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After dissecting the tail, perineum, prepuce and penis (also the inguinal region if the specimen given is a female) the hind limb is separated from the body by cutting through the pelvic symphysis and the lumbo-sacral spine on the median line so that the dissector will have a part of the abdominal wall in front of the pubis for examination.
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If the subject is a male, the penis and also one testicle in its scrotal bag are left intact with one of the limbs.
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Medial aspect of the hip is ready for inspection.
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Clean the fascia and peritoneum covering the blood vessels and nerves on the pelvic wall only. Do not distrub the peritoneum elsewhere.
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Abdominal aorta: It runs under the bodies of lumbar vertebrae and terminates by dividing into two internal iliac arteries under the body of the fifth lumbar vertebra. The two lateral branches from aorta in front of the internal iliacs are the external iliac arteries to supply the limbs. The internal iliac arteries supply the pelvic walls, pelvic organs, hind limb and the external genitalia. Half of the aorta will be found under the lumbar vertebrae.
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Posterior vena cava: It is a large venous trunk draining the venous blood from the hind limbs, pelvic organs, abdominal walls, kidneys and liver. It is found to the right of the abdominal aorta under the bodies of the lumbar vertebrae. It is formed by the union of the two common iliac veins above and to the right of the origin of the iliac arteries. Half the section of the vena cava may be found with each limb.
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Internal iliac artery: It passes obliquely downward and backward across the upper part of the sacro-sciatic ligament in company with the satellite vein and terminates at the lesser sciatic foramen by dividing into the posterior gluteal and internal pudic arteries.
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Its collateral branches are:
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A large common trunk after giving a branch to ureter divides into the umbilical and vesical arteries in the male. The umbilical artery functions only in the foetus and gets fibrosed into a rounded cord the round ligament of the bladder when the young one is born. The vesical artery supplies the body and the horn of the uterus.
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A short common trunk which divides into (a) sixth lumbar artery which goes up to the dorsal aspect of the spine, (b) lateral sacral artery (if the middle sacral artery is absent) takes of the place of middle sacral artery, runs under sacrum and is continued as middle coccygeal artery under the coccygeal vertebrae, (c) anterior gluteal artery which passes through the greater sciatic foramen to supply the gluteal muscles.
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Vesicogenital artery supplies bladder, ureter, ductus deferens, vesiculae seminalis, prostate and urethra.
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The posterior gluteal artery passes out of the pelvic cavity through the lessor sciatic foramen and supplies middle gluteus and biceps femoris.
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The internal pudic artery supplies the bladder, urethra, obturator internus, retractor ani and coccygeus and passes down the ischial arch in the male and divides into dorsal and deep arteries of penis. The deep artery of the penis supplies the cavernous tissue of the penis. The dorsal artery passes on the dorsum penis along with a vein and a nerve. The internal pudic artery detaches in the female a large posterior uterine artery to supply the uterus and terminates as the artery of clitoris.
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Internal iliac vein: It is a satellite to the internal iliac artery draining venous blood from the pelvic organs. At the pelvic inlet it joins the external iliac vein to form the common iliac vein, which joins with its fellow to form the posterior vena cava.
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Lumbo-Sacral plexus: The posterior part of the lumbo-sacral plexus formed by the union of the ventral primary branches of the sixth lumbar, first and second sacral spinal nerves is seen above the greater sciatic foramen.
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Pudic and Posterior haemorrhoidal nerves: Ventral primary branches of the third and fourth sacral spinal nerves unite to form a common cord which divides into the posterior haemorrhoidal nerve to supply the rectum and pudic nerve which accompanies the artery over the dorsal aspect of the penis to supply it.
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Retractor ani: It is a flat muscle arising from the ischiatic spine and sacrosciatic ligament, passes upward and backward ends under the sphincter ani externus. Trace the branch from the pudic nerve to the muscle.
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Obturator internus: It arises from the pelvic face of the pubis and ischium around the obturator foramen. The muscle fibres converge and form a tendon, which leaves the foramen and joins the tendon of obturator externus, which is outside the pelvis to be inserted to the trochanteric fossa. Insertion should be examined later.
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Obturator nerve: This nerve arises from the anterior part of the lumbosacral plexus, which is deeply placed, between the sublumbar muscles, which should be examined later. The nerve passes obliquely downward and backward on the pelvic face of the ilium, enters the anterior part of the obturator foramen and supplies a branch to obturator internus and disappears in the muscles on the medial aspect of the thigh, which should be examined later.
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External iliac vein: It is a satellite of the artery behind which inlet down ward and backward, reaches the anterior border of the pubis, gains the space between the two heads of sartorius and enters the femoral canal to be continued as femoral artery.
Dissection
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Examine the peritoneum covering the abdominal wall in front.
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In front of the pelvic inlet, the parietal peritoneum dips to form the vaginal ring where it invaginates into the inguinal canal to form the tunica vaginalis to cover the spermatic cord and the testicle.
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No further disturbance should be made at this stage to the walls of the inguinal canal. The collateral branches of the external iliac artery should now be examined.
Circumflex iliac artery
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It is the first collateral branch of the external iliac artery arising from its lateral face at its origin passes outwards to the lateral angle of the ilium and divides into superior and inferior branches.
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The superior branch runs downward and forward on the internal oblique muscle of the abdomen. It supplies the transversus abdominis, obliquus abdominis muscles and the skin of the flank.
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The inferior branch supplies ilio-posas, perforates the abdominal wall and descends on the deep face of the tensor fascialata supplying branches to it and the prefemoral lymph gland and terminates in skin in front of the thigh.
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A common trunk arises from the anterior face of the external iliac above the pubis and divides into the prepubic and deep femoral arteries. The deep femoral artery passes backwards under the pubis to supply the muscles of the medial aspect of thigh, which should be examined later.
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The prepubic artery is small, passes forward and divides into the external pudic and posterior abdominal arteries at the internal inguinal ring.
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The posterior abdominal artery crosses the spermatic cord, passes forward on the deep face of rectus abdominis supplying branches to it and the internal oblique muscle. The artery passes forward and anastomoses with the branches of the anterior abdominal artery.
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The artery of the cord, a very fine artery usually arises from the posterior abdominal artery and passes along the posterior border of cremaster externus muscle to supply that muscle. This artery may arise from the external iliac or the perpubic or the Common trunk of prepubic and deep femoral.
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The extenral pudic artery in the male descends into the inguinal canal and passes along the posterior border of the spermatic cord, leaves the canal by the external inguinal ring, reaches the scrotum and divides into the subcutaneous abdominal artery and branches to scrotum.
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The subcutaneous abdominal artery passes forward, supplies branches to the scrotum, the superficial inguinal lymph gland and skin and accompanies the satellite vein on the tunica abdominalis for variable distances.
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In the female, the external pudic artery passes through the rudimentary inguinal canal as the mammary artery to supply the mammary gland.
Abdominal muscles
Dissection
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Cut the aponeurosis of the transverse abdominis close to where its muscle fibres terminate the reflect the muscle upwards. Do not disturb the peritoneum covering the posteromedial part of the internal oblique. Note the extent of the internal oblique muscle.
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Prepubic tendon: This is the common tendon of insertion of the oblique and rectus abdominal muscles of both sides. It is principally the common tendon of insertion of the two recti abdominis, which received on its lateral margins the insertion of the aponeuroses of the oblique muscles. It is in the form a strong thick band attached to the anterior borders of the pubic bones. It gives origin to the pectineus and gracilis.
Dissection
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Cut the aponeurosis of the internal oblique close to where its muscle fibres terminate and reflect the muscle backwards. Now note the external oblique muscle and its aponeurosis. Note the linea transversae. Note also the linea alba and see now the transverse and oblique muscles are inserted to it.
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Remove the peritoneum covering the internal oblique muscle and note how the abdominal inguinal ring is formed.
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Inguinal canal: It is a narrow oblique passage in the posterior part of abdominal wall on the medial aspect of the thigh.
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It extends downwards, forwards and medially from the abdominal inguinal ring to the subcutaneous inguinal ring. Its anterior wall is formed by the fleshy posterior part of internal oblique and the posterior wall by inguinal ligament.
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The average length of the canal may be 5 to 10cm. The abdominal inguinal ring is an oblique slit above, formed by the margin of the internal oblique in front and the inguinal ligament behind. The subcutaneous inguinal ring is a large well-defined slit, below in the aponeurosis of the external oblique, lateral to the prepubic tendon and can be seen at a later stage.
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In the male, the canal lodges the spermatic cord with the tunica vaginalis, cremaster externus and artery of the cord. In addition it accommodates the external pudic vessels and external spermatic nerve. In the female, the canal is very narrow containing the mammary vessels and nerves.
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Cremaster externus: This muscle is derived from the iliac fascia. It is placed on the lateral face of the tunica vaginalis to which it is attached.
Dissection
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Slit the parietal layer of tunica vaginalis of the spermatic cord and evert it with the cremaster externus.
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Spermatic cord: The spermatic cord is exposed. Examine the structures forming the cord, covered by the visceral layer of the tunica vaginalis.
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The cord consists of an anterior part containing the internal spermatic vessels, nerves, lymphatics and the cremaster internus mucles and the posterior part containing the ductus deferens.
Dissection
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Reflect the internal oblique forwards, which exposes the aponeurosis of the external oblique. Now examine the subcutaneous inguinal ring lateral to the prepubic tendon.
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Clean and examine the continuity between the prepubic tendon and the reflected part of the aponeurosis of external oblique to form the inguinal ligament.
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Inguinal ligament: It is otherwise called Poupart's ligament. It is the reflected part of the aponeurosis of the external oblique from the lateral margin of perpubic tendon. It is a thick glistening aponeurosis, which passes up on the medial aspect of the thigh to be inserted to lateral angle of the ilium. It forms the posterior wall of inguinal canal.
Dissection
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Lift the testicle from the scrotal bag and slit the parietal layer of tunica vaginalis along the anterior border of the testicle. Evert the flaps of the parietal layer backwards where they become continous with the visceral layer along the posterior or epididymal border of the testicle.
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Testicle and Epididymis:Testicle is enlongated and oval having the lower end of the spermatic cord attached to is upper pole. Along its posterior border is the epididymis, which overlaps its lateral face. The head of the epididymis is enlarged, attached to the upper pole of the testicle. The body of the epididymis is band like attached to the posterior border of the testicle. The lower end of the body of the epididymis is curved and narrow forming its tail, which is continued upwards by the ductus deferens.
Dissection
Remove the abdominal muscles by cutting their attachments including the prepubic tendon. Remove the penis and testicle. Clean tand remove the fascia and peritoneum covering the sublumbar muscles, but retain the fascia covering iliopsoas since one head of sartorius arises from that fascia. Only part of these muscles is availabe for examination.
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Psoas minor: It lies on the ventrolateral aspect of the bodies of lumbar vertebrae towards the median line related to the vena cava and the aorta. Its tendon crosses the pelvic inlet to be inserted to the psoas tubrecle.
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Psoas major: It is a larger muscle situated lateral to the preceding under the transverse processes of the lumbar vertebrae. It at first lies in a groove formed by the two parts of iliacus and blends with iliacus to form the iliopsoas placed on the anterior face of the ilium and is inserted to the medial trochanter of the femur. The insertion will be noted at a later stage.
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Quadratus lumborum: It is partly covered by the preceding and extends laterally under the transverse processes of the lumbar vertebrae and is inserted to the wing of sacrum.
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Intertransversales lumborum: These thin strands extend between the transverse processes of the lumbar vertebrae.
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Iliacus: It is situated on the anterior face of the ilium and consists of two parts between which the tendon of psoas major passes and blends with it to form the iliopsoas.
Dissection
Separate the psoas minor and major and work in the interspace till you see a large nerve plexus and follow it backwards in front of the ilium where the plexus detaches three nerves iliocomuscular femoral and obturator nerves.
Dissection
Cut the tendon of psoas major, reflect it towards the origin and note the iliacomuscular nerve terminating in iliacus.
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Femoral nerve: It is a very large nerve arising from the plexus. It passes vertically downwards in the groove of iliacus covered by the psoas major. It lies in front of the external iliac artery. Above the pubis, it detaches the saphenous nerve, which accompanies the femoral artery into femoral canal. The femoral nerve enters quadriceps with the anterior femoral artery, which arises from the femoral artery. These structures can be examined at later stage.
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