• Gross (macroscopic) anatomy - structures visible to the naked eye
• Microscopic anatomy (histology) - tissues and cells examined under a microscope
• Developmental anatomy (embryology) - how structures form from conception onward
• Neuroanatomy - the nervous system specifically
• Regional anatomy - studying all structures in a given body region (e.g. the thorax)
• Systemic anatomy - studying body systems (e.g. the cardiovascular system) as a whole

The Diaphragm

Overview

Origin (Three Parts)

• Medial arcuate ligament - from the body of L2 to its transverse process (over psoas major)
• Lateral arcuate ligament - from the transverse process of L2 to the tip of rib 12 (over quadratus lumborum)

Openings (Apertures)

Memory aid: "I 8 (ate) 10 eggs At 12" - IVC at T8, Esophagus at T10, Aorta at T12.

• Foramen of Morgagni (sternocostal hiatus) - between sternal and costal parts; transmits lymphatic vessels from liver to anterior phrenic nodes
• Lumbocostal trigone (Bochdalek triangle) - a muscular deficiency between costal and lumbar parts; a common site of congenital diaphragmatic hernia

Blood Supply

Innervation

• Motor + central sensory: Phrenic nerves (C3, C4, C5 - "C3, 4, 5 keeps the diaphragm alive")
• The phrenic nerves course along the lateral surface of the fibrous pericardium, anterior to the lung roots, reaching the thoracic surface of the diaphragm
• Each phrenic nerve divides into: sternal branch (anteromedial), anterolateral branch, and posterior branch (splits into posterolateral and crural)
• Peripheral sensory: Lower intercostal nerves (T5-T11) and subcostal nerve supply the peripheral diaphragm

Function

• Primary muscle of respiration. On contraction, the domes flatten, increasing thoracic volume and drawing air into the lungs (inspiration). Relaxation allows the domes to rise, decreasing thoracic volume (expiration).
• Also assists with defecation, micturition, vomiting, and parturition (increasing intra-abdominal pressure).

Clinical Relevance

• Hiatal hernia - herniation through the esophageal hiatus (sliding type most common; paraesophageal type less common). See diagram above, panel B.
• Congenital diaphragmatic hernia (CDH) - most often through the Bochdalek triangle (posterolateral), causing bowel herniation into the thorax and pulmonary hypoplasia.
• Referred pain - diaphragmatic irritation (e.g., subphrenic abscess) refers pain to the shoulder tip via the phrenic nerve (C3-C5 dermatome).
• Phrenic nerve palsy - causes ipsilateral hemidiaphragm paralysis and elevation, visible on chest X-ray.

• Gray's Anatomy for Students, p. 164
• Fischer's Mastery of Surgery (8th ed.), p. 2588-2590

Mid-Inguinal Point vs. Midpoint of the Inguinal Ligament

Midpoint of the Inguinal Ligament

• Definition: Midpoint between the Anterior Superior Iliac Spine (ASIS) and the Pubic Tubercle
• The inguinal ligament itself runs from the ASIS to the pubic tubercle, so this is simply its geometric midpoint
• Structure lying here: The femoral artery - it reliably bisects the inguinal ligament at its midpoint
• Also used as the landmark for locating the femoral nerve (just lateral to femoral artery) and femoral vein (just medial)

"Femoral artery reliably bisects the inguinal ligament at its midpoint." - Fischer's Mastery of Surgery, 8th ed.

"Locate the midpoint of a straight line between the anterior superior iliac spine and pubic tubercle... insert the needle vertically [for femoral artery cannulation]." - Color Atlas of Human Anatomy

Mid-Inguinal Point

• Definition: Midpoint between the ASIS and the Pubic Symphysis (not the pubic tubercle)
• Structure lying here: The femoral pulse / deep inguinal ring (approximately ½ inch above this point)
• The deep inguinal ring, where an indirect inguinal hernia originates, lies about 1.25 cm (½ inch) above and lateral to the mid-inguinal point

"½ inch above the mid-inguinal point, which is the midpoint between anterior superior iliac spine and symphysis pubis." - S. Das Manual on Clinical Surgery, 13th ed.

Side-by-Side Comparison

Why the Confusion?

• Midpoint of inguinal ligament (ASIS to pubic tubercle) = over the femoral artery
• Mid-inguinal point (ASIS to pubic symphysis) = slightly medial, over the femoral canal/deep ring region

Note: Some older texts (including some editions of Mulholland's Surgery) use the term "mid-inguinal point" loosely to mean midpoint of the inguinal ligament. Always clarify which definition is being used in context.

Mnemonic

"MidLigament = Artery; MidInguinal = deep ring"

• Ligament midpoint → Femoral Artery (L for Ligament, A for Artery)
• Mid-Inguinal point → Deep Inguinal ring (both start with I)

• S. Das Manual on Clinical Surgery, 13th ed., p. 604
• Fischer's Mastery of Surgery, 8th ed., p. 6469
• Color Atlas of Human Anatomy, p. 582

Abduction

Definition

• For fingers and toes, abduction means spreading them away from the middle digit (middle finger for the hand; second toe for the foot), not away from the body midline
• For the thumb, abduction is movement anteriorly (away from the palm plane), which is a special case due to the thumb's rotated orientation

Plane and Axis

Abduction at Different Joints

Mnemonic for hand interossei: DAB = Dorsal interossei ABduct; PAD = Palmar interossei ADduct

Abduction of the Femur - Two Scenarios

• Abduction of femur on a fixed pelvis - the leg swings outward (walking, standing on one leg)
• Abduction of pelvis on a fixed femur - the pelvis tilts laterally, as in single-leg stance during gait; this is what the gluteus medius and minimus do to prevent the pelvis from dropping (Trendelenburg mechanism)

Shoulder Abduction - Special Note

1. 0-90° - glenohumeral joint abduction (supraspinatus initiates; deltoid continues)
2. 90-180° - requires upward rotation of the scapula (serratus anterior + trapezius), plus lateral rotation of the humerus to clear the greater tubercle from under the acromion

Circumduction

Clinical Relevance

• Gray's Anatomy for Students, p. 640-641