Perineal Membrane

Definition and Terminology

Attachments

• Laterally: attached on each side to the ischiopubic rami (inferior pubic and ischial rami), spanning between the right and left pubic arch from the pubis to the ischial tuberosities.
• Posteriorly: has a free posterior border, which is anchored in the midline to the perineal body.
• Anteriorly: a small gap exists between the membrane and the inferior pubic ligament (associated with the pubic symphysis). The anterior edge of the perineal membrane is close to, but separated from, the inferior pubic ligament by this narrow interval.

Openings / Perforations

1. Urethra - passes through a circular hiatus as it travels from the pelvic cavity to the perineum (in both sexes).
2. Vagina (in females only) - passes through a second hiatus just posterior to the urethral opening.

Deep Perineal Pouch (Deep Perineal Space)

Muscles of the Deep Perineal Pouch

Neurovascular contents of the deep perineal pouch

• Branches of the pudendal nerve and internal pudendal vessels
• Bulbo-urethral (Cowper's) glands in males (their ducts pierce the perineal membrane to reach the urethra)

Relationships and Pouches

Functions

1. Supports external genitalia - the roots/bulbs of the penis (or clitoris and vestibular bulbs) attach to the inferior surface of the membrane.
2. Pelvic floor support - the parts of the membrane enclosed by the urogenital hiatus of the levator ani contribute to the pelvic floor and provide support to urogenital viscera above (bladder, uterus, vagina).
3. Urethral continence - the external urethral sphincter in the deep perineal pouch compresses the membranous urethra.
4. Stabilizes the perineal body - via attachment of the deep transverse perineal muscles at the posterior free border.
5. Provides a passage for the urethra (and vagina in females) between the pelvis and perineum.

Perineal Body

• Deep transverse perineal muscles
• Superficial transverse perineal muscles
• External anal sphincter
• Bulbospongiosus muscles
• Sphincter urethrovaginalis (in females)
• Posterior end of the urogenital hiatus of levator ani

Sex Differences at a Glance

The Stomach - Complete Anatomy

1. Parts of the Stomach

• Lesser curvature (right/medial border) - attachment for lesser omentum; contains the angular incisure (incisura angularis), a bend that marks the junction of body and pyloric part
• Greater curvature (left/lateral border) - attachment for gastrosplenic ligament and greater omentum
• Cardiac notch - the superior angle where the esophagus enters the stomach

2. Blood Supply

Arteries

• Short gastric arteries (vasa brevia) - 5-7 in number, arise from the terminal branches of the splenic artery and the left gastroepiploic artery; supply the fundus

• Posterior gastric artery - arises from the splenic artery (not always present); supplies the posterior gastric wall

Veins

• Veins along the lesser curvature (right and left gastric veins) drain into the portal vein
• Veins along the greater curvature (right and left gastroepiploic veins) drain into the splenic vein
• The left gastric (coronary) vein runs along the lesser curvature toward the esophagus, then passes left to right to join the portal vein. This vein becomes markedly dilated in portal hypertension, forming esophageal varices. - Bailey and Love's

3. Nerve Supply

Extrinsic Innervation

Parasympathetic (Vagus Nerve - CN X)

• The vagal plexus around the esophagus condenses into trunks at the esophageal hiatus
• The left (anterior) vagus - lies on the anterior surface of the stomach; gives off the hepatic branch (in gastrohepatic ligament to liver) and continues as the anterior nerve of Latarjet along the lesser curvature
• The right (posterior) vagus - lies on the posterior surface; gives off the celiac branch (to celiac plexus) and continues as the posterior nerve of Latarjet along the lesser curvature
• The nerves of Latarjet give segmental branches to the body of the stomach, then terminate near the angularis incisura as the "crow's foot," sending branches to the antro-pyloric region
• The criminal nerve of Grassi is the first branch of the right posterior vagus to the posterior fundus - it arises above the esophageal hiatus and is easily missed during vagotomy, causing recurrent ulcers if left undivided
• 90% of vagal fibers are afferent (sensory, to brain); efferent fibers originate in the dorsal nucleus of the medulla and synapse in the myenteric/submucosal plexuses
• Functions: receptive relaxation, gastric motility, gastric acid secretion, mucosal blood flow, cytoprotection - Sabiston

Sympathetic

• Originates from spinal levels T5-T10
• Travels in the greater splanchnic nerves to the celiac ganglion
• Postganglionic fibers travel along the blood vessels to innervate the stomach
• Contains afferent pain fibers (pain referred to the epigastrium / T5-T10 dermatomes) and motor fibers to the pyloric sphincter

Intrinsic (Enteric) Nervous System

4. Lymphatic Drainage

• Gastric cancers may metastasize to any of the four nodal groups, regardless of tumor location
• The extensive submucosal lymphatic plexus means malignant cells can be found several centimeters beyond the gross tumor margin - this determines resection margins
• Lymphatics of the cardia communicate freely with those of the esophagus - Bailey and Love's

5. Applied Anatomy

Peptic Ulcer Disease

• Duodenal ulcers occur most often in the first part of the duodenum (duodenal cap/ampulla)
• A bleeding posterior duodenal ulcer erodes the gastroduodenal artery, which runs behind the first part of the duodenum - this is the anatomical basis for life-threatening hemorrhage
• Pain from peptic ulcers is referred to the epigastrium (T5-T10 dermatomes) via sympathetic afferents

Vagotomy (for peptic ulcer)

• Truncal vagotomy: division above the hepatic and celiac branches - removes all gastric vagal innervation but also denervates liver, biliary system, and gut; requires a drainage procedure (pyloroplasty or gastroenterostomy)
• Selective vagotomy: division below the hepatic and celiac branches - spares liver and celiac innervation but still requires drainage
• Highly selective (proximal gastric) vagotomy: divides the "crow's foot" branches to the body only, preserving antro-pyloric innervation - no drainage procedure needed
• The criminal nerve of Grassi must be divided or recurrent ulcers result

Gastric Cancer

• Spreads via: (1) direct invasion of adjacent organs (pancreas, liver, transverse colon), (2) lymphatic spread (D1/D2 node dissection), (3) haematogenous spread (liver most common), (4) transcoelomic/peritoneal spread
• Peritoneal spread may deposit on the ovaries (Krukenberg tumours) or at the umbilicus (Sister Joseph's nodule / Sister Mary Joseph nodule)
• Late detection leads to poor prognosis: overall 5-year survival is only 5-20% - Gray's Anatomy for Students

Portal Hypertension

• The left gastric (coronary) vein normally drains into the portal vein. In portal hypertension, it becomes dilated and reverses flow, creating a portosystemic anastomosis at the gastroesophageal junction - forming esophageal and gastric varices prone to catastrophic hemorrhage

Gastric Conduit (Esophageal Surgery)

• After esophagectomy, the stomach is the preferred organ for reconstruction - it is tubularized using the right gastroepiploic arcade
• The rich dual-curvature blood supply means even a tubularized stomach survives well on a single pedicle (right gastroepiploic artery)
• The left gastroepiploic arcade is often variably incomplete, which is relevant when planning the conduit

Short Gastric Vessels in Splenectomy

• The short gastric arteries (vasa brevia) run in the gastrosplenic ligament. During splenectomy they must be ligated carefully to avoid bleeding and inadvertent gastric injury

Nerve Supply of the Tongue

Embryological Basis

• 1st arch → mandibular nerve (V3) - general sensation, anterior 2/3
• 2nd arch (facial, CN VII) → chorda tympani - taste, anterior 2/3 (the 2nd arch is overgrown by the 3rd, so CN VII doesn't supply mucosa, only taste buds)
• 3rd arch → glossopharyngeal (CN IX) - sensation + taste, posterior 1/3
• 4th arch → vagus (CN X) - small area near epiglottis/valleculae
• Occipital somite migrants bring hypoglossal (CN XII) for muscle supply
• The Developing Human (Moore's Embryology)

I. Sensory Nerve Supply

A. General Sensation (Touch, Pain, Temperature)

B. Special Sensation (Taste)

• K.J. Lee's Essential Otolaryngology; Developing Human Embryology

II. Motor Nerve Supply

Hypoglossal Nerve (CN XII) - ALL tongue muscles EXCEPT palatoglossus

• Exits skull via hypoglossal canal (alongside C1-2 fibers)
• Crosses over the internal and external carotid arteries
• Passes between mylohyoid and hyoglossus muscles
• Lies below the submandibular gland, submandibular duct, and lingual nerve
• Passes deep to the lingual nerve along the genioglossus toward the tip of the tongue
• Gives branches to styloglossus, hyoglossus, and genioglossus; slender rami ascend into intrinsic muscles

Exception - Palatoglossus

• Palatoglossus (the muscle forming the anterior pillar of the fauces) is supplied by the vagus nerve (CN X) via the pharyngeal branch to the pharyngeal plexus - NOT the hypoglossal nerve.
• This is because palatoglossus is functionally a muscle of the soft palate, not the tongue.

III. Autonomic Supply

Summary Diagram (Simplified)

TONGUE
├── Anterior 2/3
│   ├── General sensation    → Lingual nerve (V3)
│   ├── Taste (fungiform/foliate) → Chorda tympani (CN VII via lingual nerve)
│   └── Taste (circumvallate) → CN IX (exception!)
│
├── Posterior 1/3
│   ├── General sensation    → CN IX (glossopharyngeal)
│   └── Taste               → CN IX
│
├── Valleculae / epiglottis
│   └── General + taste     → Internal laryngeal nerve (CN X)
│
└── MOTOR (all muscles)
    ├── ALL tongue muscles   → CN XII (hypoglossal)
    └── Palatoglossus ONLY  → CN X (vagus via pharyngeal plexus)

IV. Applied Anatomy / Clinical Correlates

1. Lingual Nerve Injury

• Lesion proximal to where chorda tympani joins: Loss of general sensation (touch, pain, temperature) from anterior 2/3 of tongue + loss of taste from anterior 2/3 + reduced submandibular and sublingual salivary secretion
• Lesion distal to where chorda tympani joins (i.e. after it has already joined): Loss of general sensation from anterior 2/3 only; taste and salivary loss also occur

2. Hypoglossal Nerve Palsy (CN XII)

• Lower motor neuron lesion: tongue deviates toward the side of the lesion on protrusion (due to paralysis of ipsilateral genioglossus, which normally pushes the tongue to the opposite side)
• Chronic LMN lesion: ipsilateral wasting and fasciculation of tongue
• UMN lesion: deviation may be contralateral; no wasting
• Relevant in head and neck cancer - CN XII involvement by primary tumor or level I/II neck nodes causes tongue weakness and deviation - Mulholland and Greenfield's Surgery

3. Surgical Landmark

4. Taste Pathway Central Connections