tail of epididymis.
Ductus Deferens
The ductus deferens is attached to the medial side of the testicle by the mesoductus [5]. The ductus deferens is the continuation of the tail of the epididymis (Figure 1.6). The ductus deferens enters the abdominal cavity through the inguinal canal, crosses the lateral ligament of the bladder, and before ending at the colliculus seminalis in the urethra widens into the ampulla [5].
Figure 1.6 Components of epididymis: Sc = spermatic cord, Ep‐h = head of epididymis, Ep‐b = body of epididymis, Ep‐t = tail of epididymis, Dd = ductus deferens.
Transfer
The transfer of spermatozoa from the bull to the cow is achieved by the process of intromission, which requires erection of the penis and ejaculation of sperm. The pertinent anatomy for these processes to occur includes the penis, the musculature of the penis, the vasculature, and the innervations.
Penis
The penis of the bull can be divided into a root, body, and glans penis (Figure 1.7). The root of the penis can be defined as the origin of the erectile tissue that comprises the penis as well as the origin of the muscles of the penis. The erectile tissue that makes up the bulk of the penis is the corpus cavernosum. The paired corpora cavernosa originate separately on each side of the ischiatic arch medial to the ischiatic tuberosity. These individual limbs are termed the crura of the penis. The crura pass ventromedially until they join to form the body of the penis. The corpus spongiosum is the erectile tissue that surrounds the urethra. The origin of the corpus spongiosum, called the bulb of the penis, originates between the crura along the midline of the ischiatic arch. Therefore the root of the penis is composed of the crura (corpus cavernosum) and the bulb (corpus spongiosum).
Figure 1.7 Regions of the penis: R = root of penis, Bb = bulb of penis, Bd = body of penis, Fp = free part of penis, G = glans penis.
The erectile tissue is enclosed in the dense outer covering of the tunica albuginea. The tunica albuginea is a dense covering that consists of an inner circular layer and outer longitudinal layer of fibers. The inner circular layer sends trabecular scaffolds throughout the corpus cavernosum for the attachment of the cavernous endothelium.
Located caudal to the root of the penis are the muscles of the penis: the ischiocavernosus, bulbospongiosus, and retractor penis muscles (Figure 1.8). The paired ischiocavernosus muscles originate on the medial surfaces of the ischiatic tuberosities overlying the crura; the muscle fibers pass ventromedially in a “V” fashion until ending a short distance on the body of the penis [1]. During erection the ischiocavernosus muscle contracts, pushing blood from the cavernous spaces of the crura into the body of the penis [7]. The bulbospongiosus muscle lies caudal to the bulb of the penis, originating along the ischiatic arch and continuing until the junction of the crura [1]. The bulbospongiosus muscle fibers run transversely across the bulb of the penis and contraction of this muscle results in propulsion of the ejaculate through the urethra [7]. The retractor penis muscle extends from the caudal vertebrae and internal anal sphincter to insert distal to the sigmoid flexure [8]. These paired muscles relax during erection, allowing the penis to extend from the prepuce and contract during quiescence, retracting the penis into the sheath [8].
Figure 1.8 Muscles of the penis: Bs = bulbospongiosus muscle, Ic = ischiocavernosus muscle, Rp = retractor penis muscle.
The body of the penis begins where the two crura meet distally to the ischiatic arch; it extends craniad, along the ventral body wall to become at the mid‐ventral abdomen the free part of the penis (Figure 1.9). The body of the penis is bent in an “S” shape called the sigmoid flexure. The proximal bend of the sigmoid flexure opens caudally and is located near the scrotum. The distal bend is opened cranially and the short suspensory ligaments of the penis attach the penis to the ventral surface of the ischiatic arch. The glans penis is a small restricted region at the tip of the free part of the penis [8] (Figure 1.10). The free part of the penis is the distal extent from the attachment of the internal lamina of the prepuce to the glans penis [8]. The free end of the penis is twisted in a counterclockwise direction as viewed from the right side, illustrated by the oblique direction of the raphe of prepuce continued as the raphe of the penis to the urethral process (Figure 1.11). The twist of the free end of the penis is due to the attachment of the apical ligament. The apical ligament of the penis is formed by the longitudinal fibers of the tunica albuginea leaving the body of the penis just distal to the sigmoid flexure and reattaching near the apex of the penis [9].
Figure 1.9 Sigmoid flexure of the penis: Bd = body of penis, Sf = sigmoid flexure.
Figure 1.10 Glans penis and associated structures: G = glans penis, Fp = free part, Ip = internal lamina of prepuce.
Figure 1.11 Prepuce and associated structures: Rp = raphe of penis, Ip = internal lamina of prepuce, G = glans penis, Up = urethral process.
The prepuce of the penis is composed of an external and internal fold or lamina [8] (Figure 1.12). The external lamina is the haired outer fold of skin attached to the ventral abdomen. The haired skin terminates at the preputial orifice where the external fold turns inward to line the preputial cavity as the internal lamina. The internal lamina serves to attach the external lamina to the penile epithelium.
Figure 1.12 Components of the prepuce: Fp = free part of penis, G = glans penis, Ip = internal lamina of prepuce, Ep = external lamina of prepuce, Po = preputial orifice.
Blood Supply
Before ejaculation can occur the testis must produce spermatozoa. This requires an adequate blood supply for the metabolic demands of cellular division for