Anatomy of the External Genitalia

The anatomy of the male reproductive organs has been thoroughly investigated by several authors in the dromedary.^{(6, 15, 21, 22, 40, 44, 60-62, 69, 79)} in the llama and alpaca,^{(13, 16, 18, 30, 47, 64)} in guanaco and vicuña ^{(17, 76, 77)} and in the Bactrian camel.⁽¹²⁾

The scrotum and testis

General description and position

The scrotum is located in the perineal region in camelidae with the testicles directed caudo-dorsally ^{(4, 30, 40, 64, 69, 70)} in the dromedary, it is situated 4 to 6 cm below the anus. It is a relatively thick-walled structure with different elasticity, depending on the season and sexual activity. The scrotal skin is smooth and fine during the peak of the breeding season and becomes thick and rugose during the period of sexual rest because of decreased testicular size and increased folding of the skin. The neck of the scrotum is short compared to other species but increases in length in older animals. The general form of each scrotal sac is ovoid (Figure 1.1).^{(4, 69)} In the South American camelidae, the scrotum is similarly small, not pendulous (small neck) and situated high in the perineal region at the level of the ischial arch (Figure 1.2).^{(9, 30)} No seasonal variation of the scrotum has been described in llamas and alpacas. However, in the vicuña, testicular size was greater in summer than in winter.⁽⁷⁶⁾

Detailed description of the anatomy of the scrotum in the Bactrian camel is lacking. Our observations on a few males suggest that it is very similar to that of the dromedary but less pendulous.

Development and embryogenesis

Little is known about the embryonic development of the male genitalia and testicular descent in camelidae. In one study on dromedary fetuses, all testicular structures were differentiated and easily identifiable in 8-9 month fetuses. The epithelial cords are clearly visible and consist mainly of undifferentiated cells and few primordial sex cells. They are surrounded by fine connective tissue layers continuous with the connective tissue of the mediastinum testis. At 9 to 10 months of pregnancy, the fetal testicle offers a histological organization similar to that of the adult animal with well-differentiated interstitial tissue, seminiferous tubules and rete testis. The tunica albuginea is well differentiated and richly vascularized and projects into the testicular parenchyma to form septae containing the germinal cords (seminiferous tubules). The fetal seminiferous tubules are surrounded by a capsule of connective tissue and a well-defined basement membrane and present two types of cells: primordial germ cells (spermatogonia) and support cells (Sertoli cells).⁽²⁶⁾

The mechanism and chronology of testicular descent remains unstudied in the camelidae. At 7 months, the testicles lie caudal to the superficial inguinal ring. According to some authors, testicular descent is not complete until the second or third year of life in the dromedary and Bactrian camels (Figure 1.3).⁽⁶⁵⁾ In the llama and alpaca, the testes are already present in the scrotum at birth, but they are usually soft and difficult to palpate.^{(30, 64, 67)}

Size and weight of the testis

Testicular size is an important parameter in the evaluation of the breeding potential of males and can be used to predict daily sperm production because of the high correlation found between scrotal measurements, testicular weight and total sperm production (cf. Physiology).⁽⁴⁾
 

In the dromedary camel, reported testicular dimensions vary from one author to another. This variation is probably due to the effect of age, sexual activity and even the "breed" or strain studied. The long axis and diameter of the testes range respectively from 6 to 13 cm and 3 to 6 cm for dromedaries in India.⁽⁶²⁾ Somewhat smaller values were reported for dromedaries in Egypt.⁽⁶⁹⁾ The mean testicular length and width are respectively 9.3 ± 0.71 cm and 4.5 ± 0.41 cm in the rainy season and 9.5 ± 0.61 cm and 4.5 ± 0.51 cm in the dry seasons in Nigeria.⁽¹⁹⁾ The mean scrotal circumference reported for 197 dromedaries was 32'.4 ± 2.41 cm and was positively correlated with age.⁽¹⁹⁾ As a general rule, the average testicular length, width, and depth are 9.1, 5.1 and 4.3 cm and the average weight is 92 g for male dromedaries 3 years and older.

The wide range of the mean testicular weight values reported by different authors (66 to 93 g⁽⁷⁸⁾; 80 to 110 g⁽⁶⁹⁾; 32 to 225 g⁽⁶²⁾; 57.1 to 109.2 g⁽⁷⁵⁾) suggest that the type of dromedaries and season have a significant effect on testicular size.

Most studies report a significant effect of season on testicular weight in the dromedary with the largest recorded values during the breeding season (usually the coolest months of the year) and the lowest values recorded outside the breeding season (during the hottest months of the year).^{(62, 69, 75, 79)} In Nigeria, the effect of seson is not very clear as testicular weight was respectively 36.7 ± 0.9 g and 37.6 ± 0.8 g for the rainy and dry seasons.⁽¹⁹⁾ In a study in India⁽⁶²⁾ the effect of season on the weight of the testicle was more pronounced in dromedaries between 9 and 14 years of age than in dromedaries younger than 9 or older than 14. The maximum weight of the left testicle was observed during the period of December through March (36 to 225 g) compared to April to July (32 to 181 g) and the period of August to November (32 to 191 g). Season also has a marked effect on the consistency of the testis. During the breeding season, dromedary testicles are usually turgid and become soft during the period of sexual rest.⁽⁶²⁾
 

Usually one testis has a slightly higher position than the other and the right testicle is usually smaller than the left one.^{(1, 2, 21, 22, 62)} This difference of size between the testes is observed across seasons and age groups (Table l).⁽⁶²⁾

In South American camelidae, the testicles are relatively small compared to those of other species. They are ovoid and present a great variation in size. In yearlings, the testes measure on average 1.1 to 1.4 cm in length.⁽⁶⁴⁾ In adult llamas, the length, width and depth are respectively 5-7 cm, 2.5-3.5 cm and 3-4 cm.^{(30- 64)} In the alpaca, the length and width of the testis are 4 to 5 cm and 2.5 to 3 cm respectively.⁽⁶⁴⁾ In the vicuña, longitudinal and transverse testicular diameters are respectively 3.3 cm and 1.69 cm in February (summer) and 2.64 cm and 1.50 in August (winter).⁽⁷⁷⁾ The average individual testicular weight recorded in 3.5-year-old llamas (average body weight of 133 kg) is 24 g.⁽³⁸⁾ The effect of season on the size and weight of the testis does not seem to be an issue in domesticated South American camelidae as is the case in the dromedary, the Bactrian camel and the vicuña.

Testicular envelopes

Testicular envelopes in the dromedary are similar to those described for other species (Figure 1.4). The tunica albuginea is closely adhered to the testis and gives off trabuculae or septae which divide the testicular parenchyma into several lobules.^{(62, 69)} The septae converge centrally to merge with the mediastinum (rete testis).

Testicular parenchyma appears orange pink in the young animal and becomes darker in older males (Figure 1.5).
 

Histology

The camelidae testis has a general histological organization similar to that of most species (llama; ^{10, 11, 17, 18,  28, 31, 55, 58)} dromedary^{(1, 3, 23, 32, 48-50, 54, 60-63, 73. 75)}) The testicular parenchyma is composed of two compartments: the interstitial tissue and the seminiferous tubule, contained in a tunica albuginea (Figure 1.6).

Tunica

The dromedary testis is covered by a 500-3900 µm thick tunica albuginea.^{(61, 62, 69)} This tunica is characterized by the presence of isolated bundles of smooth fibers and a rich vascular supply (Figure 1.7).^{(61, 62)}

Interstitial tissue

The interstitial tissue in the dromedary testis is composed mainly of Leydig cells and connective tissue with vascular supply (Figure 1.6).^{(61, 62, 78)} The interstitial tissue occupies a larger area than the seminiferous tubules, particularly during the winter months and seems to be the major factor in the seasonal variation of testicular size and weight.⁽⁷⁵⁾ The increased amount of interstitial tissue observed during the breeding season is due to an increase in the number and volume of Leydig cells.^{(61, 62)} Leydig cells present a large nucleus situated in an eccentric position. This tissue tends to become reddish brown with advanced age due to the increased amount of lipoid pigments in the cytoplasm of Leydig cells in the dromedaries which emit a reddish-orange fluorescence under ultraviolet light.

Seminiferous tubules

The outer diameter of the seminiferous tubules in adult dromedaries varies according to studies and was found to be in the range of 131-183 µm,⁽⁷⁸⁾ 180-215 µm.⁽¹⁾ 113-250 µm ⁽⁶¹⁾ and 152-202 µm.⁽⁷⁵⁾ This variability could reflect an effect of the type of dromedaries studied and/or the effect of age and season.

The diameter of the seminiferous tubules is greatest during the breeding season (at the end of the winter), decreases continuously from the end of winter until mid-summer, then starts to increase in fall.^{(1, 75)}

The seminiferous tubule of the dromedary is structured in the same manner as that of other domestic animal species, with a boundary tissue containing germinal (spermatogonia) and support cells (Sertoli cells) (Figure 1.8). The ultrastructure of the seminiferous tubule of the dromedary shows that the boundary tissue consists of three lamellae: inner fibrous, inner cellular and outer cellular. The inner lamella is subdivided into two homogeneous layers enclosing a third one that contains collageneous fibers and fine filaments. The inner cellular lamella consists of several layers of myoid cells; each layer is separated from the adjacent layer by homogenous material and varying amounts of collagen. The outer cellular lamella consists predominantly of fibrocytes together with some fibroblast and scattered collagen.⁽⁴⁵⁾
 

Some early reports indicated a complete arrest of spermatogenic activity during the summer season.⁽⁷⁸⁾ However, in later studies, it was found that spermatogenesis in the dromedary is present all year round.⁽⁶¹⁾ It is possible that the effect of season on spermatogenesis varies from one geographical location to another (cf. Spermatogenesis, physiology).

The seminiferous tubules end with a terminal segment which presents histological features that are different from the rest of the tubule.^{(50, 61, 62)} As the seminiferous tubule nears the terminal segment it becomes tapered and the germ cells are gradually lost leaving a simple columnar epithelium formed by modified Sertoli cells.^{(50, 52, 63)} A detailed account of the ultrastructure of the epithelium of the terminal segment of the seminiferous tubule in the dromedary and its relationship to its function was given by Osman and Ploen.⁽⁵²⁾ It was found that the modified Sertoli cells form a plug-like structure inside the receptacle. These cells vary in height and present a straight interdigitated basal border, vacuolated apical cytoplasm and a few short microvilli on its luminal border. The cytoplasm of the modified Sertoli cells generally contains a large, irregular nucleus and a distinct non-vacuolated free nucleolus.^(50-51) The cytoplasm also presents many vacuoles and a moderate number of mitochondria, microtubules and microfilaments, dense bodies, and residual bodies. These cells also show an abundant rough endoplasmic reticulum (RER) but a small Golgi apparatus and smooth endoplasmic reticulum (SER). These ultrastructural characteristics, as well as the presence of spermatozoa at different stages of degradation within the modified Sertoli cells, suggest that the epithelium of the terminal segment of the seminiferous tubule plays an active role in the modification and regulation of the seminiferous tubule fluid and the removal of "unwanted" spermatozoa.⁽⁵⁰⁾

Rete testis

The rete testis occupies a centrally located mediastinum and is in the form of irregular and anastomosing channels. Its epithelium varies from simple squamous, simple cuboidal, to simple columnar with a few basal cells. Areas similar to the distal part of the tubulus rectus are also seen at the periphery of the rete testis.⁽⁴⁸⁾

The ultrastructure of the cells of the rete testis is similar to that in the tubulus rectus. Some cells show an increased amount of glycogen, mostly in the supranuclear region. Phagocytic elimination of spermatozoa by the epithelium of the rete testis has been demonstrated. Other cell types (macrophages and lymphocytes) are also found in the lumen of the tubulus rectus.⁽⁴⁸⁾

Tubuli recti

The tubuli recti (straight tubules) represent the end part of the seminiferous tubule where the convoluted morphology is lost and the tubule becomes straight. The tubuli recti connect the seminiferous tubule to the rete testis. Singh and Bharadwaj⁽⁶³⁾ divided this segment in the dromedary into three portions: the receptacle, the narrow main part and the wider distal part.

The receptacle has a wide lumen and is lined with a simple squamous or low cuboidal epithelium. The epithelial cells of the receptacle have oval nuclei with their long axes parallel to the basal lamina.⁽⁴⁸⁾

The main part has a narrow lumen and is mostly lined by a single layer of cuboidal cells with a few areas of columnar cells. The nuclei of these cells are either round or oval in shape. The distal part has a wide lumen and is lined by a simple cuboidal or simple columnar epthelium with a few basal cells. The epithelium contains numerous macrophages and lymphocytes. Based on the ultrastructural and histochemical studies of the tubulus rectus, it was suggested that this segment of the intratesticular seminal pathway is involved in modification of the testicular fluid secreted inside the seminiferous tubules, and elimination by phagocytosis of dead or abnormal spermatozoa.^(48, 50)

Vascular supply

Blood is supplied to the testicle primarily via the testicular artery. The testicular artery originates on both the right and left sides, from the aorta just cranial to its bifurcation, near the origin of the posterior mesenteric artery. It starts small in diameter and runs straight towards the deep inguinal ring where it becomes embedded in the vascular fold of the tunica vaginalis. The artery becomes convoluted as it reaches the superficial inguinal ring, enters the testicular cord and approaches the pampiniform plexus where it becomes coiled (Figure 1.9). The average length of the artery ranges from 280 to 390 cm, most of which is confined to a small area because of its extensive coiling.^{(53, 60, 61, 65)} Along its trajectory, the testicular artery gives off several branches that will supply blood successively to the testicular cord envelopes, the epididymis and the testicular parenchyma.

A detailed description of the trajectory of the testicular artery was given by Osman et al.⁽⁵³⁾ The most distinct features of the artery during its trajectory are its enlargement as it approaches the testis and the distribution of its branches. The artery runs superficially along the attached border, becomes subalbuginal and then runs deep into the parenchyma in the caudal extremity of the testis. The testicular artery resurfaces under the cauda epididymis then curves downwards before it continues cranially around the extremity of the testis and divides into 2 to 4 large branches on the the free border giving off smaller convoluted branches to the lateral and medial surfaces of the testis. The small convuluted branches divide into even smaller branches that run through the testicular septa and supply blood to the testicular parenchyma.⁽⁵³⁾

The epididymal branch arises from the upper part of the the pampiniform plexus and runs along the body of the epididymis which it supplies then divides into several branches at the level of the cauda epididymis, which anastomose with the deferential artery (artery of ductus deferens).⁽⁵³⁾ The head of the epididymis is supplied by branches of the testicular artery given off at the level of the pampiniform plexus.⁽⁶²⁾

The epididymis

Morphology

Like in other species, the epididymis is composed of three distinct parts: the caput (head), corpus (body) and cauda (tail). The epididymis faces laterally and is located along the dorsal border of the testis with the head curving around the cranial pole of the testis (Figure 1.10). The epididymis adheres to the cranial surface and both extremities of the testis, allowing the corpus epididymis to form a sinus with the testis situated externally.

In the dromedary, the cauda epididymidis is round and well-protruded about 3-4 cm above the respective extremity of the testis. It is attached to the testis by the proper ligament. The total weight of the epididymis is approximately 10-40 g, and the weight ratio between the testis and the epididymis varies from 3:1 to 6:1.⁽⁶²⁾

In llamas, the epididymis is also closely attached to the testis; all 3 parts can be palpated.^{(9, 30)}

Histology

The epididymis is connected to the rete testis by several ductuli efferentes which originate from the sac in the dromedary testis and do not emerge directly from the rete testis as previously suggested.⁽⁶³⁾

The rete testis and the sac in the dromedary are lined by simple cuboidal non-ciliated cells.⁽⁶³⁾ The epithelium of the ductuli efferentes in the dromedary is similar to that of other species and comprises simple high columnar ciliated cells alternating with low columnar non-ciliated cells. The most important peculiarity of the histology of the ductus efferentes in the dromedary is the presence of a circular layer of smooth muscle fibers surrounding it.⁽⁶³⁾ The presence of intraepithelial glands in the head and body regions of the epididymis has been reported in the dromedary.⁽⁶³⁾ The isolated bundles of smooth muscle fibers in the capsule of the cauda epididymidis in the dromedary are similar in location to those described in the horse.
 

The dromedary epididymis is divided, on the basis of histological appearance, into three segments: initial, middle and terminal (Figure 1.11). The middle segment is further divided into proximal, intermediate and distal parts. The initial segment is characterized by a regular, smooth contour and a wide lumen (200 µm) containing few spermatozoa. The epithelial lining consists of typical pseudostratified ciliated columnar cells, and average height is about 130 µm on a distinct basal lamina.⁽⁶³⁾

The proximal part of the middle segment is small and characterized by a slight reduction in the diameter of the lumen (180 µm) with sparse sperm content (Figure 1.12). The epithelial lining of this segment is smaller (85 µm) with ciliated cells containing different-sized cytoplasmic vacuoles. The height of the epithelium (70 µm) of the epididymis becomes somewhat smaller in the intermediate part of the middle segment, and the lumen (160 µm) is packed with spermatozoa (Figure 1.13). The distal part of the middle segment is the longest and extends over most of what is classically described as the corpus epididymidis. The epithelial cells as well as their ciliated border are smaller in height and present a highly vacuolated cytoplasm. The lumen contains spermatozoa but no dense masses are observed.⁽⁶³⁾ The terminal segment of the epididymis which continues into the ductus deferens has a wider lumen (450 µm) packed with spermatozoa, but the ciliated border of the epithelial lining is considerable shorter (5 µm) (Figure 1.14).⁽⁷²⁾

In the llama, the epididymis is divided into 6 segments according to histological and histochemical criteria (Figure 1.15).⁽¹⁶⁾

These regional differences represent different secretory functions that may play a role in the process of sperm maturation (cf. Physiology). Segment 1 represents a short region where ductuli efferentes enter the epididymal duct. Segments II and III are characterized by a high epithelium and mitotic activity and weak LDH activity. Epithelial cells in segment IV contain PAS-positive, amylase and neuraminidase-resistant secretory granules. Segment V is characterized by a strong acid phosphatase and lactate dehydrogenase activities. Segment VI is characterized by moderate acid phosphatase and high lactate dehydrogenase activities and is highly packed with spem cells.⁽¹⁶⁾
 

Ductus Deferens

In the dromedary, the ductus deferens leaves the cauda epididymidis at its medial aspect and runs cranially along with the testicular blood vessels to form the funiculus spermaticus. The ductus deferens is very long. It enters the abdominal cavity via the medial angle of the inguinal canal then turns caudally in the genital fold, becomes straight and thick forming the ampulla which passes deep into the prostate and opens directly into the colliculus seminalis via an ostium ejaculatorium (ejaculatory orifice).^{(21, 65)} The histology of the ductus deferens resembles that of the terminal part of the eipididymis (Figure 1.16).

In the llama, the ductus deferens is 1 mm in diameter at the junction of the epididymis. It widens to 2 mm in the abdominal cavity toward the pelvic urethra. The length of the ductus deferens is about 40 cm.⁽⁶⁴⁾
 

The prepuce and penis

Prepuce

Position and conformation

The dromedary prepuce is located in the inguinal region. It is flattened from side to side and triangular in shape when viewed laterally. In the absence of sexual arousal, the small preputial orifice (Ostium praeputiale) is directed caudally.^(19,44) The preputial skin is usually darker in color than the rest of the body. It is covered with short fine hair and presents two black nipples on either side of the base of the prepuce, near its caudal border. In males that are used intensively for breeding, a callus may develop at the lower part of the cranial curvature (Figure 1.17).

The average length of the base, cranial and caudal borders is 28.0, 17.5 and 19.7 cm, respectively.⁽⁴⁴⁾ The prepuce of the dromedary is formed from a single parietal layer which is reflected on the penis to form the visceral or penile layer. The parietal and penile layers of the prepuce are brown or dark gray in color. The preputial orifice (Ostium preputiale) is narrow (external diameter 1.5 to 2.5 cm).^{(44, 65)} The penis is attached at birth to the prepuce and does not become free until 2 to 3 years of age.

The conformation and situation of the prepuce in llamas and alpacas is similar to that of the dromedary.^{(30, 38)} In these species the prepuce is adherent to the glans penis until 2 or 3 years of age making exteriorization of the penis impossible before this age.⁽³⁰⁾

Musculature

The dromedary prepuce has a well-developed musculature which permits the movements of the prepucial orifice needed for changing its direction during erection and marking behavior. These muscles are identified as the cranial prepucial muscle, the lateral prepucial muscle, and the caudal prepucial muscle. The cranial preputial muscle (M. Praeputialis cranialis) is the largest. It originates from the deep fascia of the ventral abdominal wall with the most medial fibers originating from the linea alba, just cranial to the umbilicus.⁽⁴⁴⁾ The muscle fibers pass caudo-medial to be inserted into the cranial part of the prepuce. This muscle is responsible for directing the prepucial orifice forward during copulation. The lateral preputial muscle originates from the deep fascia of the abdomen and is inserted into the inner aspect of the lateral part of the prepuce. It is the weakest of the 3 muscles - thus the limited lateral movements of the dromedary prepuce. The caudal preputial muscle (M. praeputialis caudalis) is composed of one lateral and 2 middle groups of fibers. The lateral fibers originate in the deep fascia of the abdomen medial to the superficial inguinal lymph nodes, while the middle ones come from a fascia which is continuous with that of the thigh. The medial bundles are very weak and are attached to the fascia of the penis. The 3 preputial muscles are inserted into the inner surface of the skin covering of the free part of the penis.⁽⁴⁴⁾ Similar preputial muscles are described for llamas.⁽³⁰⁾
 

Penis

The type of penis determines the mechanisms of erection as well as the copulatory behavior of a species. Thus, the study of the anatomy of the penis is of utmost importance in order to comprehend these mechanisms.^{(40, 43, 69, 70)}

Conformation

The penis of camelidae is of the fibroelastic type and relies primarily on its elasticity for erection and extension. In the absence of erection, the penis is retracted into its sheath via a prescrotal sigmoid flexure (Flexura sigmoidea penis) (Figures 1.18 and 1.19).^{(19, 30, 38, 44, 64)}

The length of the penis ranges from 59 to 68 cm in the dromedary)^{(19, 44)} and 35 to 40 cm in llamas and alpacas.^{(9,  30, 38, 64)} Camelidae penis is cylindrical, gradually decreasing in diameter from its root (ischial arch) (2.2 cm in the dromedary, 1.2 to 2 cm in the llama) to the neck of the glans penis (collum glandis, prepucial reflexion) (0.4 cm in the dromedary, 0.8 to 1 cm in the llama) (Figure 1.20, 1.21).^{(30, 44)}

The penis originates in the region of the ischiatic arch through three cavernous bodies by a thick tunica albuginea.⁽¹⁹⁾It is divided into 3 segments; the root of the penis, the body of the penis, the free end of the penis and the glans penis.

The root of the penis is dorso-ventrally flattened and its cross-section has an elliptical shape. It is enclosed by 2 dorsal and 2 ventral ischiocavemosus muscles. Two Crura penis covered by the ischiocavernous muscle form the attachement of the organ to the ischial arch (Figure 1.22). Section of the penis shows three cavernous bodies, two on the dorsal aspect (Corpora cavernosa penis) and the third on the ventral aspect (Corpus cavemosum urethrae) surrounded by a thick tunica albuginea penis (5-7 mm) which forms an indistinct urethral groove (Sulcus urethralis). The urethral cavernous tissue is circular and covers the urethra ventrally and laterally. At this level of the penis, the septum penis is fairly thick (8-9 mm) and well identified (Figure 1.20a,b,c).^{(44, 65)}

The body of the penis (corpus penis) is generally subdivided into 3 segments: the caudal third, the middle portion and the cranial third. The major differences amongst these parts is the diminution of the transverse diameter and the reduction of the cavernous system and its replacement by a fibrous tissue from the caudal part to the cranial part. The cross section of the penile body at the level of the caudal portion is almost elliptical and shows flat dorsal and ventral surfaces (Figure 1.20e). In this part the fibrous architecture of the penis increases to replace most of the cavernous structure of the penile body.⁽⁴⁴⁾

The transverse section of the free end of the penis is elliptical in its caudal half but ovoid in the cranial one. This region of the penis is characterized by an increase in the cavernous structure of the corpus cavemosum penis which replaces the fibrous trabeculae. The septum penis becomes indistinguishable (Figure 1.20g,h). Two large blood spaces are usually present in the dorsal third on either side of the middle line of the penis. The urethra is surrounded by large blood spaces corresponding to the corpus cavemosum urethrae. In this part of the penis the urethra changes from a central position to become more lateral and to the left.⁽⁴⁴⁾

The Glans penis is cartilaginous, twisted like a hook and curved along its vertical plane which is convex on the right and cranial aspects and concave on the left and caudal ones (Figure 1.21). The glans penis shows a marked constriction (neck or Collum glandis). Its length, measured along its dorso-cranial convexity, averages 2.6 cm.⁽¹⁹⁾ In cross-section, it presents a concentric ring of hyaline cartilage with centrally placed blood vessels. Many elastic fibers and caverns are found outside the ring of cartilage.^{(44, 69)} A small urethral process (Processus urethrae) is present on the lateral aspect to the external urethral orifice on the left side of the glans penis.^{(44, 65)}

The anatomy of the penis of the South American camelidae resembles that of the dromedary. The glans penis is long (9-12 cm) and presents a cartilaginous process that has a slight clockwise curvature.^{(9, 30)} The end of the urethra is not located at the tip of the penis but rather at the base of the cartilaginous process.⁽⁹⁾ These anatomical features (curved cartilaginous process) of the camelidae penis allows penetration of the cervical rings, through combined rotational and thrusting movement, followed by intrauterine deposition of semen.
 

Musculature

The major group of muscles in the dromedary penis is located on its root and consists of two dorsal and two ventral ischiocavemosus muscles (M. ischiocavemosus).The dorsal muscles originate in the ischiatic tuber and are inserted into the lateral aspect of the root of the penis, just at the level of the ischial arch.^{(44, 65)} The ventral ischiocavernous muscles are provided with a tendinous origin from the ischiatic tuber and the fascia covering the retroperitoneal part of the ventral aspect of the rectum. They are inserted mainly into the ventral aspect of the root of the penis, 3-5 cm caudal to the ischial arch (Figure 1.22).⁽⁴⁴⁾

The retractor penis muscles (M retractor penis) which originate from the transverse processes of the first and second coccygeal vertebrae pass around the anus to come in contact with each other below, forming the rectal part of the retractor penis muscle. These muscles continue on the ventral aspect of the penis and are attached to the ventral convexity of the sigmoid flexure of the penis, 3-4 cm from the preputial fornix (Figure 1.22).

Vascular supply

Blood is supplied to the penis by the penile artery which is the continuation of the internal pudendal artery (Figure 1.23). This artery divides into 3 vessels at the level of the ischial arch: the A. bulbi penis which supplies the bulb of the penis, the deep penile artery which supplies the crus penis, and the caudal scrotal branch (R. scrotalis caudalis) which supplies the scrotum.⁽⁶⁵⁾

Although the angioarchitecture of the penis of the dromedary is abundant at its root and free extremity, the body is formed mainly of fibrous trabeculae. The cavernous characteristic of the corpus cavemosum urethrae at the root of the penis is replaced in its body and free end by large blood spaces.⁽⁴⁴⁾

The study of the micromorpholgy of the arteries of dromedary penis shows valve-like arterial polsters in the collateral branches of A. profunda penis which may have a significance in the regulation of blood flowto the organ.⁽⁴⁴⁾

References

1.    Abdel-Raouf, M„ M. R. F. El-Bab. and M. M. Owaida. 1975. Studies on Reproduction in the Camel (Camelus dromedarius) V. Morphology of the Testis in Relation to Age and Season. J. Reprod. Fert. 43:109-116.
2.    Abdel-Raouf, M., and M. M. Owaida. 1974. Studies on reproduction in camels. IV. Gross changes in the morphology of the testis in relation to age and season. Assuit Vet. Med. J. 1:215-223.
3.    Abou-Ahmed, M. M„ A. A. Seida. A. M. Ghallab, S. T. Ismail, and A. B. Elwishy. 1988. Effects of Age and Season on Weight and Some Biochemical Attributes of the Accessory Genital Glands of the One-humped Male Camel (Camelus dromedarius). Zuchthyg. 23:26-32.
4.    Akingbemi, B. T., and T. A. Aire. 1991. Testicular dimensions in sperm reserves in the camel (Camelus dromedarius) in Nigeria. Bull. Anim. Hlth. Prod. Afr. 39:121-123.
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