Cow atlas bone

The cow atlas bone is the first cervical vertebra of the skeleton of the neck. Here, I will describe all the osteological features of the cow’s atlas with schematic diagrams and real pictures.

Quick answer: Cow atlas bone is an atypical vertebra that only possesses a bony ring and curved plates, but lacks a body and a spinous process.

The information that is provided in the cow atlas description is also exam-focused. Thus, you will learn the identification of the cow atlas and prepare yourself for the theory examination.

Cow atlas bone

Figure 1 shows the schematic diagram/presentation of a cow atlas and a typical vertebra. Here, the cow atlas is deviated greatly from the general structure plan of the typical vertebrae of the vertebral column.

So, first, let’s know what the deviations of the atlas from the typical vertebra are. Does it show modification in the body, arches, and three different processes?

Well, the figure shows that the body and spinous process of the cow’s atlas are absent. Again, the dorsal and ventral arches form the bony ring of the atlas.

However, two large curved plates project laterally from the right and left sides of the bony ring. The curved plates of the cow’s atlas are also known as the wings.

The bony ring of the atlas encloses the vertebral foramen. It forms part of the vertebral canal through which the spinal cord passes.

Now, let’s identify the different features of the cow’s atlas. That might help you to understand what you should describe from it.

Here, Figure 2 shows arches, curved plates, and bony rings of a cow atlas with their different features.

Thus, you need to describe the following from the cow’s atlas –

• Arches: features of the dorsal and ventral arches.
• Curved plates/wings: it consists of right and left lateral wings with different foramina and fossa.
• Bony ring: it consists of different features in its cranial and caudal edges/extremities.

Arches of the cow atlas

Compared to the cow’s typical vertebra, the atlas shows a great modification in its arch structure. Here, the lamina and pedicle are not applicable for cow atlas.

Figure 3 shows the extension of the dorsal and ventral arches from the cow’s atlas.

• Dorsal arch of atlas: It is dome-shaped, more curved, and forms the dorsal wall of the bony ring. It presents an exterior median dorsal tubercle.
• Ventral arch of atlas: It is thicker, narrower, and less curved than the dorsal arch. It also possesses a median ventral tubercle externally.  

Here, the median ventral tubercle of the cow’s atlas provides attachment to the longus colli muscle of the neck. However, the inner surface of the ventral arch presents a transverse articular area near its caudal border. It is the fovea dentis where the dens/odontoid process of the cow’s axis vertebra rests.

Again, cranial to the fovea dentis, there are some rough areas for attachment of the dentis ligament. However, the dorsal and ventral arches possess two lateral masses externally.

Sometimes, the thick ventral arch is considered the body of the cow’s atlas according to some anatomists (Ghosh, 2000).

Wings of the cow atlas bone

Figure 4 shows the right and left lateral wings of the cow’s atlas that project from the bony ring.

These are the extensive curved plates of the cow’s atlas. They are projecting ventrolaterally and caudally from the respective lateral masses of the atlas.

However, both wings present two descriptive surfaces: dorsal and ventral, with unique features.

Dorsal surface of the wing

Here, the dorsal surface of the wings is convex except in the middle. Figure 5 shows the dorsal convex surface of the wing of a cow atlas.

The figure presents one depression on the cranial aspect of the dorsal surface of both wings. Within this depression, you will find two foramina –

• Intravertebral foramen: It is medial in position and has a connection with the neural/vertebral ring of the cow atlas bone.
• Alar foramen: It is lateral in position within the depression and has a connection with the ventral surface of the respective wings.

Here, the intravertebral foramen gives passage to the first spinal nerve of the cow. The branch of the vertebral artery also passage within this intravertebral foramen of the cow’s atlas bone.

However, the alar foramen of the cow’s atlas gives passage to the dorsal branch of the first spinal nerve.

Just caudal to the depression, there are two foramina in the linear groove on the dorsal surface.

Ventral surface of the wings

The ventral surface of both wings is concave and termed the fossa atlantis/atlantal fossa. This is a cavity actually located between the ventral surface of the wings and the lateral masses of the atlas vertebra.

You will also find similar foramina (intravertebral and alar) from the ventral concave surface of wings. Here, Figure 6 shows the atlantal fossa (deep cavity/depression) from the ventral surface of both wings of the cow’s atlas.

Extremities of the bony ring of the cow atlas

Figure 7 shows the edges/extremities of the bony ring of the cow’s atlas bone.

Thus, there are two edges/extremities in the bony ring of the atlas vertebra –

• Cranial edge/extremity, and
• Caudal edge/extremity.

Here, the cranial extremity of the bony ring of a cow’s atlas presents notches on both dorsal and ventral aspects. You will find a deep articular cavity on each side of the cranial extremity of the bony ring.

These two deep articular cavities are shown in Figure 8 and termed the condyloid fossa. They are designed for articulation with the corresponding occipital condyles of the cow’s skull.

The caudal extremity of the bony ring is sharp and rough on its upper parts. It presents one central and two lateral notches.

However, the lower part of the caudal extremity presents an extensive, nearly flat, smooth articular surface. It is the fovea dentis which articulates with the axis.

Here, Figure 9 shows the features from the caudal extremity of the cow’s atlas bony ring. All the notches from the upper part and the smooth articular surface from the lower part of the ring are identified in the figure.

Actually, the lower articular surface or fovea dentis is divided into right and left areas. They continue with each other across the ventral midline of the cow atlas vertebra.

FAQ’s on the cow’s atlas bone

Conclusion

So, the cow atlas bone is an atypical vertebra that deviates greatly from the typical vertebra. It consists of a large bony ring formed by the dorsal and ventral arches and two curved wings.

Here, the dorsal surface of the curved wings presents a depression which contains two foramina. Again, the ventral surface of the wings of the cow’s atlas present atlantal fossa.

The most unique features from the cranial aspect of the bony ring are the presence of two condyloid fossae. Whereas, the presence of the fovea dentis for the odontoid process of the cow axis is a unique feature from the caudal aspect of the bony ring.

References

• Ghosh, R. K.: Primary veterinary anatomy, 2nd Edn.Current Books International, Kolkata.
• Sathapathy S et al., Gross morphological and biometrical Studies on the typical cervical vertebrae of Blue bull (Boselaphus tragocamelus). Indian Journal of Animal Research. 2018; 53(6): 741-745. 
• Rowen D. Frandson, W. Lee Wilke, and A. Dee: Anatomy and physiology of farm animals, 4th edn.Wiley-Blackwell, USA.
• Smuts, The Foramina of the Cervical Vertebrae of the Ox. Anatomia, Histologia, Embryologia, 1974; 3: 296-307.  
• Getty, R. S. & G.’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.