Animal vertebrae identification

Animal vertebrae identification is the key requirement for students to learn deeply about them. Here, I will discuss the animal vertebrae identification from different animals with diagrams.

Quick answer: animal vertebrae identification is to identify the cervical, thoracic, lumbar, sacral, and caudal bones of the vertebral column according to their unique osteological features.

Thus, this guide will help you to identify all the bones from the animal’s vertebral column perfectly.

Animal vertebrae identification

Animal vertebrae are the median unpaired irregular type of bones of the axial skeleton. Based on the shape and position, these animal vertebrae are classified as five regions –

• Cervical vertebrae: have well-developed articular processes (except first and second vertebrae).
• Thoracic vertebrae: possess well-developed spinous processes and articular facets for the ribs.
• Lumbar vertebrae: they have a large, flat transverse process that projects from the lateral to the pedicle.
• Sacral vertebrae: they fused to form the single sacrum in animals.
• Coccygeal/ caudal vertebrae: they form the basis of the tail, and most of them are rod shape structure without processes (except the first three).

Again, the number and shape of these 5 types of vertebrae are also variable in different species. Thus, the vertebral formula of domestic animals also varies.

Here, Figure 1 presents the five types of animal vertebrae identification with their unique osteological feature.

But, to understand the features of these vertebrae perfectly, you might know an animal’s typical vertebra. Make sure you also know the osteological terms that are used in describing the animal vertebrae perfectly.

According to an animal’s typical vertebra, it possesses the followings –

• Body: it is cylindrical and has convex cranial and concave caudal extremities.
• Arches: present on both sides of the neural ring and consist of a ventrolateral pedicle and dorsal plate or laminae.
• Processes: they are single spinous, right and left transverse, and paired cranial and caudal articular processes.

Here, Figure 2 shows the body, arches (pedicle and laminae), three types of processes, and the neural ring of animal’s typical vertebra.

Now, these features might help you to identify the animal’s cervical, thoracic, lumbar, sacral, and caudal vertebrae perfectly.

Cervical vertebrae in animals

The cervical vertebrae contribute to forming the skeleton of the animal’s neck anatomy. Except few animals, there are seven in number in the vertebral column.

Here, the first and second cervical vertebrae of animals are highly modified and deviate greatly from normal structure. The next three (third, fourth, and fifth) cervical vertebrae of animals are almost similar. They confirm the general architectural plan of an animal’s typical vertebra.

Again, the animal’s six and seventh cervical vertebrae have some special features. But they do not deviate much from the general architectural plan of a vertebra.

Here, I will present the identification points for each cervical vertebra from different animals, such as the cow, goat, horse, and dog. I will also point out the key differentiating features of cervical vertebrae in different animal species.

Here, Figure 3 shows the seven cervical vertebrae from the necks of different animals.

First cervical in animals identification (atlas)

The first cervical vertebra of an animal is also called the atlas, as it supports the globe of the head. It is an atypical vertebra in animals that lack body and spinous processes.

The following osteological features might help you to identify the first cervical vertebra of animals –

• It possesses the dorsal and ventral arches that form the bony ring.
• The thin dorsal arch present dorsal median tubercle, whereas the thick, narrow, less curved ventral arch also presents a ventral medial tubercle.
• The caudal border of the ventral arch presents a transverse concave articular area (known as fovea dentis).
• A deep articular cavity is present on the cranial edge of the neural ring for articulation with the occipital condyle of the skull.
• From the bony neural ring, two extensive curved plates projecting ventrolateral and caudally (known as wings).
• The dorsal convex surface of the wings presents two foramina in the depression on the cranial aspect (alar and intravertebral).
• Again, a transverse foramen is found in some species (horse, dog) at the caudal aspect of the dorsal surface of the wing.
• The ventral surface of each wings present a concave depression (known as the atlantal fossa)

Thus, this is the first cervical vertebra of an animal. Here, Figure 4 shows the typical identifying features of the animal’s first cervical vertebra.

Comparative features of the first cervical/atlas bone in different animals

The basic structure of the first cervical vertebra (atlas bone) is almost similar in different animal species, with a few exceptions. Let’s see the comparative osteological features of the first cervical vertebra from ruminant, horse, and dog in Table 1 –

Features	Ox’s atlas bone	Horse’s atlas bone	Dog’s atlas bone
Wings	Curved ventrolaterally and caudally	Curved ventrally and laterallyThinner than ox	Flattened and horizontal
Transverse foramen	Absent	Present	Present
Intervertebral foramen	Present	Present	Present
Alar foramen	Present	Present	Alar notch present on cranial aspect of wing
Dorsal tubercle	Present and thick	Present and more thick	Absent

Thus, these are the key differentiating osteological features of the first cervical vertebra in different species. Again, Figure 5 also shows the differentiating osteological features of an animal’s first cervical vertebra.

Animal second cervical vertebra identification

The animal’s second cervical vertebra is also atypical and called the axis. This is because its dentate process acts like the axis where the atlas moves in half rotation.

This second cervical is also known as the dentate vertebra. This is because of its tooth like appearance of the process projecting from the cranial extremity.

Followings are the identifying osteological features of the second cervical vertebra from animals –

• It possesses a longest body that has a cranial odontoid process for articulation with the fovea dentis.
• The dorsal surface of the odontoid process is concave, while the ventral surface is convex.
• The cranial extremity of the body also possesses a nearly flat articular surface that continues with the ventral surface of the odontoid process.
• Like the typical vertebra, the caudal extremity of its body is strongly concave to receive the cranial extremity of the third vertebra.
• The caudal edge of the pedicle presents notches on either side, whereas cranial notches are ill-developed.
• Again, the pedicle presents special oval intravertebral foramina just behind the cranial notches.
• It presents a large and strong spinous process, which is narrow cranially and thick and wide caudally (varies in species).
• The cranial articular process is absent, whereas the caudal articular process is directed backward.
• It present small, undivided, and caudally directed transverse process with a small transverse foramen.

Thus, this is the second cervical vertebra of the animal. Here, Figure 6 shows the key identifying osteological features of the animal’s second cervical vertebra.

Comparative anatomy of the second cervical vertebra in different animals

Table 2 shows the differentiating features of the second cervical vertebra (axis bone) among different animals, such as ruminants (cow/ox), horses, and dogs.

Features	Ox’s axis bone	Horse’s axis bone	Dog’s axis bone
Body	Longest	Larger than ox	Longer
Odontoid process	Wide and rounded	Longer, narrower, and conical	Rounded and longer
Spinous process	Large and strong	Massive Divided into two ridges (caudally)	LargerOverhangs the ring of atlas
Transverse process	Small	Narrow	Narrow
Intravertebral foramina	Present	Present	Cranial notch developed

So, the appearance of the odontoid process, spinous process, and intravertebral foramen after the cranial notch on the pedicle can differentiate the axis among species. Here, Figure 7 shows the second cervical vertebrae of ruminant, horse, and dog with their unique features.

Third, fourth, and fifth cervical vertebrae in an animal

Identification of the third, fourth, and fifth cervical vertebrae in animal are so easy as they possess common features of typical vertebrae. However, followings are the common features of these vertebrae in animals that differ from other vertebrae –

• They possess a long body with convex cranial and concave caudal extremities.
• They also present a ventral spine in the ventral part of their body.
• These vertebrae present very strong arches and deep notches on both pedicles.
• The facets on the cranial and caudal articular processes are larger.
• The spinous processes of these vertebrae are short and thick (vary in species).
• Each transverse processes of these three vertebrae are divided into dorsal and ventral segments.
• The transverse processes of these vertebrae present a transverse foramen.

Thus, these are the third, fourth, and fifth cervical vertebrae of animals. Here, Figure 8 shows the animal’s third, fourth, and fifth cervical vertebrae with their typical osteological features.

Sixth vs seventh cervical vertebrae in animals

The sixth cervical vertebra of an animal is resemble to preceding vertebra with the following exceptions –

• It presents a wide but shorter body.
• The dorsal spinous process and articular processes of the sixth cervical are well-developed.
• The ventral part of the transverse process is well-developed and is in the form of a quadrilateral plate.
• The quadrilateral plate extends considerably below and behind the level of the body.
• It does not possess the ventral spine.

Here, Figure 9 shows the exceptional features of the animal’s sixth cervical vertebra.

However, the seventh cervical vertebra of the animal has the following special osteological features –

• The body of the seventh cervical vertebra of an animal is the shortest of all the cervical vertebrae.
• It possesses a flattened, dorsally directed, well-developed spinous process (has little species difference).
• The transverse process is single and undivided.
• It lacks a transverse foramen.
• The caudal end of the body bears one pair of semicircular facets for articulation with the head of the first pair rib.

Here, Figure 10 shows the special osteological features of the animal’s seventh cervical vertebra.

Now, you may easily compare the osteological features between the sixth and seventh cervical vertebrae. Table 3 shows the key differentiating features of the sixth cervical from the seventh cervical vertebra of animals –

Fetaures	Animal sixth cervical	Animal seventh cervical
Body	Wide but shorter	Shortest
Transverse process	Divided into dorsal and ventral parts	Single and undivided
Quadrilateral plate	Present	Absent
Transverse foramen	Present	Absent
Spinous process	Longer	Flat and well-developed
Facets on body	Absent	Present one pair facets on caudal end

Species variation of the sixth cervical vertebra

You will find a few species variations of the sixth cervical vertebra. Here, Table 4 shows the key variations of the sixth cervical vertebra among ruminant, horse, and dog –

Features	Ruminant’s sixth cervical	Horse’s sixth cervical	Dog’s six cervical
Transverse process	Two parts	Three parts	Two parts
Spinous process	Longer	Rudimentary	Smaller

Here, Figure 11 also shows the unique features of the sixth cervical vertebra in different animal species.

Animal thoracic vertebrae identification

The thoracic vertebrae form the skeleton of an animal’s thoracic cage along with ribs, sternum, and costal cartilages. With a few exceptions, most of the domestic animals possess thirteen thoracic vertebrae in their vertebral column.

Two characteristic features of animal thoracic vertebrae make them unique from other vertebrae –

• Body of these vertebrae possess paired cranial and caudal capitular facets for articulation with the head of the rib (except first and last).
• Presence of a long dorsal spinous process for attachment of the back muscle and the supraspinous ligament.

Here, Figure 12 shows the unique osteological features of animal thoracic vertebrae.

How to identify an animal’s thoracic vertebrae?

For animal thoracic vertebrae identification, you may follow the following features –

• The bodies of the animal thoracic vertebrae are shorter than those of the other regions of the vertebral column.
• The cranial and caudal articular ends of the body present a pair of capitular facets on both sides.
• Their bodies also present a distinct constriction at the middle and a ventral crest.
• An additional intravertebral foramen is present on both sides of the arches.
• The spinous processes of animal thoracic vertebrae are longer and directed backward (direction varies in species).
• They present thick, short, undivided, and strong transverse processes with tuberous free ends.
• On the ventrolateral aspect, the transverse process has a tubercular facet for articulation with the tubercle of a specific rib.
• The cranial articular processes are ill-developed and are in the form of small oval facets on the dorsal aspect of the lamina.
• Again, the caudal articular processes are located at the caudo-ventral aspect of the longer spinous process.

Thus, these are the typical features of the animal thoracic vertebrae.  

Exceptions: the last thoracic vertebra only possesses one pair of cranial capitular facets on the body. They are designed for articulation with the head of the last pair of ribs. Again, the last thoracic vertebra has the short, straight vertical spine/spinous process.

Comparative anatomy of thoracic vertebrae in animals

The ruminant, horse, and dog show little variation in their thoracic vertebrae. Table 5 shows the comparative anatomy of thoracic vertebrae in different animals –

Features	Ox’s thoracic vertebrae	Horse’s thoracic vertebrae	Dog thoracic vertebrae
Number	Thirteen	Eighteen	Thirteen
Body	Shortest	Shorter	Wider
Notch on pedicles	Shallow	Deep	Shallow
Spinous process	Directed backward	Directed backward	Variable Directed straight and forward
Accessory process	Present	Absent	Present

So, you can differentiate the ruminant, horse, and dog’s thoracic vertebrae from their body and spinous processes. Here, Figure 13 shows the thoracic vertebrae of different animal species.

Animal lumbar vertebrae identification

The lumbar vertebrae form the skeleton of an animal’s abdomen. Again, the lateral and ventral wall of the animal’s abdomen is formed by the abdominal muscles.

Most domestic animals possess six lumbar vertebrae in their vertebral column. Followings are two unique features of the animal lumbar vertebrae that make them different from other vertebrae –

• They possess a dorsoventrally compressed larger body.
• They are also characterized by the great size and form of their transverse processes.

Here, Figure 14 shows the typical osteological features of animal lumbar vertebrae.

How to identify the animal’s lumbar vertebrae?

Well, followings are the key osteological features that help you to identify the animal’s lumbar vertebrae –

• The wide compressed body of the lumbar vertebrae consists of moderate convex cranial and concave caudal extremities.
• A gradual increase in height and wide occurs in the arches of the animal lumbar vertebrae.
• The caudal notches on the arches are deeper than the cranial notches.
• Again, the first few lumbar vertebrae of an animal present double intervertebral foramina.
• The cranial articular processes are concave and directed inward.
• They also possess caudal articular processes, which are convex and directed inward.
• These lumbar vertebrae possess the elongated and dorsoventrally flattened transverse process (varies in species).
• The spinous processes of these vertebrae are broad, flattened plates, and are of the same height.
• However, the first few vertebrae present the rounded neural ring and gradually become triangular at the last lumbar.
• The intervertebral foramina are larger between the animal’s lumbar vertebrae.

Thus, these are the animal’s lumbar vertebrae. You will find serial changes in the body, arches, and processes of the animal’s lumbar vertebrae.

The transverse processes of the animal’s lumbar vertebrae are slightly curved downward. It is shorter in the first lumbar vertebra and gradually increases up to the fifth lumbar.

The spinous processes of the animal’s last lumbar vertebra is narrowest of all the six lumbar vertebrae. You will find a ventral rudimentary spinous process in the animal’s lumbar vertebrae.

Species variation of lumbar vertebrae

A great species variation of the lumbar vertebrae occurs in the domestic animals. Table 6 shows the key osteological variations of the lumbar vertebrae in different species, such as ruminant, horse, and dog.

Features	Ox lumbar vertebrae	Horse lumbar vertebrae	Dog lumbar vertebrae
Number	Six	Six	Seven
Body	Wide, compressed	Shorter	Wider, compressed
Ventral spine	Present	In first three
Transverse process	Slightly curved downward	Direction: varies First two: curved caudalLast two: curved cranial	Plate like Direction: craniad and ventrad
Facets on process	Absent	Present on caudal border of transverse process of the last lumbar	Absent

Exceptions in horse lumbar: the caudal border of the transverse process of the horse’s fifth lumbar possesses a concave facet on its base. It is for the articulation with the cranial convex facet on the cranial border of the sixth lumbar.

Again, the caudal border of the transverse processes of the horse’s sixth lumbar presents a large concave facet. They articulate with the cranial convex facets of the horse’s sacrum bone.

Exceptions in dog lumbar: the bodies of the dog lumbar vertebrae increase gradually in wide. Their transverse processes are plate-like and directed cranially and dorsally.

The length of their transverse process increases from first to fifth. Except for the last, the extremities of the transverse processes are expanded.

Here, Figure 15 shows the exceptional features of the lumbar vertebrae from different domestic animals.

Animal sacrum bone identification

The sacral vertebrae fused to form the single sacrum bone in animals. Here, the number of the sacral vertebrae is variable in different domestic animals.

The sacrum forms the roof of the animal’s pelvic cavity. It is roughly triangular in form and wedged between the right and left iliac bones of the pelvis.

The animal sacrum possesses –

• Two surfaces: dorsal and ventral.
• Two borders: right lateral and left lateral.
• A base: cranial extremity of the animal sacrum.
• An apex: caudal extremity of the sacrum.

Dorsal surface of the animal sacrum

The dorsal surface of the animal sacrum bone presents a median sacral crest. It extends craniocaudally from the base to the apex of the sacrum.

The fusion of the supraspinous processes of the sacral vertebrae forms this median sacral crest. This feature is very common in ruminants, and variations occur in other species.

On either side of the median sacral crest, another crests running parallel to this crest. They are known as the right and left lateral sacral crests of the sacrum.

The fusion of the articular processes of the sacral vertebrae forms these lateral sacral crests. Here, Figure 16 shows the shape, dorsal surface, median sacral crest, and lateral crest of the ruminant sacrum bone.

The dorsal surface of the animal sacrum bone also shows the four pairs of dorsal sacral foramina. Again, the cranial two foramina are located at the medial aspect, and the caudal two are located at the lateral side of the lateral sacral crest.

Ventral surface of the animal sacrum

The ventral surface of the animal’s sacrum is smooth and concave. It forms the roof of the pelvic cavity and presents a ventral median longitudinal groove.

This surface also presents four transverse lines that indicate the fusion of the five sacral vertebrae. However, the number of lines varies in different animal species.

On either end of these transverse lines, there are four pairs of ventral sacral foramina. Again, the number of the dorsal and ventral sacral formina varies on animals.

Here, Figure 17 shows the features from the ventral surface of the animal sacrum. It shows the median longitudinal groove, transverse lines, and ventral sacral foramina.

Here, the right and left lateral borders of the animal sacrum bone are concave and thin. They provide attachment to the sacro-sciatic ligament with the pelvic bones.

Base of the animal sacrum

The cranial extremity of the first sacral vertebra forms the base of the animal sacrum. Its cranial surface is convex and articulates with the concave caudal extremity of the last lumbar.

The neural ring of the sacral vertebrae is triangular. Here, the cranial articular process of the sacrum bone is large and widely separated.

The transverse processes of the animal sacral vertebrae fused to form a broad wing cranially and a lateral plate caudally. Here, the wing is twisted and articulates with the corresponding articular surface of the ilium bone.

Figure 18 shows the osteological features of the base of the animal sacrum bone.

Apex of the animal sacrum

The caudal extremity of the last sacral vertebra forms the apex of the animal sacrum. It presents a small triangular neural ring caudally.

The median sacral crest caudally projects above the neural ring. You will find a caudally directed projection on either end of the body of the last segment of the animal sacrum. It is actually the transverse process of the last sacral vertebra of the animal sacrum bone.

How to identify the animal sacrum bone practically?

Well, this is very easy to identify the animal sacrum bone by following the identifying points –

• The animal sacrum presents a triangular shape structure that is formed by the fusion of sacral vertebrae.
• It presents a dorsal longitudinal median sacral crest along with two parallel lateral sacral crests.
• The ventral surface is concave and smooth, that present median longitudinal groove and transverse lines (varies in animals).
• Both the dorsal and ventral surfaces present four/less formina (varies in animals).
• The base is wide and presents a triangular neural ring, broad wings, and larger cranial articular facets.
• Again, the apex also present small triangular neural ring and a caudally directed transverse process.

Thus, this is the sacram of an animal.

Comparative anatomy of the sacrum in domestic animals

The sacrum bone in domestic animals varies greatly.  You may easily compare the sacrum of ruminants with that of the horse and the dog, with their unique features.

Here, Table 7 shows the comparative anatomy of the sacrum bone in different domestic animals –

Features	Ox sacrum bone	Horse sacrum bone	Dog sacrum bone
Sacral vertebrae	Five	Five	Three
Spinous process	Complete fusion	Incomplete fusion	Complete fusion
Median sacral crest	Present	Absent	Present, notched
Lateral sacral crest	Developed	Ill-developed	Developed
Ventral surface	Concave	Less concave	Concave
Wing of sacrum	Broad	Pointed, prismatic	High, prismatic
Facets on sacrum	Absent	Oval cranial facets	Absent
Sacral foramina	Four pairs	Four pairs	Two pairs

So, the variations are found in the wing, median sacral crest, facets on the sacrum, and sacral foramina of different animals’ sacra. Here, the horse sacrum presents a pointed and prismatic wing.

On its cranial aspect, you will find oval convex articular facets on both sides. They articulate with the corresponding caudal concave facets of the transverse process of the last lumbar vertebra.

Again, it lacks a median sacral crest as there is incomplete fusion of the spinous processes of the sacral vertebrae.

However, the dog’s sacrum is relatively smaller and formed by the fusion of its three sacral vertebrae. It presents a notched median sacral crest. Here, Figure 19 shows the comparative anatomy of the sacrum bone from different domestic animals.

Animal coccygeal vertebrae identification

The coccygeal/caudal vertebrae mainly form the skeleton of the animal’s tail. It also have the partial contribution to complete the roof of the animal’s pelvic cavity.

These vertebrae vary considerably in number in different animals. From first to last, they become reduced in size. Except for the first two or three coccygeal vertebrae, most of them have only the bodies.

For animal coccygeal vertebrae identification, you might have the following basic knowledge on them –

• The first coccygeal vertebra of an animal may be fused with the last sacral vertebra of the sacrum.
• You will find a body and a few modified processes in the first three coccygeal vertebrae of animals.
• Bodies of the animal’s coccygeal vertebrae are dorsoventrally flattened and constricted at the middle.
• A median groove is present on the ventral surface of the animal’s coccygeal vertebrae.
• The arches of these three coccygeal vertebrae are small and triangular, where the cranial notches are absent.
• A thicken short spinous process is present in the first three coccygeal vertebrae.
• The transverse processes of these vertebrae are relatively large plates that project horizontally outward.

Here, Figure 20 shows the typical features of the coccygeal vertebrae of animals.

Exceptions in horse coccygeal vertebrae: There are eighteen to twenty coccygeal vertebrae in the horse vertebral column. The lamina of the coccygeal vertebrae beyond the fourth vertebrae fail to meet dorsally.

Exceptions in dog coccygeal vertebrae: the first five or six coccygeal vertebrae of a dog are developed with bodies, arches, and processes. You will also find the neural rings in the first five or six coccygeal vertebrae of the dog.

FAQ’s on animal vertebrae

Conclusion

Thus, animal vertebrae identification is easy if you have the basic osteological features of different segments of the vertebral column. Except for the atlas and axis, other cervical vertebrae of animals almost present the features of a typical vertebra.

Again, animal thoracic vertebrae are featured by a well-developed spinous process and articular facets for ribs. However, the animal lumbar vertebrae have large, flat transverse processes that projects lateral.

Finally, the animal sacral vertebrae fused to form a single wedge-shape sacrum bone. Again, variable numbers of coccygeal vertebrae form the bony basis of the animal’s tail.

References

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