The bones of the animal’s skeleton vary in shape, size, and structure. Here, this article helps you to identify the types of bones in animals from their skeleton with specific identifying features.
Quick answer: the types of bones in animals are primarily long, short, flat, irregular, and sesamoid. Some animals also have pneumatic bones in their skeleton and visceral bones in different soft organs.
Here, I will focus on the key identifying features of different types of bones from an animal’s skeleton, with examples.
Types of bones in animals
Before going to identify the different types of bones in animals, you might have a strong knowledge of their skeleton. Here, Figure 1 shows the different bones of the cow skeleton (both axial and appendicular parts of the skeleton).
If you notice these bones from this skeleton carefully, you will find the variation in their shape, size, and structure. Most of the animals possess this variation of the bones in their skeleton.
Here, some bones are flattened and possess 2 defined surfaces that cover the specific area of the skeleton. Again, some of the bones are long that possess a cylindrical body and two extremities. These types of long bones primarily occur in the limbs of an animal.
However, let’s see the bones of the joints, especially the carpus and tarsus of the forelimb and hindlimb of the animals, respectively. These are the small-sized bones that possess similar dimensions in length, breadth, and thickness.
There are other smaller or seed-like bones present in the appendicular skeleton (limbs) in animals. These bones develop within the tendon and ossify at birth, which are most commonly found at the caudal aspect of metacarpophalangeal and distal interphalangeal joints.
However, these small, seed-like bones are also seen on the plantar aspect of metatarsophalangeal and distal interphalangeal joints (hindlimb).
Finally, you will find some irregular-shaped bones that are median and unpaired along the long axis of the animals. They possess different bony projections that support the attachment of muscles and ligaments.
Here, Figure 2 shows the different types of bones from the animal’s skeleton that were already described above.
What are the 5 types of bones in animals?
So, from the previous discussion, you may easily understand that there are 5 types of bones in animals –
- Flat bones: flat, irregular bony plate,
- Long bones: hollow cylindrical type,
- Short bones: small pieces of partially smooth surfaces bones,
- Sesamoid bones: small, seed-like bone develops within tendons, and
- Irregular bones: small bones with rough and irregular surfaces,
These 5 types of bones are common in most domestic animals. You may also find the other 2 types of bones mentioned below in the animal’s skeleton –
- Pneumatic bones: long type bones having cavities inside the shaft, and
- Visceral bones: present within the soft tissue of the viscera of some of the animals and birds,
Figure 3 shows the flat, long, short, sesamoid, irregular, pneumatic, and visceral bones of the animals.
Now, I will describe the details osteological features of these bones from the animal skeleton with the diagrams and labeled images.
How many bones are in animals?
Before going to the classification of the bones from the animal skeleton, you may have a good idea of their number. Here, the number of bones in different animals varies according to their body structure. In most of the domestic animals, the number of bones varies from 169 to 298.
Here, Table 1 shows the overview of the number of bones in the skeletons of different domestic animals and birds –
| Species | Cattle | Horse | Dog | Bird |
| Skull bones | 32 | 32 | 50 | 40 |
| Vertebrae | 49-51 | 51-56 | 50 | 40 |
| Ribs, sternum | 27 | 37 | 34 | 18 |
| Forelimb’s bones | 48 | 40 | 90 | 26 |
| Hindlimb’s bones | 46 | 38 | 96 | 42 |
| Visceral bones | 2 | 0 | 1 | 2 |
| Total bones | 204 – 206 | 198 – 203 | 321 | 168 |
The total number of bones in the skeletons of different domestic animals and birds can vary due to fused bones or in their vertebrae.
Description of types of bones in animals
The major 5 types of bones in animals can be easily identified from their skeleton. Here, the features of flat, long, short, sesamoid, and irregular bones from the skeleton are described with labeled images.
Flat bones in animals
The flat bones in animals are relatively thin and expanded in two directions. These bones are irregularly flat bony plates and enclose mostly the cranial and pelvic cavities.
Here, Figure 4 shows the flat bones (frontal bone and hip bone) from the cranial and pelvic cavities of the animals. Again, it also shows the flat bone of the shoulder (Scapula).
These flat bones in the animals consist of the following osteological features –
- They consist of two irregular plates of compact bones (lamina externa and lamina interna),
- Two thin compact plates are separated by the spongy materials, which is known as a dipole.
Examples of flat bones
So, the examples of the flat bones are: cranial and facial bones of the skull, scapula, and bones of the pelvis.
Major functions of the flat bones
The main functions of these flat bones are the protection of vital organs like the brain, heart, lungs, and pelvic viscera. Here, the brain is protected by the cranial bones of the skull, whereas the heart and lungs are protected by the scapula and ribs.
Again, the pelvis viscera are protected by the pelvic bones (ilium, ischium, and pubis). Finally, some of the flat bones in the animal’s skeleton provide sufficient area for the attachment of the muscles.
Long bones in animals
The long bones in animals are typically of elongated cylindrical form with enlarged extremities. These types of bones occur in the limbs of animals, where they act as the supporting column and the levers.
The key osteological features of the animal’s long bones are –
- The cylindrical part of the long bone is the shaft or body, which encloses the medullary cavity,
- Two expanded or enlarge extremities are the proximal and distal,
- Most of the bones ossify in cartilage,
The cylindrical shaft of the long bone is also known as the diaphysis. Again, the two extremties is the epiphysis, which also consists of the metaphysis between each epiphysis and the diaphysis.
Here, Figure 5 shows the long bones from the forelimb and hindlimb of the animal skeleton.
Examples and classification of the long bones in animals
The best examples of the long bones are in the extremities of the skeleton or body –
- Long bones in thoracic limbs: humerus, radius, ulna, metacarpals, phalanges, and
- Long bones in pelvic limbs: femur, tibia, fibula, metatarsals, and phalanges,
The long bones in different animals can be classified into modified long bones and miniature long bones.
Modified long bones: these bones possess the features of the long bones; they have the body and extremities. But, they do not possess the medullary cavity, and thus they are termed as the modified long bones.
Examples of modified long bones: the clavicle in dogs, rabbits, and birds is a modified long bone.
Miniature long bones: these bones have a shaft, two extremities, and other osteological features like the long bones. But, they are very small in some of the animals, and thus they are termed as the miniature long bones.
Examples of the miniature long bones: metacarpals and metatarsals are the miniature long bones in dogs and cats.
Here, Figure 6 shows the modified long bone (clavicle) and miniature long bones (metatarsals) of the different animals.
Short bones in the animal’s skeleton
These are the small pieces of bone mainly found in the complex joints of the animal skeleton, such as in the carpus and tarsus. The main identifying features of the short bones in the animal’s skeleton are –
- They are cuboid or approximately equal in dimension (length, breadth, and thickness),
- There is no single marrow cavity in the short bones.
- But the interior of these bones consists of spongy bone filled with marrow space,
- The exterior of these bones consists of a thin layer of compact bone,
- Most of the short bones possess six smooth surfaces,
Here, Figure 7 shows the short bones from the carpus (knee) and tarsus (hock) joint of the animal’s limbs.
Examples of short bones in animals
- Short bones of carpus: radial, intermediate, ulnar, accessory, second, and third are fused, and the fourth carpal bone.
- Short bones of the tarsus: talus, calcaneus, fourth and central fused, first, second, and third fused tarsal bones,
The main function of the animal’s short bone appears to be that of diffusing concussion.
Sesamoid bones in animals
Sometimes, the sesamoid bones in animals are also grouped under the short bones. They are called sesamoid bones due to their resemblance to a sesame seed.
Although many of the sesamoid bones of the domestic animals are un-sesamelike shape. The gross identifying features of the animal’s sesamoid bones are –
- Small sesame (seed) like bones develop within the joint capsule or tendon,
- You will not find any periosteum and haversian system in the sesamoid bones.
Figure 8 shows the larger sesamoid (patella), proximal sesamoid, and distal sesamoid bones from the animal’s limb.
Examples and functions of animals’ sesamoid bones
- Larger sesamoid bone: the patella, which is located in the stifle joint,
- Proximal sesamoid bones: 4 in number in each limb, 2 for each developed digit (for cattle),
- Distal sesamoid bones: 2 in number in each limb, 1 for each developed digit (for cattle),
The animal’s sesamoids reduce the friction, increase leverage, and change the direction of the tendon.
Irregular bones in animals
Irregular bones are unpaired on the median plane of the animal’s body. They are considered specialized types of bones in animals.
Let’s see the unique osteological features of the irregular bones in animals from their skeletons –
- They are small bones with rough and irregular surfaces placed in the midline of the skeleton,
- They feature prominent projections or processes,
Here, Figure 9 shows the irregular bones from the animal skeleton.
Examples of irregular bones in animals
- Bones of the animal’s vertebrae (cervical, thoracic, lumbar, sacral, coccygeal), and
- Unpaired bones of the animal’s skull,
The functions of the irregular bones are various and offer support, protection, and muscular attachment.
Pneumatic bones in animals
Pneumatic bones of the animals and birds contain the air space or sinuses that communicate with the environment. These bones are responsible for making the body light and help in flying in birds.
Examples of pneumatic bones: the frontal, maxillary, and ethmoid bones are pneumatic bones of the animals. Again, most of the long bones and a few fused bones in birds are also pneumatic type bones.
Here, Figure 10 shows the major pneumatic bones from both animals and birds’ skeletons.
Visceral bones in animals
These are the special type of bones in an animal’s body. These bones are located in the soft tissue of the different visceral organs. They were not considered part of the bones of the skeleton.
Examples of visceral bones:os cordis of the ox, os opticus in birds, os rostate in pigs, and os phrenic in camels.
Figure 11 shows the os cordis bones of the ox heart.
How to identify animal bones?
To identify the animal bones, you might have the following –
- Good knowledge of the animal’s skeleton (parts, orientation, and others),
- Must know the names of the bones from the axial and appendicular skeleton,
- Vast knowledge of the unique osteological features of the specific bone,
- Might have knowledge on the location, type, and direction of the specific bones of the skeleton,
If you acquire this knowledge practically, then you will easily identify the animal bones from their skeleton. But make sure you have a good knowledge of the variation of the bones from different animal species.
Figure 12 shows the key identifying features of the animal bones from its skeleton.
Conclusion
So, the long, short, flat, irregular, and sesamoid are the five major types of bones in animals. But, based on the animals, you will also find the pneumatic and visceral bones in their skeleton and soft organs, respectively.
The key identifying osteological features of these types of bones might help you to identify them in their skeleton easily.
References
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- Rowen D. Frandson, W. Lee Wilke, and A. Dee: Anatomy and physiology of farm animals, 4th edn.Wiley-Blackwell, USA.
- Best Adam et al., Anatomy, histology, development and functions of ossa cordis, Anatomia, histologia, embryologia, 2022.
- Getty, R,. Sission and Grossman’s The anatomy of the domestic animals, 5th Edn. W. B. Saynders and Co. Philadelphia (USA).
- Nickel, R. Schummer, A. and Seiferle, E.: The anatomy of domestic animals, 1st Edn. Verlag Paul Parey, Berlin.
- Larsen et al., 2023. Navicular bone fracture and severe deep digital flexor tendinopathy after palmar digital neurectomy in two horses. Open Veterinary Journal, 13 (12).
- Hermanson et al., Miller and Evan’s Anatomy of the dog, 5th Edn. Elsevier.
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