The cow metacarpal bones form the middle sub-segment of the manus of the forelimb. In this guide, I will help you to learn and identify the osteological features of cow metacarpals with labelled diagrams.
Quick answer: the large metacarpal of a cow is a long, fused bone of the third and fourth metacarpals. Again, the small metacarpal is an ill-developed bone situated at postero lateral aspect of the large metacarpal.
I will also show you how to differentiate the cow’s metacarpal from other species like horses and dogs. You will also know the technique to identify the right/left metacarpals from the cow’s forelimb.
Cow metacarpal
The cow’s metacarpal bones consist of a large metacarpal and a small metacarpal. These bones are considered the long bones of the forelimb of the cow skeleton.
Together, the large and small metacarpals form the middle sub-segment of the manus. Again, you know the manus is the last segment of the forelimb, which consists of the carpus, metacarpus, and digits.
Here, Figure 1 shows the large and small metacarpal bones along with the different segments of the cow’s forelimb. It also shows the three different sub-segments of the cow’s manus.
What is the carpus in a cow?
Carpus is the sub-segment of the manus segment of the forelimb that consists of six carpal bones.
What is the metacarpus in a cow?
Well, the metacarpus is the second/ middle sub-segment of the manus segment of the forelimb that consists of large and small metacarpal bones.
Now, I will describe the osteological features of the cow’s large and small metacarpal bones separately with diagrams.
Large metacarpal bone in a cow
The number of developed metacarpal bones varies in different animal species. In a cow, you will find two developed metacarpals, whereas a horse has only one, and a dog has five metacarpals.
Here, Figure 2 shows the number of developed and underdeveloped metacarpals in cows, horses, and dogs.
But these two developed metacarpals (III and IV) in the cow fused to form a single, large metacarpal bone. Here, metacarpal III is medial in position, whereas metacarpal IV is lateral in position.
Again, the cow’s small metacarpal represents the metacarpal V, which is attached at postero lateral to the metacarpal IV.
- Thus, the cow’s large metacarpal = fusion of Metacarpal III + Metacarpal IV,
- And cow’s small metacarpal = Metacarpal V.
Here, Figure 3 shows the fusion of the metacarpal III and Metacarpal IV in the cow’s metacarpus sub-segment.
The cow’s large metacarpal bone is placed vertically between the carpus proximally and the fetlock joint distally. As a long bone, this large metacarpal also possesses a shaft/body and two defined extremities: proximal and distal.
Here, Figure 4 shows the location, body, and two extremities of the cow’s large metacarpal from the forelimb.
Cow’s large metacarpal bone identification
It will be great if you identify all the osteological features of the cow’s large metacarpal bone first. That will help you to describe this large metacarpal bone perfectly.
The shaft/ body of the large metacarpal bone shows the following osteological features –
- A cylindrical shaft of the metacarpal,
- Dorsal and palmar surfaces,
- Dorsal longitudinal/vertical vascular shallow groove,
- Palmar longitudinal/vertical shallow groove,
- Proximal and distal foramina on the dorsal vascular groove,
- Proximal and distal foramina on the palmar vascular groove, and
- Lateral and medial borders of the shaft,
Again, the proximal extremity of the large metacarpal shows the following osteological features –
- Large medial articular facet,
- Small lateral articular facet, and
- Metacarpal tuberosity (on the dorso-medial aspect),
The distal extremity of the cow’s large metacarpal bone shows the following osteological features –
- Lateral and medial condyles,
- The intercondyloid cleft between the two condyles, and
- Four depressions on the palmar aspect (for the proximal sesamoid bones),
All the above-mentioned osteological features from the cow’s large metacarpal are shown in Figure 5.
Now, I will describe these osteological features from the shaft and extremities of the cow’s large metacarpal bone.
The shaft of the cow’s large metacarpal bone
The shaft of the large metacarpal bone of a cow is irregular and semi-cylindrical. It possesses two surfaces: dorsal (anterior) and palmar (posterior), and two borders: lateral and medial.
Dorsal surface of the shaft
Here, the dorsal surface is convex transversely and traversed vertically by a shallow groove. This groove is placed in the centre of this surface and known as the dorsal longitudinal/vertical vascular groove.
This vertical vascular groove on this surface is for the passes of vessels. You will find two foramina on this vascular groove: one is proximal, and the other is distal.
These foramina traverse the thickness of the shaft of the metacarpal bone. Finally, they communicate with the corresponding proximal and distal palmar foramina.
Here, Figure 6 shows the features of the dorsal surface of the shaft of a cow’s large metacarpal bone.
Palmar surface of the shaft of the metacarpal bone
The palmar surface of the shaft of the cow’s metacarpal bone is almost flat and broad at both extremities. This palmar surface also presents a shallow vertical groove, similar to the dorsal vertical groove.
The vertical groove on the plamar surface also presents two foramina: proximal and distal. But, they are smaller than those of the dorsal foramina.
Except in the cow, the palmar surface is the contact surface (in dog/ cat) that faces toward the ground. This surface also supports the suspensory ligaments / superior sesamoid ligaments.
Here, Figure 7 shows the osteological features of the palmar surface of the shaft of the cow’s large metacarpal bone.
Why does the groove occur in the surfaces of the shaft of the metacarpal?
Well, the grooves occur on both surfaces of the cow’s metacarpal shaft due to the fusion of the third and fourth metacarpals. The dorsal groove is deep and distinct compared to the palmar groove on the metacarpal bone.
Borders of the cow’s metacarpal shaft
The borders of the metacarpal’s shaft in a cow are lateral and medial. Both the lateral and medial borders are rounded and smooth.
The small metacarpal bone V attaches to the proximal third of the lateral border of the large metacarpal’s shaft. Here, Figure 8 shows the borders of the metacarpal shaft of a cow. It also shows the attachment of the small metacarpal bone to the lateral borders of the metacarpal’s shaft in the cow.
Proximal extremity of the cow’s large metacarpal
The proximal extremity of the large metacarpal of a cow possesses two concave facets. These facets are separated by a median ridge and are termed the medial and lateral facets.
The medial facet on the proximal extremity of the cow’s metacarpal is larger and articulates with the fused second and third carpal bones.
Lateral facet on the proximal extremity of the cow’s metacarpal: smaller and articulates with the fourth carpal bone.
You will also find a small convex facet just below the articular surface on the lateral aspect. This facet articulates with the small metacarpal bone.
Again, the proximal extremity of the cow’s metacarpal presents a metacarpal tuberosity at the dorso-medial aspect. The tendon of the cow’s extensor carpi radialis muscle attaches to this metacarpal tuberosity.
You will also find a rough elevation on the dorsal proximal extremity of the metacarpal. This elevation is for the attachment of the ligament of the ulnaris lateralis muscle of the forearm.
Here, Figure 9 shows the lateral and medial facets, metacarpal tuberosity from the proximal extremity of the cow’s large metacarpal bone.
Distal extremity of the large metacarpal bone in a cow
The distal extremity of the cow’s large metacarpal bone presents lateral and medial condyles. A sagittal cleft separates these lateral and medial condyles. This sagittal cleft is also known as the intercondyloid cleft in the metacarpal bone.
Both condyles represent the distal extremity of one metacarpal and are important for identifying the right/left bone.
You will see a sagittal ridge that divides each condyle into two articular surfaces. These two articular surfaces are for articulation with the proximal extremity of the first phalanx.
The palmar aspect of the distal extremity of a cow’s metacarpal presents four depressions. These depressions are the unique osteological features of metacarpals and host four sesamoid bones.
These sesamoid bones, along with the first phalanges, form the lateral and medial fetlock joint in the forelimb.
Here, Figure 10 shows the osteological features from the distal extremity of the cow’s metacarpal bone.
Cow’s small metacarpal
The small metacarpal in a cow is a small, elongated piece of bone in the metacarpus. It is considered a modified long bone in the cow’s skeleton.
The small metacarpal V is situated at the proximal part of the lateral border of the large metacarpal V. As this cow’s small metacarpal V is also a long bone, it possesses the followings –
- Shaft: the small metacarpal has a shaft that attaches to the proximal part of the large metacarpal bone.
- Proximal extremity: it is rounded and bears a small facet on its dorsal (anterior) surface. Actually, this facet is for articulation with the large metacarpal V bone.
- Distal extremity: it is pointed and don’t possesses any remarkable osteological features.
Here, Figure 11 shows the cow’s small metacarpal bone along with their location in the manus, attachment to the large metacarpal bone.
Comparison of metacarpals in cow, horse, and dog
You may easily compare the metacarpals in the cow, horse, and dog with their key identifying features. Here, the horse metacarpals are also of two types, like the cow: large and small.
But the number is variable in horses, one large metacarpal and two small metacarpals. Here, the large metacarpal is III, and metacarpals II and IV are the small metacarpals in the horse. These small metacarpals in horses are known as splint bones.
Here, the horse’s metacarpals are more cylindrical and massive than the cow’s metacarpals. The metacarpal tuberosity is larger than that of the horse. Again, the distal extremity resembles one condyle of the distal extremity of cow’s metacarpal.
The dog possesses five metacarpals, where the first one is the shortest, the third and fourth are larger. Here, the shafts of the dog’s metacarpals are compressed in the dorso-palmar aspect.
Table 1 presents the key comparison of the metacarpals of the cow, horse, and dog –
| Features | Cow metacarpals | Horse metacarpals | Dog metacarpals |
| Large metacarpals | 2 (III and IV) | 1 (III) | 5 (I, II, III, IV, V) |
| Small metacarpals | 1 (V) | 2 (II and IV) | |
| Shaft of metacarpals | Semi-cylindrical | Cylindrical | Compressed |
| Vertical grooves | PresentDorsal and ventral | Absent | Absent |
| Condyles | Two Lateral and medial | Single | Single in each metacarpal |
| Depression for sesamoids | Four | Two | Two (except for first metacarpal) |
Here, Figure 12 shows the comparison of the metacarpals of the cow, horse, and dog.
How to identify the right and left metacarpal bones in a cow?
To identify the right and left metacarpal bones from the cow’s forelimb, you should consider the followings landmarks –
- Surfaces of the shaft: the dorsal surface is convex, and the palmar surface is almost flat.
- Grooves on dorsal surfaces: the dorsal vertical groove is deep compared to palamr vertical groove.
- Formina on grooves: proximal and distal foramina are distinct and large in the dorsal vertical groove.
- Facets on the proximal extremity: the medial facet is larger, whereas the lateral facet is smaller.
- Features in the distal extremity: present lateral and medial condyles, and the palmar surface presents four depressions for the sesamoid bones.
First, you should identify the proximal and distal extremities of the cow’s metacarpal bones.
Second, you should identify the medial and lateral borders with the help of the larger medial articular surface from the proximal extremity of the metacarpal.
Third, as you already identified proximal, distal, lateral, and medial, now you should hold this bone with your right/left hand on vertical direction.
Fourth, make sure the dorsal surface is convex, the larger articular surface faces medially, and the condyles face distally.
Here, Figure 13 shows the identifying process of the right and left metacarpal bones from the cow’s forelimb.
Why is this cow’s right metacarpal bone?
Figure 14 shows the cow’s right metacarpal bone.
Let’s explain why this is the cow’s right metacarpal bone. Well, it is the cow’s right metacarpal for the following causes –
- First, the larger facet on the proximal extremity faces the medial aspect.
- Second, the condyles faces distal extremity.
- Third, the dorsal surface is convex.
- Fourth, the extremity shows four depressions for sesamoids that faces palmar aspect.
Now, hold the metacarpal bone with your right hand in a vertical direction; you will find the features that matched with above-mentioned features. Thus, this is the right side metacarpal bone from the cow’s forelimb.
Conclusion
So, the cow metacarpal consists of two fused single large metacarpal bones and a single small metacarpal bone. Here, the third and fourth metacarpal bones fused to form a single large metacarpal in the cow’s forelimb.
The cow’s large metacarpal possesses the shaft and extremities like a typical long bone. Here, the dorsal and palmar vertical vascular groove is one of the key identifying features of the cow’s large metacarpal bone.
Again, larger medial facets on the proximal extremity, and palmar distal depressions for sesamoids are also identifying features of the cow’s metacarpal. The small metacarpal is a modified long bone in cows that possesses a shaft, proximal, and pointed distal extremity.
References
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- Mcleod, W. N.: Bovine anatomy, 2nd Edn. Burgess publishing co. Minneapolis.
- Dyce, K. M., W. O. Sack and CSG Wensing : Text Book of Veterinary Anatomy, Lea & Febiger. Philadelphia
- Yousif, Anatomical study of the 3rd metacarpal bone of some mammals. GSC Biol and Pharm Sci, 2023, 23(02), 197–201.
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