Animal body cavities

Knowledge of animal body cavities is required to study the visceral organs of the digestive, respiratory, and urinary systems. However, it is also essential for describing the course of vessels, nerves, and other structures that pass between cavities.

Here, I will describe the various cavities in the animal’s body with hand-drawn diagrams and real pictures.  

Quick answer: Animal body cavities are cranial, thoracic, abdominal, and pelvic, which protect and accommodate specific organs within specific limits.

Thus, I will first identify these 4 main cavities, then describe their boundaries and contents.

What are the different types of body cavities in animals?

Figure 1 presents a hand-drawn presentation on the different body cavities in animals. Here, I have only highlighted the major cavities from the animal’s body.

Thus, according to the figure, the following are the major body cavities in animals –

• Cranial cavity: It is the major cavity of the head region of an animal (Cow, horse, sheep, goat, and dog).
• Thoracic cavity: This is the first visceral cavity, which is also known as the chest cavity. However, it accommodates various vital organs.
• Abdominal cavity of animals: This is the largest body cavity of the animal’s body and accommodates various organs from various systems.
• Pelvic cavity: It is small but one of the most important cavities of the animal’s body.

However, you might also learn the following different minor cavities from the animals –

• Nasal cavity of animals: Let’s see the description from a cow’s nose anatomy,
• Mouth cavity of animals: For example, the cavity of a cow’s mouth contains 2 parts and various organs like teeth, tongue, lip, gum, and palate.

Figure 2 highlights some of the common features of each cavity of the animal’s body.

According to the figure, the animal’s body cavities have the following –

• They have start and end points; that means they have specific boundaries.
• All these cavities have small or large spaces.
• Each cavity contains organs, parts of organs, or both, and protects them.

Why are the body cavities important in animals?

Suppose you want to learn or describe the cow’s stomach anatomy. You might first learn or describe its location within the body (Figure 3).

However, you might say this organ (cow’s stomach) is located in the abdominal cavity. Thus, it draws attention to this specific area and is considered the first part of describing its anatomy.

So, to learn or describe the exact position of any specific visceral organ, knowledge of cavities is essential.

At the same time, suppose you are describing the course of the cow’s esophagus. It courses from the neck and enters the thoracic cavity (Figure 3)

However, it passes the boundary of the thoracic cavity and opens into the stomach, which is located in the abdominal cavity.

Thus, you might have an idea of the limit or boundary of these two cavities. These might help you to describe the course of the cow’s esophagus perfectly.

So, cavities are important to describe the courses of animals’ organs/structures, vessels, and nerves.

Now, I will describe the boundaries and contents of all the 4 major body cavities in an animal. For example, I will use the cow, horse, and dog’s body to explain these four major cavities.

Cranial cavity of the animals

The animal’s cranial cavity encloses the brain, along with its coverings and vessels. Figure 4 presents the oval, elongated, irregular cranial cavity within the animal’s skull.

Thus, the cavity is formed by the cranial group of the bones of the animal’s (cow, sheep, goat, horse, dog) skull. However, the cranial cavity of the animal has a roof, a floor, the lateral walls, and the dorsal and ventral extremities.

Roof of the cranial cavity: The roof, also known as the dorsal wall, is formed by the frontal, parietal, and occipital bones. However, it extends from the ethmoidal fossa to the dorsal border of the foramen magnum.

Floor of the cavity: It is formed by the basilar part (base) of the occipital and sphenoid bones. In the middle, it presents a depression, the hypophyseal or pituitary fossa (sella turcica).

Right and left lateral walls: They are formed by the vertical part of the parietal, temporal, and frontal bones, and the orbital wing of the sphenoid. However, they are highly concave to make the cavity for the bulk of the cerebrum anteriorly and cerebellum posteriorly.

Ventral extremity: This is also known as the anterior wall, which is formed by the ethmoid and sphenoid bones. It lodges the frontal and olfactory parts of the cerebrum.

Dorsal extremity/posterior wall: It is formed by the occipital bone and the larger foramen magnum.

Contents and compartments of the cranial cavity

Contents: The animal’s cranial cavity contains the brain, its covering called meninges, and various vessels.

Compartments: The cranial cavity has three compartments – olfactory/ventral, cerebral/middle, and cerebellar/dorsal. Figure 5 shows the three compartments of the animal’s cranial cavity.

Olfactory compartment: It is formed by the sphenoid and ethmoid bones of the animal’s skull. This compartment accommodates the olfactory bulbs and a small part of the cerebrum.

The sharp osseous crista galli separates the two ethmoid fossae that form the rostral limit of the cranial cavity. However, the ethmoid fossae lodge the olfactory bulbs of the cerebrum of the animal’s brain.

The osseous tentorium cerebelli forms the dorsal limit of the animal’s cranial cavity. However, it gives attachment to the membrane of the tentorium cerebelli (Figure 6)

Cerebral compartment: It is the widest and largest compartment of the cranial cavity. However, it is formed by the frontal, post-sphenoid, temporal, and parietal bones.

It extends from the osseous tentorium cerebelli to the level of the junction between the sphenoid and occipital bones. However, its floor is formed by the post-sphenoid bone that contains the pituitary fossa (Figures 4 and 5).

Cerebellar compartment: This smaller compartment is formed by the occipital and temporal bones.

• Floor: It is formed by the basioccipital bone.
• Roof: The squamous part of the occipital bone forms the roof of the cerebellar compartment.
• Lateral walls: They are formed by the petrous part of the temporal bones.

This cerebellar compartment contains the cerebellum, pons, and medulla oblongata. However, the medial part of the petrous temporal bone is marked by the opening of the internal acoustic meatus.

Animal thoracic cavity

The thoracic cavity of the animal is a laterally compressed cone-shaped space within the thorax. Figure 7 shows the animal’s thoracic cavity with an oblique, concave base directed posteriorly.

Here, the figure also shows that the anterior part of the thoracic cavity is compressed. In contrast, the caudal part of the animal’s thoracic cavity is wider.

However, the cranial cone is called the thoracic inlet, or apex, of the thoracic cavity. The caudal wall, or base, is also known as the thoracic outlet.

Now, I will describe the boundaries (dorsal, ventral, anterior, posterior, and lateral) of the animal’s thoracic cavity. You can use a similar strategy to describe the boundaries of the other cavities of the animal’s body.

Boundary of the thoracic cavity

Thoracic inlet/apex: The thoracic inlet of the animal’s thoracic cavity is narrow, nearly oval or triangular in form. It is directed cranially and bounded by the following structures –

• Dorsally: by the first thoracic vertebra.
• Ventrally: by the first sternebra or manubrium sterni of the sternum.
• Laterally: by the first pair of ribs.

Here, the thoracic inlet is occupied by the longus colli muscles of the neck, esophagus, trachea, vessels, and nerves.

Thoracic outlet/caudal wall: So, the thoracic outlet is formed by the diaphragm. However, it slopes downward and forward and is bounded by the following –

• Dorsally: by the last thoracic vertebra.
• Ventrally: by the xiphoid cartilage of the sternum.
• Laterally: by the last pair of ribs and costal arch (Figure 8)

Dorsal wall/roof: The dorsal wall is formed by the thoracic vertebrae, the proximal end of the ribs, and different muscles. Among different muscles, longissimus dorsi, levator costarum, and multifidus dorsi are important. All these are the muscles of the thorax of the cow’s muscular system.

Ventral wall/floor: The floor of the animal’s thoracic cavity is formed by the sternum, costal cartilages, muscles, and ligaments. Here, the muscles involved in forming the floor are transversus thoracis and pectoralis.

Lateral walls: The right and left lateral walls of the thoracic cavity are formed by the ribs and intercostal muscles. However, other muscles supporting the thoracic wall externally and internally also help form the lateral walls.

Contents of the animal’s thoracic cavity

The width of the thoracic cavity is greater at the level of the ninth rib. However, the wall of the thoracic cavity is internally lined by the serous membrane called pleura.

Contents: Figure 9 shows the contents of the animal’s thoracic cavity.

Thus, the contents of the animal’s thoracic cavity are –  

• Organs: Lungs, heart, and part of the esophagus and trachea.
• Vessels and others: Beginning of the larger vessels, nerves, and lymph nodes.

Abdominal cavity of the animals

The abdominal cavity is the largest of the three cavities of the body of an animal. Figure 10 presents the extension of the animal’s abdominal cavity from the musculo-membranous diaphragm to the pelvic inlet.

Thus, the abdominal cavity is separated from the thoracic cavity cranially by the diaphragm. However, this cavity is continued caudally with the animal’s pelvic cavity.

Here, the line of demarcation between the abdominal and pelvic cavities is the pelvic brim/inlet. However, the abdominal cavity of the animal is ovoid in form and somewhat compressed laterally.

The greatest dorsoventral diameter of the abdominal cavity is at the level of the first lumbar vertebra.  Here, the above figure also shows that the abdominal cavity divides into 2 distinct parts:

• Thoracic part of the abdominal cavity: It extends from the diaphragm to the last rib, and
• Abdominal cavity proper: It extends from the last rib to the pelvic inlet.

Now, I will describe the boundaries of the animal’s abdominal cavity as done before in the thoracic cavity. Like the thoracic cavity, this cavity also presents the thoracic inlet, outlet, roof, floor, and lateral walls.

Boundaries of the abdominal cavity

Inlet or anterior wall: Here, the anterior or cranial wall of the abdominal cavity is formed by the concavity of the diaphragm. Thus, it greatly increases the size of the abdominal cavity toward the thorax.

Outlet or posterior wall: It is bounded by the pelvic inlet.

Dorsal wall/roof: The roof of the animal’s abdominal cavity is formed by the lumbar vertebrae, lumbar part of the diaphragm, and sublumbar muscles.

Ventral wall/floor: Here, the floor of the abdominal cavity is formed by the two straight muscles of the abdomen. However, the aponeuroses of the oblique and transverse abdominis muscles, abdominal fascia, and xiphoid cartilage also help form the floor.

Lateral walls: They are formed by the external and internal obliquus and transverse abdominis muscles (Figure 11). However, abdominal fascia, central part of the ilia, cartilage of the sternal ribs, and parts of the caudal ribs also form the lateral walls.

Contents and apertures of the animal’s abdominal cavity

Figure 12 shows the various organs from the animal’s abdominal cavity. It also shows five different apertures/foramina of the abdominal walls.

Contents: The major contents of the animal’s abdominal cavity are – stomach, liver, pancreas, spleen, small intestine, kidneys, part of the large intestine, and ureter.

Apertures: The abdominal walls of the animal’s abdominal cavity are pierced by five foramina or apertures. Three of these are in the diaphragm and named as hiatus esophageus, hiatus aorticus, and hiatus vena cava. The other two apertures (Figure 13) are in the floor of the abdominal cavity (right and left ventral apertures).

Animal’s pelvic cavity

The animal’s pelvic cavity is the smallest of the visceral cavities. Figure 14 shows the pelvic cavity, which is continuous with the abdominal cavity in front.

Like the thoracic and abdominal cavities, the pelvic cavity also has the inlet, outlet, roof, floor, and lateral wall. Thus, I will describe these boundaries of the animal’s pelvic cavity with their contents.

Boundaries of the pelvic cavity in animals

Pelvic inlet: The pelvic inlet of the animal’s pelvic cavity is the oval, elongated entrance. The following structures bound it –

• Dorsally: by the base of the sacrum bone.
• Ventrally: by the cranial border of the pubis bone (part of the pelvic bone).
• Laterally: by the iliopectineal lines of the pelvic bones.

Pelvic outlet: The pelvic outlet is the posterior limit or wall of the pelvic cavity. However, this outlet is bounded by the following structures –

• Dorsally: by the third coccygeal vertebra.
• Ventrally: by the ischial arch of the ishicum bones.
• Laterally: by the caudal edge of the sacrotuberal ligament and the semimembranosus muscles of the hind limb.

Dorsal wall/roof:  The roof of the pelvic cavity is formed by the sacrum and first three coccygeal vertebrae (Figure 15)

Ventral wall/floor: It is formed by the pubic and ischium bones of the pelvis.

Lateral walls: Parts of the ilium bone and the sacrosciatic ligament form both lateral walls of the animal’s pelvic cavity.

Contents of the animal’s pelvic cavity

Figure 16 presents the major contents of the animal’s pelvic cavity. I created this figure of the pelvic cavity using a combination of a hand-drawn diagram and real pictures.

However, the organs contained in this pelvic cavity of the animals include –

• Digestive organs: Parts of the large intestine.
• Urinary organs: Parts of the ureter and urinary bladder.
• Structures: It includes the various nerves, vessels, and muscles.

FAQ’s on the animal’s body cavities

Conclusion

Therefore, knowledge of animal body cavities is required to learn the location of different viscera. The major body cavities of the animals are cranial, thoracic, abdominal, and pelvic.

However, three of these cavities (thoracic, abdominal, and pelvic) are considered visceral cavities. The boundaries of each body cavity contain the roof, floor, anterior wall, posterior wall, and two lateral walls.

References

• Ghosh, R. K.: Primary veterinary anatomy, 2nd Edn.Current Books International, Kolkata.
• Kershaw, D.R. (1983). Animal body cavities. Springer, Dordrecht.
• Rowen D. Frandson, W. Lee Wilke, and A. Dee: Anatomy and physiology of farm animals, 4^th edn.Wiley-Blackwell, USA.
• Getty, R. Sission and Grossman’s The anatomy of the domestic animals, 5^th Edn. W. B. Saunders and Co. Philadelphia (USA).
• Sturdy, L., & Erickson, S. (2022). The language of the terminology. Open Education Alberta.  
• Nickel, R., Schummer, A. and Seiferle, E.: The anatomy of domestic animals, 1^st Edn. Verlag Paul Parey, Berlin.
• Hermanson et al., Miller and Evan’s Anatomy of the dog, 5^th Edn. Elsevier.
• McLeod, W. N.: Bovine anatomy, 2^nd Edn. Burgess Publishing Co. Minneapolis.
• Dyce, K. M., W. O. Sack and CSG Wensing: Textbook of Veterinary Anatomy, Lea & Febiger. Philadelphia
• (n.d.). Section 3: Body Cavity Evolution. An Introduction to Invertebrate Ecology, Taxonomy, and Physiology. BYU-I Books.

Written by