbus glandis and pars longa glandis.^[56] The glans of a fossa's penis extends about halfway down the shaft and is spiny except at the tip. In comparison, the glans of felids is short and spiny, while that of viverrids is smooth and long.^[57]

Rodents

The glans penis of the marsh rice rat is long and robust,^[58] averaging 7.3 mm (0.29 in) long and 4.6 mm (0.18 in) broad.^[59] Winkelmann's mouse can most readily be distinguished from its close relatives by its partially corrugated glans penis.^[60] In Thomasomys ucucha, the glans penis is rounded, short, and small and is superficially divided into left and right halves by a trough at the top and a ridge at the bottom. Most of the glans is covered with spines, except for an area near the tip.^[61] The glans penis of a male cape ground squirrel is large with a prominent baculum.^[62]

Perissodactyls

When erect, the glans of a horse's penis increases by 3 to 4 times. The urethra opens within the urethral fossa, a small pouch at the distal end of the glans.^[63] Unlike the human glans, the glans of a horse's penis extends backwards on its shaft.^{[64][65][66][67][68][69][70][71][72]}

Marsupials, monotremes and bats

The shape of the glans varies among different marsupial species.^[73][74][75] In most marsupials, the glans is divided, but male macropods have an undivided glans penis.^[5]

The glans penis is also divided into two parts in platypuses and echidnas.^[76][77]

Males of Racey's pipistrelle bat have a narrow, egg-shaped glans penis.^[78]

See also

• Corona of glans penis
• Pearly penile papules

References

1. Greenburg, Jerrold S.; Bruess, Clint E. (2016). Exploring the Dimensions of Human Sexuality. Jones & Bartlett Learning. p. 267. ISBN 978-1-28408-154-1.
2. Hodgson, Charles (2015). Carnal Knowledge: A Navel Gazer's Dictionary of Anatomy, Etymology, and Trivia. St. Martin's Publishing Group. p. 179. ISBN 978-1-46689-043-5.
3. Olausson, Håkan; Wessberg, Johan; Morrison, India (2016). Affective Touch and the Neurophysiology of CT Afferents. Springer Science+Business Media. p. 305. ISBN 978-1-4939-6418-5. ...the most pleasurable of all body parts when stimulated sexually: the glans (or tip) of the penis.
4. Yang, C. C.; W.E. Bradley (July 1998). "Neuroanatomy of the penile portion of the human dorsal nerve of the penis". British Journal of Urology. 82 (1): 109–13. doi:10.1046/j.1464-410x.1998.00669.x. PMID 9698671.
5. Renfree, Marilyn; Hugh Tyndale-Biscoe (1987-01-30). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 978-0-521-33792-2. Retrieved 5 May 2013.
6. Keenan-Lindsay, Lisa; Sams, Cheryl; O'Connor, Constance; Perry, Shannon; Hockenberry, Marilyn; Leonard Lowdermilk, Deitra; Wilson, David (December 17, 2021). Maternal Child Nursing Care in Canada. Elsevier Health Sciences. p. 501. ISBN 978-0-323-75920-5.
7. W.George, D.Wilson, Fredrick, Jean (1984). "2 - Sexual Differentiation". Fetal Physiology and Medicine (Second, Revised ed.). Butterworth-Heinemann. pp. 57–79. doi:10.1016/B978-0-407-00366-8.50008-3. ISBN 978-0-407-00366-8. Archived from the original on 2022-09-22. Retrieved 2022-09-23.{{cite book}}: CS1 maint: multiple names: authors list (link)
8. Schünke, Michael; Schulte, Erik; Lamperti, Edward D.; Schumacher, Udo (2006). Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. ISBN 978-1-58890-387-7.
9. Schatten, Heide; Constantinescu, Gheorghe M. (21 March 2008). Comparative Reproductive Biology. John Wiley & Sons. ISBN 978-0-470-39025-2.
10. Lee, Shin-Hyo; Ha, Tae-Jun; Koh, Ki-Seok; Song, Wu-Chul (2019). "Ligamentous structures in human glans penis". Journal of Anatomy. 234 (1): 83–88. doi:10.1111/joa.12896. PMC 6284436. PMID 30450557.
11. "penis | Description, Anatomy, & Physiology | Britannica". www.britannica.com. Archived from the original on 2022-09-24. Retrieved 2022-09-24.
12. Halata, Z.; Munger, B. L. (1986-04-23). "The neuroanatomical basis for the protopathic sensibility of the human glans penis". Brain Research. 371 (2): 205–230. doi:10.1016/0006-8993(86)90357-4. ISSN 0006-8993. PMID 3697758. S2CID 23781274. Archived from the original on 2022-09-25. Retrieved 2022-09-25.
13. Dean, Robert C.; Lue, Tom F. (2005–2011). "Physiology of Penile Erection and Pathophysiology of Erectile Dysfunction". The Urologic Clinics of North America. 32 (4): 379–v. doi:10.1016/j.ucl.2005.08.007. ISSN 0094-0143. PMC 1351051. PMID 16291031.
14. Hsu, Geng-Long; Lu, Hsiu-Chen (2018-01-01), "Penis Structure—Erection", in Skinner, Michael K. (ed.), Encyclopedia of Reproduction (Second Edition), Oxford: Academic Press, pp. 367–375, ISBN 978-0-12-815145-7, retrieved 2023-07-06
15. HSU, G‐L., et al. "The distribution of elastic fibrous elements within the human penis." BJU International 73.5 (1994): 566-571.
16. Gallup, Gordon G., et al. "The human penis as a semen displacement device Archived 2018-02-13 at the Wayback Machine." Evolution and Human Behavior 24.4 (2003): 277-289
17. Dixson, Alan F. (2009). Sexual Selection and the Origins of Human Mating Systems. OUP Oxford. p. 68. ISBN 978-0-19-156973-9.
18. "Penis Frenulum: Location, Function & Conditions". Cleveland Clinic. Archived from the original on 2022-09-24. Retrieved 2022-09-24.
19. "Male circumcision: Global trends and determinants of prevalence, safety and acceptability" (PDF). World Health Organization. 2007. Archived (PDF) from the original on 2015-07-15. Retrieved 2009-06-12.
20. Weech, David; Ameer, Muhammad Atif; Ashurst, John V. (2022), "Anatomy, Abdomen and Pelvis, Penis Dorsal Nerve", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30247841, archived from the original on 2023-04-05, retrieved 2022-09-26
21. Yang, Claire C.; Bradley, William E. (1999-01-01). "Innervation of the human glans penis". Journal of Urology. 161 (1): 97–102. doi:10.1016/S0022-5347(01)62075-5. PMID 10037378. Archived from the original on 2021-11-21. Retrieved 2022-09-24.
22. Greenberg, Jerrold; Bruess, Clint; Conklin, Sarah (2010-03-10). Exploring the Dimensions of Human Sexuality. Jones & Bartlett Learning. p. 132. ISBN 978-0-7637-7660-2.
23. Halata, Zdenek; A. Spaethe (1997). "Sensory Innervation of the Human Penis". The Fate of the Male Germ Cell. Advances in Experimental Medicine and Biology. Vol. 424. pp. 265–6. doi:10.1007/978-1-4615-5913-9_48. ISBN 978-0-306-45696-1. PMID 9361804. Archived from the original on 2006-06-20. Retrieved 2006-07-07.
24. Clement, Pierre; Giuliano, Francois (2015). "3 - Anatomy and physiology of genital organs – men". Handbook of Clinical Neurology. Vol. 130. Elsevier. pp. 19–37. doi:10.1016/B978-0-444-63247-0.00003-1. ISBN 978-0-444-63247-0. ISSN 0072-9752. PMID 26003237. Archived from the original on 2020-10-17. Retrieved 2022-10-30.
25. Quartey, J. K.M. (2006), Schreiter, F.; Jordan, G.H. (eds.), "Anatomy and Blood Supply of the Urethra and Penis", Urethral Reconstructive Surgery, Berlin, Heidelberg: Springer, p. 14, doi:10.1007/3-540-29385-x_3, ISBN 978-3-540-29385-9, retrieved 2022-10-29
26. Hinman, F. (1991). "The blood supply to preputial island flaps". The Journal of Urology. 145 (6): 1232–1235. doi:10.1016/s0022-5347(17)38584-1. ISSN 0022-5347. PMID 2033699. Archived from the original on 2022-11-09. Retrieved 2023-01-27.
27. Quartey, J. K.M. (2006), Schreiter, F.; Jordan, G.H. (eds.), "Anatomy and Blood Supply of the Urethra and Penis", Urethral Reconstructive Surgery, Berlin, Heidelberg: Springer, p. 16, doi:10.1007/3-540-29385-x_3, ISBN 978-3-540-29385-9, retrieved 2022-10-29
28. Gyftopoulos, Kostis I. (2018). "Meatal stenosis after surgical correction of short frenulum: Is the "pull-and-burn" method the way to go?". Urology Annals. 10 (4): 354–357. doi:10.4103/UA.UA_25_18. ISSN 0974-7796. PMC 6194789. PMID 30386085.
29. Hsu, Geng-Long; Hsieh, Cheng-Hsing; Wen, Hsien-Sheng; Chen, Yi-Chang; Chen, Shyh-Chyan; Mok, Martin S. (2003-11-12). "Penile Venous Anatomy: An Additional Description and Its Clinical Implication". Journal of Andrology. 24 (6): 921–927. doi:10.1002/j.1939-4640.2003.tb03145.x. PMID 14581520.
30. Velazquez, Elsa F.; Bock, Adelaida; Soskin, Ana; Codas, Ricardo; Arbo, Manuel; Cubilla, Antonio L. (2003). "Preputial variability and preferential association of long phimotic foreskins with penile cancer: An anatomic comparative study of types of foreskin in a general population and cancer patients". The American Journal of Surgical Pathology. 27 (7): 994–998. doi:10.1097/00000478-200307000-00015. ISSN 0147-5185. PMID 12826892. S2CID 34091663. Archived from the original on 8 November 2022. Retrieved 29 October 2022.
31. Kirby R, Carson C, Kirby M (2009). Men's Health (3rd ed.). New York, NY: Informa Healthcare. p. 283. ISBN 978-1-4398-0807-8. OCLC 314774041.
32. Dobanovacki D, Lucić Prostran B, Sarac D, Antić J, Petković M, Lakić T (2012). "Prepuce in boys and adolescents: What when, and how?". Medicinski Pregled. 65 (7–8): 295–300. doi:10.2298/MPNS1208295D. PMID 22924249.
33. Cold, C.J.; Taylor, J.R. (1999). "The prepuce". BJU International. 83 (S1): 34–44. doi:10.1046/j.1464-410x.1999.0830s1034.x. ISSN 1464-410X. PMID 10349413.
34. Dave, Sumit; Afshar, Kourosh; Braga, Luis H.; Anderson, Peter (2018). "CUA guideline on the care of the normal foreskin and neonatal circumcision in Canadian infants". Canadian Urological Association Journal. 12 (2): E76–E99. doi:10.5489/cuaj.5033. ISSN 1920-1214. PMC 5937400. PMID 29381458. Archived from the original on 2022-10-28. Retrieved 2022-10-29. At birth, the inner foreskin is usually fused to the glans penis and should not be forcibly retracted
35. Dave, Sumit; Afshar, Kourosh; Braga, Luis H.; Anderson, Peter (2018). "CUA guideline on the care of the normal foreskin and neonatal circumcision in Canadian infants". Canadian Urological Association Journal. 12 (2): E76–E99. doi:10.5489/cuaj.5033. ISSN 1920-1214. PMC 5937400. PMID 29381458. Archived from the original on 2022-10-28. Retrieved 2022-10-29. ... the incidence of non-retractable physiological phimosis was 50% in grade 1 boys and decreased to 35% in grade 4 and 8% in grade 7 boys
36. McGregor, Thomas B.; Pike, John G.; Leonard, Michael P. (2007). "Pathologic and physiologic phimosis: Approach to the phimotic foreskin". Canadian Family Physician. 53 (3): 445–448. PMC 1949079. PMID 17872680. most foreskins will become retractile by adulthood.
37. Clifford B., Bleustein; Fogarty, James D.; Eckholdt, Haftan; Arezzo, Joseph C.; Melman, Arnold (April 2005). "Effect of neonatal circumcision on penile neurologic sensation". Urology. 65 (4): 773–777. doi:10.1016/j.urology.2004.11.007. PMID 15833526.
38. Bleustein, Clifford B.; Eckholdt, Haftan; Arezzo, Joseph C.; Melman, Arnold (2003). Effects of circumcision on male penile sensitivity. American Urological Association 98th Annual Meeting. Clinical Prostate Cancer. Vol. 2, no. 1. Chicago, IL. pp. 8–12. doi:10.1016/s1540-0352(11)70011-7. PMID 15046675. Archived from the original on February 11, 2023. Retrieved February 11, 2023.
39. Payne, Kimberley; Thaler, Lea; Kukkonen, Tuuli; Carrier, Serge; Binik, Yitzchak (May 2007). "Sensation and sexual arousal in circumcised and uncircumcised men". Journal of Sexual Medicine. 4 (3): 667–674. doi:10.1111/j.1743-6109.2007.00471.x. PMID 17419812.
40. Arulkumaran, Sabaratnam; Regan, Lesley; Papageorghiou, Aris; Monga, Ash; Farquharson, David (2011-06-23). Oxford Desk Reference: Obstetrics and Gynaecology. OUP Oxford. ISBN 978-0-19-162087-4.
41. Hake, Laura & O'Connor, Clare. "Genetic Mechanisms of Sex Determination | Learn Science at Scitable". nature.com. Archived from the original on 2017-08-19. Retrieved 2022-09-23.
42. Merz, Eberhard; Bahlmann, F. (2004). Ultrasound in Obstetrics and Gynecology. Vol. 1. Thieme Medical Publishers. ISBN 978-1-58890-147-7.
43. C.L.Lachelin, Gillian (1991). "Chapter 4 - Sexual differentiation". Introduction to Clinical Reproductive Endocrinology. Butterworth-Heinemann. pp. 36–41. doi:10.1016/B978-0-7506-1171-8.50008-8. ISBN 978-0-7506-1171-8. Archived from the original on 2022-09-22. Retrieved 2022-09-23.
44. Merz, Eberhard; Bahlmann, F. (2004). Ultrasound in Obstetrics and Gynecology. Vol. 1. Thieme Medical Publishers. ISBN 978-1-58890-147-7
45. Sloane, Ethel (2002). Biology of Women. Delmar Thomson Learning. ISBN 978-0-7668-1142-3.
46. Sloane, Ethel (2002). Biology of Women. Cengage Learning. ISBN 978-0-7668-1142-3. Archived from the original on 13 June 2013. Retrieved 27 October 2015.
47. "Contact Dermatitis: Irritants, Allergies, Symptoms & Treatment". Cleveland Clinic. Archived from the original on 2022-09-25. Retrieved 2022-09-25.
48. "Balanitis: Types, Symptoms, Causes, Treatments, Prevention & Relief". Cleveland Clinic. Archived from the original on 2022-09-25. Retrieved 2022-09-25.
49. Sorokan SK, Finlay JC, Jefferies AL (2015). "Newborn male circumcision". Paediatrics & Child Health. 20 (6): 311–320. doi:10.1093/pch/20.6.311. PMC 4578472. PMID 26435672. Archived from the original on 30 October 2019. Retrieved 20 October 2017.
50. Koenig JF (22 September 2016). "Meatal stenosis". EMedicine. Archived from the original on 12 September 2017. Retrieved 2 October 2017.
51. "Meatal Stenosis: Symptoms, Diagnosis & Treatment - Urology Care Foundation". urologyhealth.org. Archived from the original on 2022-09-25. Retrieved 2022-09-25.
52. "Glans Insufficiency Syndrome | CSM". Retrieved 2023-12-24.
53. "Soft Glans / Cold Glans / Glans Insufficiency Syndrome". www.sdsm.info. Retrieved 2023-12-24.
54. Ewer, R. F. (1973). The Carnivores. Cornell University Press. pp. 116–. ISBN 978-0-8014-8493-3. Retrieved 8 February 2013.
55. Mathur, Reena (2010). Animal Behaviour 3/e. Rastogi Publications. ISBN 978-81-7133-747-7. Retrieved 10 February 2013.^{[permanent dead link‍]}
56. Evans, Howard E.; de Lahunta, Alexander (7 August 2013). Miller's Anatomy of the Dog. Elsevier Health Sciences. ISBN 978-0-323-26623-9.
57. Köhncke, M.; Leonhardt, K. (1986). "Cryptoprocta ferox" (PDF). Mammalian Species (254): 1–5. doi:10.2307/3503919. JSTOR 3503919. Archived (PDF) from the original on 21 June 2010. Retrieved 19 May 2010.
58. Hooper and Musser, 1964, p. 13
59. Hooper and Musser, 1964, table 1
60. Bradley, R.D.; Schmidley, D.J. (1987). "The glans penes and bacula in Latin American taxa of the Peromyscus boylii group". Journal of Mammalogy. 68 (3): 595–615. doi:10.2307/1381595. JSTOR 1381595.
61. Voss, 2003, p. 11
62. Skurski, D., J. Waterman. 2005. "Xerus inauris", Mammalian Species 781:1-4.
63. "The Stallion: Breeding Soundness Examination & Reproductive Anatomy". University of Wisconsin-Madison. Archived from the original on 2007-07-16. Retrieved 7 July 2007.
64. Mating Males: An Evolutionary Perspective on Mammalian Reproduction. Cambridge University Press. 30 June 2012. ISBN 978-1-107-00001-8. Retrieved 5 May 2013.
65. Bassert, Joanna M; McCurnin, Dennis M (2013-04-01). McCurnin's Clinical Textbook for Veterinary Technicians - Joanna M Bassert, Dennis M McCurnin - Google Boeken. Elsevier Health Sciences. ISBN 978-1-4557-2884-8. Retrieved 2013-08-16.
66. Research, Equine (2005-07-01). Horseman's Veterinary Encyclopedia, Revised and Updated - Equine Research - Google Boeken. Rowman & Littlefield. ISBN 978-0-7627-9451-5. Retrieved 2013-08-16.
67. Weese, Scott; Graham Munroe, Dr; Munroe, Graham (2011-03-15). Equine Clinical Medicine, Surgery and Reproduction - Graham Munroe BVSc (Hons) PhD Cert EO DESM Dip ECVS FRCVS, Scott Weese DVM DVSc DipACVIM - Google Boeken. CRC Press. ISBN 978-1-84076-608-0. Retrieved 2013-08-16.
68. König, Horst Erich; Hans-Georg, Hans-Georg; Bragulla, H (2007). Veterinary Anatomy of Domestic Mammals: Textbook and Colour Atlas - Google Boeken. Schattauer Verlag. ISBN 978-3-7945-2485-3. Retrieved 2013-08-16.
69. Hedge, Juliet (2004). Horse Conformation: Structure, Soundness, and Performance - Equine Research - Google Boeken. Lyons Press. ISBN 978-1-59228-487-0. Retrieved 2013-08-16.^{[permanent dead link‍]}
70. Evans, Warren J; Borton, Anthony; Hintz, Harold; Dale Van Vleck, L (1990-02-15). The Horse - Google Boeken. Macmillan. ISBN 978-0-7167-1811-6. Retrieved 2013-08-16.
71. Schatten, Heide; Constantinescu, Gheorghe M (2008-03-21). Comparative Reproductive Biology - Heide Schatten, Gheorghe M. Constantinescu - Google Boeken. John Wiley & Sons. ISBN 978-0-470-39025-2. Retrieved 2013-08-16.
72. McKinnon, Angus O; Squires, Edward L; Vaala, Wendy E; Varner, Dickson D (2011-07-05). Equine Reproduction - Google Boeken. John Wiley & Sons. ISBN 978-0-470-96187-2. Retrieved 2013-08-16.
73. Australian Mammal Society (December 1978). Australian Mammal Society. Australian Mammal Society. pp. 73–. Retrieved 25 December 2012.
74. Osgood, Wilfred Hudson; Herrick, Charles Judson (1921). A monographic study of the American marsupial, Caēnolestes …. University of Chicago. pp. 64–. Retrieved 25 December 2012.
75. The Urologic and Cutaneous Review. Urologic & Cutaneous Press. 1920. pp. 677–. Retrieved 25 December 2012.
76. Griffiths, Mervyn (2 December 2012). The Biology of the Monotremes. Elsevier Science. ISBN 978-0-323-15331-7.
77. Hyman, Libbie Henrietta (15 September 1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. ISBN 978-0-226-87013-7.
78. Bates et al., 2006, pp. 306–307

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