The ribs of a dog form the most significant part of the thoracic skeleton. They arrange serially and intersperse by the intercostal spaces. The veterinary student and dog owner have a common question on how many ribs do dogs have. Here, I will provide detailed information on the number of dog ribs with their anatomy.
You will find thirteen pairs of ribs in the thoracic skeleton of a dog. The exact number of ribs find in a ruminant’s skeleton, but the structure may vary slightly. I will also show you the anatomical variation of dog ribs compared to other animals at the end of this article.
If you want to know the detailed anatomy of these thirteen pairs of ribs from a dog, you may continue this article till the end.
How many ribs do dogs have
So, first, you should know – how many ribs do dogs have. There are usually thirteen pairs of ribs (total twenty-six) in a dog skeleton. Each dog rib consists of a bony dorsal part and a cartilaginous ventral part that meets the chondrosternal junction.
A dorsal bony part – it is caudolaterally convex and also known as the os costale, and
The ventral part – is costal cartilage and is also known as cartilage costalis.
The dorsal parts of the dog ribs articulate with the thoracic vertebrae. Again the ventral aspect of the ribs differs in their articulation with the sternum of a dog.
The Paris of ribs corresponds in number to the thoracic vertebrae in any animal. You will find the following pairs of ribs in different animals compared to a dog –
- Dog – usually thirteen pairs of ribs (may vary in species)
- Ruminant (cow, sheep, goat) – thirteen pairs of ribs
- Pig – the skeleton of pig consists of thirteen to fifteen pairs of ribs
- Horse – usually eighteen pairs of ribs
How to count ribs in a live dog?
Do you know the counting process of ribs from a live dog or other animals? This is a straightforward process to count the number of ribs from a dog or other animals.
First, you might identify the thoracic cavity of a dog. I hope you will do it so quickly and could demark the thoracic cavity from the abdominal cavity.
The thoracic outlet of the dog thoracic cavity bounds with the last ribs laterally. So, you will find the last ribs by a surface approach that helps you demark the thoracic cavity from the abdominal cavity. In a live dog, you might count the ribs from the last. So, the last one is the number thirteen ribs in a dog. Thus you might go forward and count the rest ribs as well.
I hope you can count the ribs from a live dog now. And you will get your answer to the question – how many ribs do dogs have practically.
The boundary of the thoracic cavity of a dog
As a veterinary student, you might have a clear concept of the boundary of a thoracic cavity of a dog. Here, I will provide a little and basic information about the boundary of a thoracic cavity of a dog.
The dog thoracic cavity is a laterally compressed cone-shaped cavity with an oblique and concave base that directs caudally. The cranial cone is the thoracic inlet. Let us discuss the boundary of the thoracic inlet of a dog.
The thoracic inlet is an ova; opening that forms by the first thoracic vertebrae, the first pair of ribs, and the cranial end of the sternum. Again, the base of the dog thoracic inlet forms by the diaphragm. The lateral wall of the dog thoracic inlet forms by the ribs and thoracic muscles.
In addition, the roof of the thoracic inlet of a dog forms by the thoracic vertebrae, proximal end of the ribs, and muscles. The sternum, distal end of the costal cartilage, and few muscles form the floor of the dog thoracic cavity. Again, the wall, roof, and floor cover the skin and subcutaneous tissue externally.
The dog thoracic outlet also forms by the last thoracic vertebrae (dorsally), muscles and last segment of the sternum (ventrally), and last pairs of ribs (laterally).
Types of ribs in a dog thoracic skeleton
If you notice the thoracic skeleton of the dog, you will find three different types of ribs. Some of them directly articulate with the dog’s sternum, and others indirectly join with the sternum. Again, the last Paris of a rib of a dog skeleton has no articulation with the sternum. So, you may ask me how many and what type of ribs do dogs have.
Usually, you will find three types of ribs in the thoracic skeleton of a dog –
The true ribs – ideally, the first nine pairs of ribs articulate directly with the sternum of a dog. Therefore they are the sternal or true ribs in the thoracic skeleton of a dog.
The asternal ribs – the remaining caudal ribs of the dog articulate indirectly with the dog sternum by joining with the cartilage of the rib in the forms of a costal arch. So, you will find the costal arch in both lateral aspects of dog’s thoracic cavity.
At the end of the series, a floating rib- ribs, that cartilage ends free in the musculature without attachment to adjacent cartilage. In dog and cat, the last pair of ribs are always floating.
The nine ribs of the dog skeleton are the longest rib. You will also find the longest costal cartilage in the nine ribs of a dog. The dorsal and cartilaginous parts of the other ribs of a dog become progressively shorter than that of the nine ribs.
The costochondral junction of the third to eight ribs lies nearly the same horizontal plane of the body. You will find a total of twelve intercostal spaces in the thoracic wall of a dog.
The space between the adjacent ribs of a dog is known as the intercostal space or spatium intercostale.
Dog rib cage anatomy
Now, I will go with dog rib cage anatomy in this part of the article. It consists of the body of thoracic vertebrae, all thirteen pairs of ribs, sternum, and some of a dog’s vital organs.
In my previous article, you will get detailed information about the different parts of a typical vertebra (including the body). Again, I will not repeat the same facts on the body of a dog vertebrae. You already know how many ribs do dogs have. Let’s talk about all thirteen pairs of ribs from the dog thoracic skeleton.
In a typical rib of a dog, you will find the following components –
- A vertebral extremity
- An intermediate shaft or body, and
- A sternal extremity
Let’s discuss these components of the dog ribs.
A vertebral extremity of dog ribs
The vertebral extremity of the dog ribs possesses a round head, a distinct neck, and a tubercle. In the head of the dog ribs, you will find the cranial and caudal articular facets. These facets articulate with the socket that forms by the cranial and caudal costal fovea on the bodies of the two adjacent vertebrae.
The articular rib surfaces corresponding to those of the vertebrae are of approximately equal size and convex. They face cranially and caudally and separate by a transverse ridge to attach the interarticular ligament of the rib’s head.
At the level of the first to tenth thoracic vertebral region, the head of each rib articulate over the intervertebral disc with the costal fovea. This structure forms by parapophyses of adjacent vertebrae.
Again, at the eleventh or twelfth thoracic vertebrae level, the caudal pair of costal fovea disappear as the last two or three ribs articulate only with their corresponding vertebrae.
The transverse ridge on the articular surfaces of the ribs head modifies gradually. You will not find any distinct transverse ridge on the head articular surfaces of the ribs.
The head joins to the intermediate body of the dog ribs by a distinct neck. Do you know how many tubercles do dogs have on the neck of their ribs? The tubercle of the dog rib contains only one tubercle at the junction of the intermediate body.
In addition, the costal tubercle possesses a facet for articulation with the transverse process of the same vertebrae of a dog. Since the necks of the dog ribs become gradually shorter caudally, the articular facet of the head and tubercle grow closer till they become confluent. This will give you the results in an increased movability of the last few pairs of dog ribs.
An intermediate body of dog ribs
The intermediate body of the dog ribs si distal to the costal tubercle. In general, the dog ribs are cylindrical and slightly enlarged at the chondrosternal junction. The third, fourth, and fifth ribs show some lateral compression of the distal halves of the bony parts.
The body of the dog ribs is more curved than the ribs of the other domestic animals. In addition, the length of the ribs gradually increases in the first ten ribs to become progressively shorter caudal to it. Usually, the cranial surface of the rib’s body is flat, and the caudal surface remains round.
A dog’s first six or eight ribs are the widest, and the ninth ribs are the longest. While the width gradually decreases from the cranial to caudal, the thickness of the ribs increases.
You might find a significant variation in the shape and size of the ribs in the different breeds of dogs. In the large breed of dog, the ribs are flatter than they are in the small species. In all the breed of dog, the vertebral part of the ribs is slightly thicker than from lateral to medial than they are from cranial to caudal.
The region where the intermediate body of dog ribs bent more strongly is known as the costal angle. Its surface and border provide attachment to the muscle of the trunk, especially to the respiratory musculature.
You will find a costal groove at the dog ribs’ caudal margin that protects the intercostal vessels and spinal nerve.
A sternal extremity of dog ribs anatomy
The dog ribs’ distal extremity (sternal) articulates with the costal cartilage that forms the costochondral junction. In addition, the costal cartilage is the cartilaginous cylindrical structure in a dog. It is smaller in diameter than the bony ribs in a dog.
Near the costochondral junction, this costal cartilage inclines cranially. You will find a typical incline costal cartilage in the first and twelfth ribs of a dog.
The end of the costal cartilage of the dog sternal rib is cylindrical. It articulates with the sternum of a dog.
Each pair of ribs joins the sternum between the successive sternal segments of the dog sternum.
The first pair of the dog rib articulates with the first sternebra of the sternum (manubrium sterni). They were succeeding in true ribs cartilage articulate with the successive intervertebral cartilage.
In addition, the eighth and ninth costal cartilage articulates with the cartilage between the seventh sternebra and last sternebra (xiphoid cartilage of sternum). Again, the costal cartilage of the tenth, eleventh, and twelfth ribs are long, slender rods that join to the one above by connective tissue and form the costal arch.
But, you will find a most shorter and rudimentary costal cartilage in the thirteen ribs of a dog. It enters into the musculature of the flanks, in which it terminates.
How many segments do dogs have in the sternum and ribs?
Do you know how many segments do dogs have in their sternum for articulation with ribs? The sternum of a dog is an unpaired bone that forms the ventral boundary of the thorax. Typically, you will find eight segments (sternebrae) in the dog sternum. The individual segment of sternum fuse, with ossification.
The sternal end of the ribs articulates with the intervertebral cartilage, except the first pair that communicates with the first sternebrae.
In a dog, the first and the last sternebrae are specialized. The cranial half of the first sternebrae (manubrium) expands and bears lateral projection to attach the first costal cartilage. It is longer than the other segments of the dog sternum.
“The dorsolateral margin of the dog sternum posses a series of notches that receive the costal cartilage of the sternal ribs for articulation.”
The last segment of the dog sternum (xiphoid process) is flat and wide. Its length is approximately three times its width. The xiphoid cartilage of the dog sternum si roughly triangular and posses an oval foramen in its caudal half.
You will find a thin cartilaginous plate at the caudal end of the xiphoid process of a dog sternum. The cartilaginous joints between the sternebrae may ossify in the older dog.
Contents of the dog rib cage anatomy
You will find the more vital organs in the dog rib cage anatomy. Following are the contents that you will find in the dog rib cage –
- The lung and heart of a dog
- A thoracic part of the dog esophagus and trachea
- Beginning of the large vessels, lymph nodes, nerves
“You might know the different body cavities of a dog with their contents.”
You may read other articles related to dog anatomy from anatomy learner
- Dog skeleton anatomy labeled diagram
- Anatomy of dog skull with diagram
To get more updated labeled diagrams on the dog rib cage, you may follow anatomylearner on social media.
How many ribs do other animals have to compare to dogs?
You already got an idea about the number of ribs in other animals that I provided at the article’s beginning. But, now I would like to provide more information – how many ribs do other animals have compared to dogs.
There are eighteen pairs of ribs present in horse, ut of which the first eight pairs are sternal, and the rest ten pairs are asternal ribs. You will find maximum width in the sixth ribs and maximum length in the eleventh ribs.
The curvature of the body of a horse rib gradually increases up to the eleventh rib. Again, the intermediate body of the horse ribs is less width and less flat than that of an ox.
In a rabbit, you will find twelve to fourteen pairs of ribs which seven pairs are sternal and the remaining five to six pairs are asternal. All the ribs excepting the last four, have a prominent head and articular process.
In the pig, you will find a variation in the number of ribs. There are fourteen to fifteen pairs of ribs present in the pig thoracic skeleton. The seven pairs are sternal, and the remaining seven to eight pairs of ribs are asternal in a rabbit skeleton anatomy.
There are seven pairs of ribs present in the chicken skeleton anatomy. You will find exceptional osteological features in the chicken ribs.
Each rib has a dorsal and a ventral segment. The first two ribs do not extend up to the sternum. Each of the dorsal element of the second to sixth ribs of a chicken possesses a caudal extension (uncinate process) that support the thoracic cage.
Sternum segments in other animals compared to a pig.
You know there are eight sternebrae present in the sternum of a dog. But this number may vary in different species of animals. In ruminant, you will find seven sternebrae in their sternum. In the horse sternum, you will also find seven sternebrae.
The horse sternum is boat-shaped and compressed laterally towards the cranial end and dorsoventrally at the caudal end. Ventrally the horse sternum presents a prominent crest. You will also find a cranial cartilaginous extension in the manubrium sterni of the horse sternum.
You will also find seven segments in the sternum of a rabbit. The first segment is long and articulate, with the clavicle on either slide of a rabbit.
But in a pig, you will find six segments in the sternum that fused. The manubrium sterni is elongated and compressed from side to side. Again, the xiphoid process is long, and the xiphoid cartilage is small in a pig sternum.
Frequently asked questions on dog ribs anatomy.
Now, I will try to solve the most common question on dog ribs cage anatomy. You will also find the other related question on the ribs of other animals.
What type of skeleton does a dog have?
The dog has both axial and appendicular skeleton like a cow has. The axial skeleton consists of a skull, all segments of vertebrae, ribs, and sternum. Again, the appendicular structure of a dog includes the bones from the hind and forelimbs.
What animal has 12 ribs?
In the whale, you may find six pairs of ribs (total twelve in number).
Does the dog have an extra rib?
What animal has 14 ribs?
In chicken and most bird species, you will find seven pairs of ribs (total fourteen in number).
Okay, how many ribs do dogs and cats have?
Both the dog and cat have thirteen pairs of ribs in their thoracic skeleton. The first nine pairs are sternal ribs that directly attaché to the sternum. And the rest four pairs of ribs are asternal in both dog and cat. in addition, the last pair of ribs is always floating ribs in both dog and cat.
How many ribs do dogs have on each side?
If you notice in the dog rib cage anatomy, you will find thirteen ribs present on each side.
How many floating ribs do dogs have?
Generally, you will find the only one floating rib in a dog skeleton anatomy. The last rib pair is floating ribs in the dog skeleton that do not articulate with the sternum.
Conclusion
I hope you got the best answer to your inquiry – how many ribs do dogs have. Thirteen pairs of ribs are present, of which nine are sternal, and four are asternal in a dog skeleton anatomy. I also think the labeled diagram of the dog rib cage was helpful for you. The ribs of a dog thoracic skeleton were strongly curved, narrow, and thick. In addition, the first eight or nine ribs of the dog thoracic cage increase in width in their ventral part.
The last pairs of ribs of the dog’s thoracic skeleton were floating. Again, the head of a dog’s last two or three ribs articulates with only one vertebra. You will find long costal cartilage that curves cranially and caudally at the distal extremity of dog ribs.
