The straightforward answer is that yes, they do.But there’s more than meets the eye in a dog’s navel!
Alongside all other mammals, dogs do have belly buttons. Medically referred to as an “umbilicus”, the only mammals in fact that do not have umbilici (plural), are marsupials such as the kangaroo and monotremes such as the duck-billed platypus.
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So what exactly is the belly button/umbilicus?
The belly button, or umbilicus as we will now call it, is a residual scar. It represents the remains of where the placenta attached, via the uterus (womb) to the pup, when the pup was a growing and developing foetus inside its mother.
During growth inside the mother’s womb, the placenta was the most vital of organs to the pup, supplying nutrients and oxygen whilst removing waste products. At birth, once the pup is delivered and freed from its amniotic sac (the bag of fluid that surrounds, cushions, and protects the pup), the placenta is redundant and no longer required. The lungs expand and take over the work of oxygen exchange whilst various other developments take place to enable the pup to fend for itself.
The mother will chew off the remnants of the umbilical cord a few centimetres away from the pup’s belly. Over the following few days, the residual stump of cord dries up, contracts, and falls off, leaving behind the small scar of the umbilicus.
And what does it look like?
Many owners may not have examined or noted the presence of the umbilicus in their dog. Typically, they are less obvious on a dog than on a human for several reasons. Most umbilici will be flat and small relative to the size of the dog. Also, usually fur will often grow over them. Occasionally the scar may remain bald, or the hair will fan out from it in, a rosette type pattern.
I’ve heard of umbilical hernias. What exactly are they?
Umbilical hernias are usually easily recognised as a bump or swelling on the lower underbelly of your pup, in the region of the umbilicus (see below). Whilst variably sized (potentially from 1-4cm), they are soft and may also actually fluctuate in size.
A hernia usually develops when the muscles of the abdominal wall do not heal properly. Rather than the muscles fusing together adequately, a variably sized hole remains which acts as a potential gap through which tissues such as fat or intestines may poke through.
A key characteristic is whether a hernia is reducible or not. With a reducible hernia, the bulk of the swelling can be pushed back into the abdomen. A non-reducible hernia, however, indicates that there is a partial obstruction of the hibernating structures, into the opening; so that the hernia remains the same size. The contents of the hernia cannot, therefore, be returned into the abdominal cavity.
If an umbilical hernia is noted, the advice would be to see your vet so that any potential complications associated with the hernia, can be promptly addressed.
And what causes an umbilical hernia?
Both the exact incidence and the cause of umbilical hernias remains unclear.
A sometimes-increased incidence within any one familial line however, does suggest that a genetic predisposition may exist. This can be the case in some purebred lines of certain dog breeds. However, occasionally an umbilical hernia may show up incidentally and as a sporadic finding within an individual pup. These likely ariseas a spontaneous problem during development.
Contention also sometimes exists between vets and breeders in terms of differentiating a true umbilical hernia from a “delayed closure” of the umbilicus.
Whilst with a true hernia, both a “hole” and a palpable ring of tissue are felt, with delayed closure, neither a ring nor hole is felt. It is thought that a small amount of fat or omentum (the double layer of fatty tissue that supports the abdominal organs), slipped through an original hole in the body wall, but that this hole, subsequently closed as far and as well as it could. The small, herniated content is palpable but no hole is felt!
Delayed closure may be a variant of an umbilical hernia or could reflect expression and presence of different genes.
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Occasionally an umbilical hernia will be sustained traumatically.
How big is a hernia likely to be? Does this affect its significance?
The size of an umbilical hernia can vary however the majority are small and