If you love dogs, whether as pets or for security, it’s hard not to be fascinated by their physical capabilities. From running at incredible speed to jumping at outrageous heights, their physical traits might leave you thinking that dogs don’t have bones at all. But how many bones does a dog have? Continue reading to find out.
How Many Bones Does a Dog Have?
Since dogs are vertebrates, they have a skeletal system that comprises different types of bones. The skeletal system forms the structural foundation for the dog and protects the dog’s body tissues and internal organs. It is the framework that supports the entire body.
Bones are made of minerals like calcium and phosphorus that form a mineral known as calcium phosphate. This mineral strengthens and hardens the scaffolding to help it withstand excess pressure and stress. Bones also have a substance called collagen, which combines with calcium to make them stronger and more flexible.
Every bone in a dog’s body plays a vital role. For instance, the skull protects the brain and the eyes, while the ribcage protects internal organs like the lungs, heart, liver, etc. Bones in the legs enable the dog to stand, walk, and run. Although each bone has a specific function, the most important ones are those that support the entire body and protect internal organs.
The number of bones in a dog depends on the dog’s breed. Since bones are the blocks that form an animal’s physical structure and profile, they come in different sizes, shapes, and designs. A dog’s structure is made of long, short, irregular, sesamoid, and flat bones.
Although different dog breeds have a varying number of bones, the overall number of bones in a dog’s skeletal system is 321 bones. These bones are categorized by their location in the dog’s skeletal system. Here are the various categories of bones in a dog:
- Vertebral column – 50 bones
- Skull and hyoid bones – 50 bones
- Ribs and sternum – 34 bones
- The thoracic limb – 90 bones
- The pelvic limb – 96 bones
- Heterotopic skeleton (baculum) – 1 bone
Please note that these categories are further subdivided into smaller categories. Here is a detailed outline of the subdivisions and the number of bones that each subcategory carries.
The vertebral column is the backbone or spine, which forms the axial skeleton. The vertebral column is the main trait that defines vertebrates. Its notochord (flexible shaft of identical composition), which is present in every chordate, has been substituted with a segmented sequence of bone (vertebrate) which is divided by intervertebral discs.
Each vertebrate is named according to its region and position, and it can be used as an anatomical landmark that can guide intrusive procedures like lumbar punctures. This column forms the spinal canal – a void that holds and guards the spinal cord.
A dog’s vertebral column consists of approximately 50 irregular bones. These bones are further subdivided into five categories, including:
- Cervical vertebrae – 7 bones
- Thoracic vertebrae – 13 bones
- Lumbar vertebrae – 7 bones
- Sacral or sacrum – 3 bones
- Caudal vertebrae – 19 to 20 bones
Skull and Hyoid
The skull is a cavity made of several bones to hold and protect the brain and other organs like eyes and ears. This cavity comprises four types of bones: cranial bones, ear ossicles, hyoid, and facial bones. The cranium and mandible parts of the skull are the most prominent.
The skull is the anterior-most part of the overall skeletal system of any vertebrate and is a product of cephalization. The main roles of a skull include holding and protecting the brain, fixing the space between the eyes for stereoscopic vision, and fixing the location of the ears for the localization of the distance and direction of the sound.
The hyoid bone connects the skull and the postcranial skeleton. It’s located in the neck and can be felt right above the thyroid cartilage. The number of the skull and hyoid bones in dogs varies from 36 to 50, depending on the dog’s breed. These bones give the dog its facial structure and are subdivided into two categories: facial bones and cranium bones
- Occipital, basioccipital bones, supraoccipital bones
- Frontal bone
- Parietal and interparietal bones
- The sphenoid bone (presphenoid and basisphenoid)
- A temporal bone
- The ethmoid bone
- The nasal bone
- Maxilla bone
- Mandible bone
- Incisive bones
- Lacrimal, pterygoid, and vomer bones
- Dorsal and ventral concha
- Zygomatic and palatine bones
The thoracic limbs are bones that form the middle section of the vertebral column in the space between the lumbar vertebrae and cervical vertebrae. A dog has 13 thoracic vertebrae that form its mid back (thoracic spine). These vertebrae have a total of 90 bones that enable the dog to move comfortably.
A dog has two thoracic limbs that have 45 bones each. Here are the subcategories of a dog’s thoracic vertebrae:
- The arm or brachium bone, which is the humerus of a dog
- The scapula, clavicle, and coracoid bones (bones of the shoulder girdles)
- Forearm or antebrachium bones (radial and ulna bones)
- Carpal, metacarpal, and phalanges (bones of the manus)
- The thoracic limb, which has proximal sesamoid and distal sesamoid bones
Ribs and Sternum
Dogs have 13 ribs (9 sternal, 4 asternal). These are the bones that form the rib cage. They surround the dog’s chest, allowing its lungs to expand for comfortable breathing.
Ribs also protect vital organs like the lungs, heart, and thorax. The sternal ribs (real ribs) are connected to the sternum, while the asternal ribs (false ribs) are connected to the sternum indirectly through the cartilage of the rib to form a costa arch. In total, a dog has 34 ribs and sternum bones.
Pelvic limbs bear the dog’s 40 to 45 percent of its weight and give it most of the thrust for movement. The pelvic limbs are made of two main parts: the femur and the stifle or knee. The femur is part of a dog’s leg located above the knee on its hind legs. The stifle/knee, on the other hand, is the joint located in the front of a dog’s hind leg aligned with the stomach.
Pelvic limbs are similar to thoracic limbs, and they come in pairs of 48 bones each. Here are the bones that form a dog’s pelvic limb:
- The thigh bone (the femur)
- Os coxae bones (ilium, ischium, and pubis)
- The leg bones (tibial and fibula bones)
- Large sesamoid bone, which is the patella of the stifle joint
- The pelvic limb, which contains proximal and distal sesamoid bones
- Tarsal, metatarsal, and phalanges (bones of the hind’s paw)
Also known as L1 to L5, lumbar vertebrae are the largest bones in an animal’s spine. They form the dog’s lower back below the thoracic vertebrae. A dog has 7 lumbar vertebrae. These vertebrae are more identical and longer in appearance than thoracic vertebrae. Another major difference between lumbar vertebrae and thoracic vertebrae is the fact that the former lack costal facets.
The main purpose of the lumbar spine is to keep the entire spine flexible and allow it to extend. However, this flexibility is limited at the L4 to L5 vertebrae because of the intertransverse joints.
Heterotopic Skeleton (baculum)
The heterotopic skeleton is an extraskeletal bone found in the penis of several species of mammals like carnivores, rodents, primates, and insectivores, among others. This bone forms through ossification in connective tissue. It grows rapidly during puberty.