The os penis reported in some species of the mammalian orders was observed in the juvenile and adult penes of the friguvorous African bat, Eidolon helvum. The morphology of the os penis in Eidolon helvum differs from those observed in bat species and other mammalian orders. In the adult form it is large, disc-shaped and located at the distal segment of the penile organ. The proximal segment of the penis does not contain any bone. In the juvenile bat the os penis is made of two separate bones located longitudinally close to each other at the distal third of the penile tissue. The distal location in both the juvenile and the adult poses a question about the true function of this tissue. The bone may function in Eidolon helvum to support erection of the penis more for micturition than for intromission

Baxter-Grillo, Dorothea L

Caxton-Martins, Ademola E

Nwoha, Polycarp U

English

Via Medica Journals

153Polycarp Nwoha et al., The os penis of the frugivorous batFolia Morphol. Vol. 59, No. 3, pp. 153156Copyright ' 2000 Via MedicaISSN 00155659www.fm.viamedica.plO R I G I N A L  A R T I C L EAddress for correspondence: Polycarp Nwoha, Department of Anatomy and Cell Biology, Obaferai Awolowo University Ile-Ife, Nigeria,tel: +036 23 1444, fax: +036 23 1733, e-mail: pnwoha@oauife.edu.ngThe os penis of the frugivorous bat,Eidolon helvum (Kerr)Polycarp U Nwoha, Ademola E Caxton-Martins, Dorothea L Baxter-GrilloDepartment of Anatomy and Cell Biology, Obafemi Awolowo University, Ile-Ife, Nigeria[Received 23 May 2000; Revised 20 June 2000; Accepted 20 June 2000]The os penis reported in some species of the mammalian order was observed inthe juvenile and adult penes of the friguvorous African bat, Eidolon helvum. Themorphology of the os penis in Eidolon helvum differs from that observed in batspecies and other mammalian order. In the adult form it is large, disc-shapedand located at the distal segment of the penile organ. The proximal segment ofthe penis does not contain any bone. In the juvenile bat the os penis is made oftwo separate bones located longitudinally close to each other at the distal thirdof the penile tissue. The distal location in both the juvenile and the adult posesa question about the true function of this tissue. The bone may function inEidolon helvum to support erection of the penis more for micturition than forintromission.key words: os penis, Eidolon helvum, morphology, batINTRODUCTIONThe penis is composed mainly of erectile tissue and,when this is distended, the penis serves as an intro-mittent organ in copulation. The erectile tissue is dis-posed in three somewhat cylindrical columns: twocorpora cavernosa and the corpus spongiosum [6].Corpora cavernosa form the greater part of the bodyof the penis and are placed in the dorsolateral partof the organ. Corpus spongiosum terminates in frontas an expanded portion, the glans penis, which isdemarcated from the main mass of the corpus spon-giosum by a well-marked ridge called corona glan-dis. Corpus spongiosum is traversed throughoutits whole extent by the urethra [6]. Erection of thepenis is a very necessary prerequisite for the pen-etration of the vagina. The essential factor in erec-tion is active arteriolar dilatation in the corporaresulting in increasing pressure within the cavern-ous erectile tissue and obstruction to the venousoutflow, so adding to the distention of the erec-tile tissue [6].The os penis has been described in few mam-mals. Williams-Ashman and Reddi [18] stated that itis limited to some eutherian mammalian taxa. In ratit is described as having a distal segment made ofcartilage bone and a proximal segment made ofmembrane bone [1,5,11,12,16,17]. Cunha and Lung[3] and Iguchi et al. [7] have described the presenceof os penis and os clitoridis in mice. While the ospenis of the male mouse comprised proximal mem-brane and distal cartilaginous components the osclitoridis of the female comprised only membranebone. The os penis has also been reported in theAmerican mink and in dog [2,13]. Investigations ofa few species of chiroptera have revealed the os pe-nis in the Southeastern Australian little mastiff bat,Mormopterus planiceps [8], in the Niger Air Moun-tain Massif bats Otonycteris hemprichi and Pipes-trellus manus [4]. Os penis is present in some Amer-ican species of chiroptera but not in the leaf-nosedtemperate Southwestern United States bat, Macro-tus waterhousii, [9]. This means that the bone is not154Folia Morphol., 2000, Vol. 59, No. 3present in all species of bats. Hence, the need toinvestigate the bone in Eidolon helvum, a tropicalmegachiropteran fruit-eating bat, widely distribut-ed in most parts of Africa, on which no report is yetavailable. The proximal membranous segment of theos penis is present even at 1st day of post-natal lifein rat while the distal cartilagenous segment devel-ops later [15]. Rasmussen et al. [14] confirmed thatthe development of the distal segment is androgen-dependent and develops later in life when andro-gen expression is adequate for male maturity. Thismeans that the bone may not be present in the youngbat. Considering the fact that the os penis is report-ed to be absent in a male bat species [9] and repre-sented by a single centrally located bone in the adultOtonycteris hemprichi and Pipestrellus manus [4]there is need to study the morphology of this bonein the juvenile bat. The present study investigatedthe presence of the os penis in the juvenile and inthe adult Eidolon helvum.MATERIAL AND METHODSTwenty juvenile and twenty adult male megachi-ropteran, Eidolon helvum weighing approximately40 g and 180 g respectively, were used in this study.The bats were captured in their roosting colonies onthe campus of Obafemi Awolowo University, Ile-Ife,Nigeria and kept in the animal holdings of the De-partment of Anatomy and Cell Biology, Faculty ofHealth Sciences, Obafemi Awolowo University, Ile-Ife to recover from their injuries and acclimatise tolaboratory conditions. Whilst in the animal holdingsthey were fed regularly on fruits and provided waterad libitum. Each bat was decapitated and the peniscarefully dissected out for morphological study usingthe vital staining of Alizarin red S for calcium (bone)and according to the method of McGee-Russell [10].Alizarin red S stains newly formed bone tissue.RESULTSThe os penis was stained in the juvenile as well as inthe adult Eidolon helvum. In the juvenile Eidolon theos penis comprised two small bones, paddle-shapedand situated longitudinally in the distal third of thepenile organ, close to each other (Fig. 1). The proxi-mal and middle thirds of the penis showed no stain-ing for Alizarin red S. In the adult Eidolon helvumthe penile organ comprised two parts  a large distalportion and a narrow proximal portion. Alizarin redS stained bone tissue in the proximal segment. Thebone is single, large and disc-shaped, occupying al-most the entire distal portion. No tissue was stainedin the proximal portion (Fig. 2).Figure 1. Photograph of penis of juvenile Eidolon helvum (40 gbody weight). It shows two pieces of the os penis at the distalthird of the tissue (arrow). Staining with Alizarin red S. 1500 xDISCUSSIONThe presence of the os penis in Eidolon helvum sug-gests that this bone supports the penile organ. Thismay be necessary to improve the turgidity of thisorgan during erection. The morphology of the ospenis varies in different species of the mammalianorder. In rat [15] and in mice [5] it is longitudinaland represented by proximal membranous and dis-tal cartilaginous bones. In mastiff bat Krutzsch andCrichton [8] described it as a single greatly elongat-ed bone. In the Otonycteris hemprichi and Pipestrel-lus manus Fairon [4] noted the os penis as singleand centrally located in the penis. In the Eidolonhelvum, reported here, the os penis is single, disc-shaped and distally located. The various morpholo-gy and location of the os penis in the adult penileorgan suggest that the supporting function may vary155Polycarp Nwoha et al., The os penis of the frugivorous batfrom species to species. In some species of the samemammalian order this supporting function may notbe necessary. Krutzsch et al. [9] reported that thepenile organ of the bat Macrotus waterhousii lackedos penis and observed that this was in contrast toother temperate North American bats that had ospenis. Perhaps the nature of the erective tissue dif-fers in the species of bats and so needs to be inves-tigated.In rat the os penis develops as membrane boneeven at day 1 postnatal; the cartilaginous compo-nent develops later [15]. In mice the os penis devel-ops as membrane bone proximally at the 5th daypostnatal life and cartilaginous bone distally at the30th day postnatal life [7]. No report of the os penisin the juvenile of chiroptera is available. In the presentwork, in the juvenile Eidolon helvum, the os penis ispaired and distally located in the penile organ. It isnot known therefore whether the os penis in theEidolon is a membrane or a cartilage bone. This willrequire further investigation. The paired bone in thejuvenile developed into large single bone in the adult,still maintaining its distal location in the penile tis-sue and so indicating a similar function in the adultand in the juvenile. This may be to support erectionfor micturition and not necessarily for intromission.REFERENCES1. Beresford WA, Burkart S (1977) The penile bone andanterior process of the rat in scanning electron mi-croscopy. J Anat, 124: 589597.2. Bolton LA, Camby D, Boomker J (1996) Aberrant mi-gration of ancylostoma caninum to the os penis of adog. J S Afr Vet Assoc, 67: 161162.3. Cunha GR, Lung B (1978) The possible influence oftemporal factors in androgenic responsiveness of uro-genital tissue recombinants from wild-type androgen-sensitive mice. J Exp Zool, 205: 181194.4. Fairon J (1980) 2nd New chiroptera for fauna of the airmountain massif (Niger); otonycteris hemprichi andpippestrellus nanus. J Bull Instr Sci Nat Belg Biol, 52:17.5. Glucksmann A, Cherry CP (1972) The hormonal induc-tion of an os clitoridis in neonatal and adult rat. J Anat,112: 223231.6. Hamilton WJ, Boyd D (1976) A textbook of human anat-omy. Oxford University Press, UK.7. Iguchi T, Irisawa S, Uesugi Y, Kusunoki S, Takasugi N(1990) Abnormal development of the os penis in malemice treated neonatally with tamoxifen. Acta Anat(Basel), 139: 201208.8. Krutzsch PH, Crichton EG (1987) Reproductive biologyof the male mastiff bat, mormopterus planiceps (Chi-roptera: Molossidae), in Southeast Australia. Am J Anat,178: 352368.9. Krutzsch PH, Watson RH, Lox CD (1976) Reproductivebiology of the male leaf-nosed bat, macrotus waterhousiiin southern united states. Anat Rec, 184: 611635.10. McGee-Russell SM (1958) Histochemical methods forcalcium. J Histohem, 6: 2242.11. Murakami R, Mizuno T (1984) Histogenesis of the ospenis and os clitoridis in rats. Dev Growth Differ, 26:419426.12. Murakami R, Mizuno T (1986) Proximo-distal sequenceof development of the skeletal tissues in the penis ofrat and the indicative effect of epithelium. J EmbryolExp Morphol, 92: 133143.13. Onodera S, Shigehara N, Eto M (1987) Discriminant anal-ysis of the sexual differences of the skeletons in shibadog (Canis familiaris). Acta Anat Nippon, 62: 3132.14. Rasmussen KK, Vilmann H, Juhl M (1986) Os penis ofthe rat. V. The distal cartilage process. Acta Anat (Basel)125: 208212.15. Vilmann H (1982) Os penis of the rat. Iii. Formationand growth of the bone. Acta Morphol Neerl Scand,20: 309318.Figure 2. Photograph of penis of adult Eidolon helvum (180 g).The penis has a larger distal portion and a narrow proximal por-tion. The os penis is located at the distal portion (arrow). Stain-ing with Alizarin red S. 500 x156Folia Morphol., 2000, Vol. 59, No. 316. Vilmann H (1991) Os penis of the rat. VI. Scanningelectron microscopy of the surfaces of the maturebone. Anat Anz, 167172.17. Vilmann H, Vilmann A (1979) Os penis of the rat. II. Mor-phology of the mature bone. Anat Anz, 146: 483493.18. Williams-Ashman HG, Reddi AH (1991) Differentiationof mesenchymal tissues during phalic morphogenesiswith emphasis on the os penis: Roles of Androgensand Other Regulatory Agents. J Steroid Biochem MolBiol, 39: 873881.

The os penis of the frugivorous bat Eidolon helvum (Kerr)

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The os penis of the frugivorous bat Eidolon helvum (Kerr)

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