NostrilsThe two openings of the nose, each shaped something like a comma. Air goes in here, or through the mouth.
Nasal cavityThe passage behind the nostrils. Its lining warms and moistens the air and traps dust, and it holds the sense of smell.
PharynxThe throat, crossed by air and food. Air is on its way from the nasal cavity to the larynx, and food to the esophagus.
LarynxThe voice box, at the top of the trachea. A short box of cartilage.
TracheaThe windpipe, from the larynx to the lungs. Rings of cartilage shaped like a U hold it open all the way.
BronchiThe two branches of the trachea, one to each lung. Inside the lung each divides again and again into smaller tubes that end in tiny air sacs.
LungsWhere the blood takes in oxygen and gives up carbon dioxide. A dog's right lung is about a quarter larger than its left.
DiaphragmA sheet of muscle between the chest and the belly. When it tightens, the chest gets larger and air is drawn into the lungs.
The horse 7
NostrilsLarge openings that can flare wide. A horse breathes only through its nostrils; it cannot breathe through its mouth.
Nasal cavityA long passage from the nostrils to the pharynx. It warms and cleans the air on the way in.
Guttural pouchA pouch of air found only in horses and their relatives. One lies on each side, behind the jaw, under the base of the skull.
LarynxThe voice box, at the throat between the pharynx and the trachea.
TracheaThe windpipe. Fifty to sixty rings of cartilage hold it open. At the lungs it divides into the right and left bronchi.
LungsTwo large organs that fill most of the chest. Oxygen passes into the blood here.
DiaphragmA sheet of muscle between the chest and the belly. In the horse it slopes steeply, from under the loin forward and down to the breastbone.
The chicken 9
NostrilOne of the two openings at the base of the beak. Each leads into a short, narrow nasal cavity.
TracheaThe windpipe, a long tube of cartilage rings. The rings keep it from collapsing.
SyrinxThe voice box of a bird. It lies at the lower end of the trachea, where the trachea divides into the two bronchi.
LungSmall and firmly attached to the ribs. It does not swell and shrink like a mammal's; air flows through it in one direction.
Cervical air sacThe air sac at the base of the neck. Air sacs are thin bags that work as bellows: they pump the air, and the lungs stay still.
Clavicular air sacA single air sac in the front of the chest. It lies between the two arms of the wishbone. It is also called the interclavicular sac.
Anterior thoracic air sacThe front air sac of two on each side of the chest. It is also called the cranial thoracic sac.
Posterior thoracic air sacThe rear air sac of two on each side of the chest. It is also called the caudal thoracic sac.
Abdominal air sacA large air sac on each side of the belly. It lies round the organs there. Air from it reaches into the hollow bones of the hip and thigh.
How this list was compiled: Every name checked on 2026-09-30 in two sources. Dog: S. Sisson, The Anatomy of the Domestic Animals (1914, public domain), https://archive.org/details/anatomyofdomesti00siss; the Merck Veterinary Manual's page for dog owners on the lungs and airways; Wikipedia, Respiratory system. Horse: Sisson (1914); the Merck Veterinary Manual's page for horse owners on the lungs and airways; Wikipedia, Equine anatomy, https://en.wikipedia.org/wiki/Equine_anatomy. Chicken: Poultry Extension, Avian Respiratory System, https://poultry.extension.org/articles/poultry-anatomy/avian-respiratory-system/; O. C. Bradley, The Structure of the Fowl (1915, public domain), https://archive.org/details/structureoffowl00brad; Wikipedia, Bird anatomy, Air sac and Syrinx. Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. The horse and the hen keep the outlines of this site's own drawings. Licence: own work
How it works
This dog respiratory system diagram follows the air from the nostrils to the lungs. Two more views show a horse, which breathes only through its nose, and a chicken, which has air sacs and no diaphragm.
Read the full guide
The dog
Air enters at the nostrils and crosses the nasal cavity and the pharynx. It passes the larynx and goes down the trachea, which divides into two bronchi, one for each lung. The diaphragm, behind the lungs, draws the air in.
Horse and chicken
The horse respiratory system diagram has the same parts and adds the guttural pouch. The chicken respiratory system diagram differs: the voice box is the syrinx, the lung is small and stiff, and air sacs pump the air. Press Quiz me to name each part yourself.
A dog's two lungs do not match: the right one is about a quarter larger than the left.
Questions and answers
Do dogs have a diaphragm?
Yes. A dog has a diaphragm, a sheet of muscle between the chest and the belly that draws air into the lungs. Birds have none and move air with their air sacs.
Can a horse breathe through its mouth?
No. A horse can breathe only through its nostrils. Its soft palate shuts the mouth off from the airway except when it swallows.
How many air sacs does a chicken have?
Nine: one clavicular sac, and on each side a cervical, an anterior thoracic, a posterior thoracic and an abdominal sac. Some of them reach into the hollow bones.
What is a syrinx?
The voice box of a bird. It lies at the lower end of the trachea, where the trachea divides into the two bronchi, so a bird's voice comes from deep in its chest.