Changes

*The dog and cat posses two '''anal sacs'''. In the dog, these are the size of a hazlenut.

*The dog and cat posses two '''anal sacs'''. In the dog, these are the size of a hazlenut.

**Located ventrolaterally between the internal and external anal sphincters.

**Located ventrolaterally between the internal and external anal sphincters.

**Large, coiled apocrine tubules that have many tubuloalveolar glands that produce a fatty secretion in their walls.

**They are large, coiled apocrine tubules that have many tubuloalveolar glands in their walls.

***These tubuloalveolar glandsw produce a fatty secretion.

**The fundus of the sac secretes a potent smelling fluid that drains through a single duct to an opening near the anocutaneous juncntion.

**The fundus of the sac secretes a potent smelling fluid that drains through a single duct to an opening near the anocutaneous juncntion.

**The anal sacs get compressed during defecation, which causes the fluid to be expressed. The scent of the fluid is thought to act as a territorial marker.

**The anal sacs get compressed during defecation, which causes the fluid to be expressed. The scent of the fluid is thought to act as a territorial marker.

***Anal sacs are clinically important as they are commonly diseased in dogs - frequently, they become enlarged due to accumulated secretion.

***Anal sacs are clinically important as they are commonly diseased in dogs - frequently, they become enlarged due to accumulated secretion.

*The '''dog''' has '''perianal glands''' that lie in the skin surrounding the anus.

*The '''dog''' has '''perianal glands''' that lie in the skin surrounding the anus.

**They are modified sebaceous glands.

**They are modified sebaceous glands.