Anatomy of testis

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I now have all the information needed for a comprehensive answer. Here is the complete anatomy of the testis:

Anatomy of the Testis

1. Overview and Dimensions

The testis is a paired male gonad located in the scrotum. At sexual maturity, each testis is approximately 4 × 3 × 2.5 cm (or ~5 cm long and 3 cm wide), with an average volume of 18 mL (range 12-30 mL). The combined weight of the testis and epididymis is approximately 20-30 g. Volume can be estimated using an orchidometer or ultrasound formula: length × width × height × 0.71.

Lateral view of testis and epididymis showing appendix of epididymis, appendix of testis, mediastinum testis, head/body/tail of epididymis, and ductus deferens

2. Coverings (Tunics)

From outside in:

Layer	Details
Scrotal skin	Thin, rugose skin
Tunica dartos	Smooth muscle layer responsible for scrotal rugosity
External spermatic fascia	Derived from external oblique aponeurosis
Cremasteric fascia & Cremaster muscle	From internal oblique; responsible for cremasteric reflex (L1/L2)
Internal spermatic fascia	Derived from transversalis fascia
Tunica vaginalis (parietal layer)	Serous lining; separated from visceral layer by the serous cavity of the testis
Tunica vaginalis (visceral layer)	Closely adherent to the testis anteriorly and laterally
Tunica albuginea	Dense fibrous capsule; tough, rubbery consistency; the innermost covering directly on testicular tissue

Between the visceral and parietal layers of the tunica vaginalis lies a small, mesothelium-lined serous cavity containing a scant amount of fluid (epididymal sinus). Abnormal fluid accumulation here is a hydrocele.

Cross-section showing all layers: scrotal skin, tunica dartos, external spermatic fascia, cremaster muscle, cremasteric fascia, internal spermatic fascia, tunica vaginalis (parietal and visceral layers), and internal testicular structures including convoluted seminiferous tubules, testicular septa, rete testis, and blood vessels

3. Internal Structure

Tunica albuginea - the dense fibrous capsule sends fibrous septa radially inward toward the posterior aspect
Mediastinum testis - the posterior thickening of the tunica albuginea where the septa converge; houses the rete testis and major vessels
Lobules - the septa divide the testis into approximately 250-370 wedge-shaped lobules
Seminiferous tubules - each lobule contains 1-4 highly convoluted seminiferous tubules, each about 60 cm long when uncoiled; this is where spermatogenesis occurs
Rete testis - an anastomosing network of channels within the mediastinum testis that receives outflow from the seminiferous tubules
Efferent ductules - approximately 10-15 efferent ductules pass from the rete testis to the head of the epididymis

Internal structure of testis showing tunica albuginea, testicular septa, lobules, rete testis in the mediastinum, efferent ductules, convoluted seminiferous tubules, epididymal duct, and ductus deferens, along with testicular artery and pampiniform plexus

4. Histology

The seminiferous tubule has a basement membrane supported by connective and elastic tissue, bearing two cell populations:

Sertoli (sustentacular) cells - supporting cells; secrete Anti-Mullerian Hormone (AMH); form the blood-testis barrier
Spermatogenic cells - the precursors of mature spermatozoa (spermatogonia → primary spermatocyte → secondary spermatocyte → spermatid → spermatozoon)

The stroma between seminiferous tubules contains connective tissue with interstitial Leydig cells, which synthesize testosterone in response to LH.

5. Relations

The testis is closely attached posterolaterally to the epididymis, particularly at its upper and lower poles
The appendix testis (a small pedunculated/sessile remnant of the paramesonephric duct) is located at the upper pole - it can undergo torsion
The epididymis runs along the posterior surface: head (caput) at the upper pole → body (corpus) → tail (cauda) at the lower pole, which is continuous with the ductus deferens

6. Blood Supply

Arterial (3 arteries anastomose with each other)

Artery	Origin
Testicular artery (internal spermatic artery)	Directly from the abdominal aorta, just below the renal arteries
Artery of the ductus deferens	Internal iliac (hypogastric) artery
Cremasteric artery	Inferior epigastric artery

The testicular artery arises at the level of L2, reflecting the gonadal embryological origin near the kidneys.

Venous

Blood drains into the pampiniform plexus - an elongated venous network surrounding the testicular artery within the spermatic cord. This plexus acts as a counter-current heat exchanger, cooling arterial blood to keep the testis slightly below body temperature (essential for spermatogenesis).

At the internal inguinal ring, the pampiniform plexus converges to form the spermatic vein (testicular vein):

Right testicular vein → enters the inferior vena cava (IVC) just below the right renal vein (oblique angle)
Left testicular vein → enters the left renal vein at a right angle - this creates a physiologically significant constriction prone to obstruction, explaining why varicocele is far more common on the left side

Spermatic cord vessels: testicular artery (red), pampiniform plexus (blue), cremasteric artery, artery and veins of the ductus deferens

7. Lymphatic Drainage

Testis and epididymis → lymphatics follow the testicular vessels → drain to lumbar (para-aortic) lymph nodes (at L1-L2 level)
Scrotum and coverings → drain to superficial inguinal lymph nodes

Clinical note: This distinction is vital - testicular tumors metastasize to retroperitoneal para-aortic nodes, NOT to inguinal nodes (unless the scrotal skin is invaded or prior inguinal surgery has disrupted lymphatics).

Lymphatic drainage diagram showing testicular/epididymal lymphatics going to lumbar para-aortic nodes (following testicular artery), versus scrotal/covering lymphatics draining to superficial inguinal nodes

8. Nerve Supply

Component	Nerve
Sensory (and autonomic)	Testicular plexus (T10-T11) via branches from the renal and aortic plexuses accompanying the testicular artery
Cremasteric reflex (motor)	Genitofemoral nerve (L1-L2) - the genital branch
Referred pain	Because testicular nerves arise at T10, pain from the testis is referred to the umbilical region (T10 dermatome)

9. Spermatic Cord Contents

The spermatic cord suspends the testis and runs from the deep (internal) inguinal ring to the posterior border of the testis. Its contents include:

Vas deferens (ductus deferens)
Testicular artery
Pampiniform plexus (testicular veins)
Cremasteric artery and artery of vas deferens
Genital branch of genitofemoral nerve
Sympathetic nerve fibers
Lymphatic vessels

Sources:

General Anatomy and Musculoskeletal System, THIEME Atlas of Anatomy, pp. 247-248
Smith and Tanagho's General Urology, 19th Edition, p. 27
Campbell-Walsh-Wein Urology, 3-Volume Set

Also add source BDC

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Unfortunately, BD Chaurasia's Human Anatomy is not available in the medical textbook library. The anatomy books currently in the library are:

THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System
Gray's Anatomy for Students
Netter's Atlas of Human Anatomy
Color Atlas of Human Anatomy (Vols 1, 2, 3 - Sobotta/Schiebler)
Imaging Anatomy: Bones, Joints, Vessels and Nerves

BD Chaurasia (BDC) is not among them. Would you like me to:

Pull testis anatomy from Gray's Anatomy for Students - a very commonly used and authoritative reference that covers similar ground to BDC
Pull from Netter's Atlas - excellent for visual/diagram-based anatomy
Both - combine Gray's and Netter's to supplement the existing answer

Go for Both

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All four Netter diagrams retrieved. Here is the updated comprehensive answer incorporating Gray's Anatomy for Students and Netter's Atlas:

Anatomy of the Testis

Sources: THIEME Atlas | Smith & Tanagho's Urology | Campbell-Walsh-Wein | Gray's Anatomy for Students | Netter's Atlas of Human Anatomy

1. Overview and Dimensions

The testis is a paired male gonad that originally develops high on the posterior abdominal wall and then descends - normally before birth - through the inguinal canal into the scrotum. During this descent it carries its vessels, lymphatics, nerves, and ductus deferens with it. At sexual maturity, each testis measures approximately 4 × 3 × 2.5 cm (length ~5 cm, width ~3 cm), with an average volume of 18 mL (range 12-30 mL) and combined weight with epididymis of approximately 20-30 g.

Lateral surface view of testis and epididymis showing appendix testis, appendix of epididymis, mediastinum testis, head/body/tail of epididymis, and ductus deferens

2. Coverings of the Testis (from outside in)

Each testis is enclosed within the end of an elongated musculofascial pouch continuous with the anterior abdominal wall. The layers, from outermost to innermost, are:

Layer	Embryological Derivation
Scrotal skin	Labioscrotal swellings
Superficial (dartos) fascia	Superficial fascia of abdomen (Scarpa's fascia) - contains smooth muscle
External spermatic fascia	External oblique aponeurosis
Cremaster muscle and fascia	Internal oblique muscle - responsible for cremasteric reflex
Internal spermatic fascia	Transversalis fascia
Parietal layer of tunica vaginalis	Peritoneum (processus vaginalis)
Visceral layer of tunica vaginalis	Peritoneum - covers anterior and lateral surfaces of testis
Tunica albuginea	Dense fibrous capsule directly enclosing testicular tissue

The visceral and parietal layers of the tunica vaginalis are separated by a small serous cavity (sinus/cavity of testis). Abnormal accumulation of fluid here = hydrocele.

Netter's Lateral View showing the layers of the testis within the scrotum:

Netter's lateral view showing scrotal skin, superficial dartos fascia, external spermatic fascia, cremaster muscle and fascia, internal spermatic fascia, parietal and visceral layers of tunica vaginalis, and the testis with epididymis

THIEME cross-section showing all coverings and internal structure:

THIEME cross-section of testis within scrotum showing all layers: scrotal skin, tunica dartos, external spermatic fascia, cremaster muscle, cremasteric fascia, internal spermatic fascia, tunica vaginalis (parietal and visceral), tunica albuginea, testicular septa, seminiferous tubules, rete testis, epididymal sinus, and neurovascular structures

Netter's cross-section for comparison:

Netter's cross-section showing scrotal skin, superficial dartos fascia, external spermatic fascia, cremaster muscle and fascia, internal spermatic fascia, parietal and visceral layers of tunica vaginalis, tunica albuginea, septa, lobules, rete testis in mediastinum testis, sinus of epididymis, epididymis, and ductus deferens

3. Internal Structure

Tunica albuginea - thick dense fibrous capsule; invaginates posteriorly to form the mediastinum testis
Mediastinum testis - the posterior connective tissue wedge housing the rete testis and main vessels; septa radiate from here
Testicular septa - fibrous septa extending from the tunica albuginea toward the mediastinum, dividing the testis into ~250-370 wedge-shaped lobules
Seminiferous tubules - each lobule contains 1-4 highly coiled tubules, each ~60 cm long; 400-600 total per testis; both ends become straight tubules that drain into the rete testis
Rete testis - anastomosing channel network within the mediastinum testis; receives drainage from all seminiferous tubules
Efferent ductules - 12-20 ductules arise from the upper end of the rete testis, pierce the tunica albuginea, and connect with the head of the epididymis

Netter's Frontal Section showing internal structure:

Netter's frontal section of testis showing head/body/tail of epididymis, efferent ductules, rete testis in mediastinum testis, septa, tunica albuginea, lobules, aberrant ductule (vestigial mesonephric tubule), and ductus deferens

THIEME/Netter schema of tubular continuity:

Schema showing the pathway: seminiferous tubules → rete testis in mediastinum testis → efferent ductules → epididymal duct → ductus deferens, with aberrant ductule also labeled

Gray's Anatomy adds the key detail that the straight tubules at each end of the seminiferous tubules connect to the rete testis, which sits within "a thick, vertically oriented linear wedge of connective tissue (the mediastinum testis), projecting from the capsule into the posterior aspect of the gonad."

4. Histology

The seminiferous tubule wall contains:

Sertoli (sustentacular) cells - supporting cells; form the blood-testis barrier; secrete Anti-Mullerian Hormone (AMH) and androgen-binding protein
Spermatogenic cells - in progressive stages from basal to luminal: spermatogonia → primary spermatocyte → secondary spermatocyte → spermatid → spermatozoon

The interstitium between tubules contains Leydig cells (interstitial cells), which secrete testosterone in response to LH stimulation.

5. Relations

Closely attached posterolaterally to the epididymis (especially at upper and lower poles)
Appendix testis - small pedunculated remnant of the paramesonephric (Mullerian) duct at the upper pole; clinically may undergo torsion (most common cause of acute scrotum in prepubertal boys)
A midline scrotal raphe is visible on the skin; in some individuals it extends from the anal aperture over the scrotum to the frenulum of the glans penis

6. Blood Supply

Arterial - 3 arteries with anastomoses

Artery	Origin	Supply
Testicular (internal spermatic) artery	Abdominal aorta at L2, below renal arteries	Main supply to testis and epididymis
Artery of the ductus deferens	Internal iliac artery	Ductus deferens and epididymis
Cremasteric artery	Inferior epigastric artery	Coverings of testis

This three-vessel supply is the reason that ligation of the testicular artery alone (e.g., during varicocelectomy) does not always result in testicular atrophy.

Spermatic cord vascular anatomy showing testicular artery, pampiniform plexus (testicular veins), artery and veins of ductus deferens, cremasteric artery and cremasteric vein

Venous - Pampiniform Plexus

Venous blood drains into the pampiniform plexus - a network of veins surrounding the testicular artery, acting as a counter-current heat exchanger to maintain testicular temperature ~2-4°C below body temperature (required for spermatogenesis)
At the internal inguinal ring, the plexus coalesces into the testicular (spermatic) vein:
- Right testicular vein → IVC (at an oblique angle)
- Left testicular vein → left renal vein at a right angle - this creates resistance to outflow, which is why varicocele occurs predominantly on the left (90%)

7. Lymphatic Drainage

Structure	Drains To
Testis and epididymis	Lumbar (para-aortic) lymph nodes at L1-L2
Scrotum and testicular coverings	Superficial inguinal lymph nodes

Lymphatic drainage diagram showing testicular/epididymal lymphatics running with the testicular artery to lumbar para-aortic nodes, while scrotal/covering lymphatics drain to the superficial inguinal nodes

Clinical point (Gray's): Because the testis developed in the abdomen and carried its lymphatics with it during descent, testicular tumors metastasize to retroperitoneal para-aortic nodes, NOT inguinal nodes. Inguinal node involvement only occurs if the scrotal skin or tunica vaginalis is invaded, or if prior surgery has disrupted normal lymphatic channels. This is also why testicular tumors must NOT be removed via a scrotal incision.

8. Nerve Supply

Component	Nerve	Level
Autonomic and sensory (testis)	Testicular plexus (from renal and aortic plexuses) following the testicular artery	T10-T11
Cremasteric reflex (afferent)	Ilioinguinal nerve	L1
Cremasteric reflex (efferent/motor)	Genital branch of genitofemoral nerve	L1-L2

Because the testicular nerve supply arises at T10, pain from the testis is referred to the umbilical region (T10 dermatome). This is why a blow to the testis causes periumbilical pain, and why testicular torsion or tumor can occasionally present with abdominal pain.

9. Spermatic Cord

The spermatic cord runs from the deep inguinal ring to the posterior border of the testis. It is the "tube-shaped connection between the pouch in the scrotum and the abdominal wall" (Gray's). Contents:

Ductus (vas) deferens
Testicular artery
Pampiniform plexus of veins
Artery and vein of the ductus deferens
Cremasteric artery and vein
Genital branch of the genitofemoral nerve
Sympathetic nerve fibers (testicular plexus)
Lymphatic vessels

10. Descent of the Testis (Embryological Basis - Gray's)

The testis originally develops on the posterior abdominal wall. A fibrous cord - the gubernaculum - guides descent through the inguinal canal into the scrotum, typically completing by the last trimester of gestation. Arrest of descent = cryptorchidism (undescended testis):

Found in ~30% of premature births, 3-5% of term births
Usually completes descent spontaneously within 3 months after birth
Watchful waiting recommended until 6 months; referral if still undescended; orchiopexy typically performed between 6-12 months
During orchiopexy, the gubernaculum remnant (attaching the caudal pole of the testis to the scrotum) must be divided carefully

Sources:

General Anatomy and Musculoskeletal System, THIEME Atlas of Anatomy, pp. 247-248
Smith and Tanagho's General Urology, 19th Edition, p. 27
Campbell-Walsh-Wein Urology, 3-Volume Set
Gray's Anatomy for Students, pp. 327-328, 604, 7090-7116
Netter's Atlas of Human Anatomy, pp. 658-663

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