Pelvic diaphragm; Pelvic floor

The pelvic diaphragm is a muscular and connective tissue structure that forms the caudal boundary of the pelvic cavity. It is a crucial muscular structure that supports the terminal parts of the digestive and urogenital tracts. It maintains the integrity of the pelvic cavity and plays a role in defecation, urination, and parturition.

Main Components

The two principal muscular components of the pelvic diaphragm in most domestic animals are:

• Levator ani muscle:

  • Origin: Medial part of the ilium and the dorsal surface of the pubis and pelvic symphysis.

  • Insertion: Caudal vertebrae and external anal sphincter.

  • Function: Aids in defecation by pulling the rectum cranially and ventrally; helps close the pelvic outlet.

  • Characteristics: Thin, flat, and broad; sometimes difficult to distinguish from adjacent muscles.

• Coccygeus muscle:

  • Origin: Ischiatic spine.

  • Insertion: Transverse processes of the second to fifth caudal vertebrae.

  • Function: Pulls the tail ventrally and laterally; stabilizes the tail during defecation.

  • Characteristics: Thicker and more lateral than the levator ani.

Associated Structures

• Internal fascia of pelvic diaphragm

• External fascia of pelvic diaphragm

• External anal sphincter: Not part of the pelvic diaphragm per se, but functionally and anatomically associated. It provides voluntary control over defecation.

• Deep fascia of the pelvis: Encases and supports the pelvic diaphragm, contributing to its structural integrity.

• Perineal body: Fibromuscular node where various pelvic and perineal muscles converge, reinforcing the pelvic floor, particularly in females.

Clinical Relevance

In veterinary medicine, the pelvic diaphragm's integrity is crucial. Weakness or rupture (e.g., perineal hernia in dogs) can result in displacement of pelvic organs, requiring surgical repair. Species-specific anatomy must be understood for effective diagnosis and treatment.