Note: BD Chaurasia's Human Anatomy (BDC) is not available in this textbook library. The anatomy content below is sourced from Gray's Anatomy for Students and the Color Atlas of Human Anatomy (Thieme, Vol. 2) - both standard references that cover the same material as BDC on this topic.

Penis - Anatomy

Overview

• Two corpora cavernosa (paired, dorsal)
• One corpus spongiosum (single, ventral) - contains the urethra

Parts of the Penis

1. Root (Attached Part)

• Two crura - proximal extensions of the corpora cavernosa, attached to the inferior pubic rami; each is surrounded by the ischiocavernosus muscle
• Bulb of the penis - the proximal thickened part of the corpus spongiosum; firmly connected to the perineal membrane (urogenital diaphragm) and covered by the bulbospongiosus muscle

2. Body (Free Part)

• Made up of the two fused corpora cavernosa (forming the bulk) and the corpus spongiosum lying in the ventral groove
• Covered by thin skin that contains no fat and is freely movable
• Supported by two ligaments:
  • Suspensory ligament of the penis - attached superiorly to the pubic symphysis
  • Fundiform ligament of the penis - attached above to the linea alba; splits below into two bands passing on either side of the penis

3. Glans Penis

• Formed by the expanded distal end of the corpus spongiosum projecting beyond the corpora cavernosa
• The rounded margin at its base is the corona of the glans
• The tip bears the external urethral orifice (slit-like opening)
• The skin over the body folds forward over the glans as the prepuce (foreskin); its inner layer forms the frenulum of the prepuce inferiorly

Internal Structure

Corpora Cavernosa

• Each enclosed in a thick fibrous sheath - tunica albuginea of the corpora cavernosa
• A median septum penis partially separates the two chambers
• Internally: vascular (cavernous) spaces lined by endothelium, embedded in a trabecular framework of collagen, elastic fibers, and smooth muscle
• Fed by helicine arteries (from the deep artery of the penis); these act as resistance vessels
• Blood drains to subfascial and epifascial veins

Corpus Spongiosum

• Enclosed in a thinner tunica albuginea of the corpus spongiosum
• Vascular spaces are viewed as continuations of the venous system
• Contains less prominent trabeculae than the corpora cavernosa
• Filling leads only to "soft" swelling - keeps the urethra open during ejaculation

Fascial Layers

• Fascia of the penis (Buck's fascia) - tough deep fascia surrounding all three corpora collectively
• Subcutaneous tissue of the penis - thin layer beneath the skin, contains no fat

Blood Supply

Nerve Supply

• Sensory: Dorsal nerve of the penis (branch of the pudendal nerve, S2-S4) - general somatic sensory
• Parasympathetic (erection): Pelvic splanchnic nerves (S2-S4) via the inferior hypogastric plexus - cause vasodilation and erection
• Sympathetic (emission/ejaculation): Lumbar sympathetic fibers (L1-L3) via inferior hypogastric plexus

Lymphatic Drainage

Erection

1. Parasympathetic stimulation (S2-S4) causes relaxation of helicine arteries
2. Blood fills the cavernous spaces of the corpora cavernosa
3. Venous outflow is simultaneously reduced (veno-occlusive mechanism)
4. The ejaculation reflex center (L2/L3) initiates emission and ejaculation when stimulation reaches threshold