The anal triangle can be defined either by its vertices or its sides.

• Vertices
  • one vertex at the coccyx bone
  • the two ischial tuberosities of the pelvic bone
• Sides
  • perineal membrane (posterior border of perineal membrane forms anterior border of anal triangle)
  • the two sacrotuberous ligaments

Some components of the anal triangle include:^[1]

• Ischioanal fossa
• Anococcygeal body
• Sacrotuberous ligament
• Sacrospinous ligament
• Pudendal nerve
• Internal pudendal artery and internal pudendal vein
• Anal canal
• Muscles
  • Sphincter ani externus muscle
  • Gluteus maximus muscle
  • Obturator internus muscle
  • Levator ani muscle
  • Coccygeus muscle

•  
  Articulations of pelvis. Posterior view.
•  
  The superficial branches of the internal pudendal artery.
•  
  The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx.

• Perineum
• Urogenital triangle

• Anatomy photo:41:01-0202 at the SUNY Downstate Medical Center - "The Female Perineum: Boundaries of the Female Perineum"
• perineum at The Anatomy Lesson by Wesley Norman (Georgetown University) (perineumboundaries)