Dictionary > Rhinarium

Rhinarium

rhinarium definition and example

Rhinarium
n., plural: rhinaria
[raɪnərɪəm]
Definition: The hairless skin area surrounding the nostrils in some mammals

Rhinarium Definition

Rhinarium is the hairless (furless) skin area around the external openings of the nostrils in many mammals. This surface of the skin is usually more or less moist, crackled, or embossed. The rhinarium is part of the olfactory system and is therefore associated with the sense of smell (olfaction).

Word origin: The term rhinarium is a Latin word, meaning “belonging to the nose”
Synonym: nose leather; nosepad; “truffle”; wet snout; wet nose; planum nasale

Structure of Rhinarium

canine rhinarium parts
Rhinarium’s structure of a dog (toy poodle) showing philtrum (midline groove or cleft on the rhinarium). Image Source: Maria Victoria Gonzaga of Biology Online.  Photo: @dracarys_diary (IG)

Rhinarium is the part of the nose that has a naked surface, meaning it has no fur but glabrous skin. It has wrinkles on the surface (called crenellations). It surrounds the nares (nostrils where gases are exchanged through the nasal passages — also called nasal cavities).

Most mammals have a groove called a philtrum. In many species with rhinarium, it is located posteriorly, in the middle of the rhinarium to the upper lip.

Watch this vid: why dogs have wet noses…

 

Functions of Rhinarium

The rhinarium is believed to be involved in the olfactory function (smelling) as many animals with rhinarium are characterized to have a greater acute sense of smell. In many species, olfaction (sense of smell) is carried out by the main olfactory system and an accessory olfactory system. The question is, which part of the olfactory system does the rhinarium belong to? Is it part of the main olfactory system that detects airborne substances or is it part of the accessory olfactory system that detects chemicals dissolved in fluids? The answer remains inconclusive.

Some claims that the rhinarium is a continuation (extension) of the olfactory epithelium (of the main olfactory system). Others believe that rhinarium is sensitive to pheromones and therefore associated with the vomeronasal organ (VNO) that detects liquid organic compounds like pheromones. The VNO is part of the accessory olfactory system that is connected to the philtrum via ducts inside the mouth. It is believed that the nonvolatile odorants may have been conveyed from the rhinarium to the VNO through the philtrum.

Rhinarium serves other purposes in certain animals. In walruses, the rhinarium is covered with bristles that protect, primarily when the walrus forages for shellfish.

The rhinarium also enables wind direction detection. Animals with rhinarium detect smell and identify the direction where the odor is coming from.

Examples of Rhinarium

Examples of mammals that have rhinarium include cows, cats, dogs, elephants, and walruses. Some primates also have a rhinarium. The strepsirrhines (i.e. lemurs, lorises, pottos, and galagos) are an example. Their primitive rhinarium is a feature that characterizes them. Strepsirrhines belong to the suborder Strepsirrhini (or Strepsirhini) of the order Primates. They are also referred to as wet-nosed primates. Other species of Primates lack “wet noses”. They are referred to as dry-nosed primates. They belong to the suborder, Haplorrhini (haplorrhines).

Frequently Asked Questions on Rhinarium

  • Where is rhinarium found? Rhinarium is at the mammalian nose tip that has no hair or fur.
  • Which primates have a rhinarium? Strepsirrhines (suborder Strepsirhini) are examples of primates with wet rhinarium. They include the lemurs, galagos, lorises, and galagos.
  • Do humans have a rhinarium? No. Humans do not have a rhinarium. Humans descended from the lineage of primates that have “dry noses” — the haplorhines of the suborder Haplorhini. Humans do have a philtrum, though, which is a vestigial structure as it has no clear function. The human philtrum is bordered by ridges and typically a depression (not a cleft) below the nose. A medical condition where the philtrum fails to form/fuse during embryonic development is called a “cleft lip”. In other conditions wherein the philtrum is smooth or flattened, this could be a symptom of fetal alcohol syndrome or Prader-Willi syndrome.

Take the Quiz on Rhinarium!

Quiz

Choose the best answer. 

1. What is rhinarium?

2. The cleft in the rhinarium is called ...

3. The function of rhinarium

4. Which of these animals have a rhinarium?

5. Which of the following is true about strepsirrhines?

Send Your Results (Optional)

Your Name
To Email

 

References

1 Dijkgraaf, S., Zandee, D. I., Addink, A. D. F. eds. (1978). Vergelijkende dierfysiologie (Comparative animal physiology) (in Dutch) (2nd ed.). Utrecht: Bohn, Scheltema & Holkema.

 

©BiologyOnline.com. Content provided and moderated by Biology Online Editors.


You will also like...

New Zealand - Biodiversity fauna
New Zealand’s Biodiversity

Find out more about New Zealand's unique biodiversity by exploring a range of different ecosystems and the key role of s..

Sugar Homeostasis
Sugar Homeostasis

The blood sugar level is regulated by two hormones. The mechanism behind this type of negative feedback control is descr..

Evolution of Life - Ancient Earth
Evolution of Life – Ancient Earth

Autotrophs flourished, absorbing carbon and light. Soon after, primitive life forms that could assimilate oxygen thrived..

green leaf - close up view
Leaves

Leaves are the major photosynthetic organ of a plant. Apart from that, they are also crucial to water movement. In this ..

An artistic depiction of a human embryo
Growth and Development of a Human Baby

Upon fertilization, a zygote forms and develops into an embryo. This tutorial elaborates on the growth and development f..

Chromosomes X and Y and Sex Determination
Chromosomes X and Y and Sex Determination

This tutorial looks at sex determination via the sex chromosomes, X and Y. Read it to get more info on X and Y chromosom..

Related Articles...

No related articles found

See all Related Topics