Veterinary Splanchnology and Applied Anotomy

ANUS

• The anus is the terminal part of the alimentary canal placed below the root of the tail forming a rounded projection with a central depression when contracted
• It is covered externally by thin skin devoid of hair but provided with numerous sweat and sebaceous glands
• It’s lumen, the anal canal is about 5 cm long and is always closed by the contraction of the sphincter muscles and folds of the mucous membrane except during defecation
• The mucous membrane is pale, glandless and covered with thick squamous stratified epithelium
• The muscles of the anus are,
• The sphincter ani internus is the terminal thickening of the circular coat of the bowel and the sphincter ani externus is a broad ring of striped muscle outside the preceding
• The action of both is to close the anus
• The retractor ani is flat striped muscle, which lies between the rectum and the sacro sciatic ligament ending below the preceding
• It reduces the partial prolapse, which the anus undergoes during defecation
• The suspensory ligament of the anus is a band of plain muscle arising from the first coccygeal vertebra, passing down under the retractor, unites with its fellow below the anus
• In the male it is continued as retractor penis muscle. In the female it blends with the constrictor vulvae
• Mucous membrane presents intestinal gland but no villi: solitary glands are numerous.