📝 STANDARD DESCRIPTION:
The 4 abdominal muscles (outside → inside):
1. External Abdominal Oblique — fibres run cranio-dorsal → caudo-ventral (like hands in pockets).
2. Internal Abdominal Oblique — fibres run cranio-ventral → caudo-dorsal (perpendicular to external).
3. Transversus Abdominis — deepest oblique; fibres run nearly horizontally.
4. Rectus Abdominis — long ventral strap muscle from sternum to pubis; enclosed in rectus sheath (formed by aponeuroses of the 3 obliques).
• All meet ventrally at the linea alba (white line) → standard ventral midline approach.
• Functions: support viscera, expiration, urination, defaecation, parturition.
📚 DETAILED DESCRIPTION:
ABDOMINAL WALL — THE FOUR-LAYER GIRDLE
The abdominal wall is built of four flat muscles arranged in concentric layers, plus the strap-like rectus abdominis on the midline. Their aponeuroses converge on the linea alba, a fibrous raphe running from the xiphoid to the prepubic tendon.
1. External Abdominal Oblique (M. obliquus externus abdominis):
• Origin: Lateral surfaces of the last 8-9 ribs and lumbodorsal fascia.
• Direction: Cranio-dorsal to caudo-ventral ('hands in your front pockets').
• Insertion: Linea alba and tuber coxae via a long aponeurosis (forms the inguinal ligament caudally).
2. Internal Abdominal Oblique (M. obliquus internus abdominis):
• Origin: Tuber coxae + lumbodorsal fascia.
• Direction: Cranio-ventral and ventral (perpendicular to external) → fan-shaped.
• Insertion: Last 4-5 ribs and linea alba.
3. Transversus Abdominis:
• Origin: Lumbar transverse processes + medial face of last few ribs.
• Direction: Almost horizontal ('belt fibres').
• Insertion: Linea alba.
4. Rectus Abdominis:
• Long, strap-like muscle on either side of linea alba from sternum to pubis.
• Crossed by tendinous intersections (3-5 in ox) → 'six pack' pattern.
• Enclosed within the rectus sheath (made by aponeuroses of the three obliques).
• Inserts into the prepubic tendon.
FUNCTIONS:
• Visceral support ('belly girdle').
• Expiratory pressure (pushing diaphragm cranially).
• Power generation for: parturition, defaecation, micturition, eructation, vomiting (in non-ruminants).
• Trunk flexion.
SURGICAL WINDOWS:
• Ventral midline (linea alba) — splits cleanly between the two recti; relatively avascular; the standard approach in small animals; in cattle used for caesarean in lateral recumbency.
• Right paramedian — through rectus, lateral to linea alba; for abomasal surgery.
• Right or Left Flank (Paralumbar fossa) — through all 3 obliques + transversus + peritoneum. Standard standing rumenotomy/caesarean. Grid technique splits muscle fibres along their direction → minimal bleeding, strong closure.
// COMPARATIVE ANALYSIS
| OX |
Tendinous intersections of rectus visible — 'six pack'. External oblique aponeurosis forms inguinal ligament. Left paralumbar fossa is the standard rumenotomy site; right-flank approaches are used for many intestinal, caecal and abomasal procedures. |
| HORSE |
Same 4 muscles. Caesarean technically harder (large size). Linea alba surgically less popular than flank. |
| DOG/CAT |
Ventral midline laparotomy is standard. Linea alba easily identified. |
CLINICAL RELEVANCE
Laparotomy: Ventral midline (small animals, dorsal recumbency calves) or left paralumbar incision (standard standing cow rumenotomy); the right flank is used for many intestinal, caecal and abomasal procedures. Hernias: Umbilical (linea alba defect at navel), Inguinal (through superficial inguinal ring), Ventral (post-trauma rupture). Pre-pubic tendon rupture (Mare): Late pregnancy emergency — ventral abdominal swelling, inability to foal.
