id="ulink_f6541787-9e80-50a2-b960-e0421babce86">The cranium is the portion of the skull that encases the brain. The mandible and maxilla are two significant facial bones. The mandible forms the lower jaw, and the maxilla forms the upper jaw. The eye sockets in the skull are known as the orbits (Figure 3.7).
Figure 3.7 Cranium.
Source: Courtesy of Jennifer Smith, LVT.
The hyoid bone (also known as the hyoid apparatus) is made up of several parts that may be cartilage or bone. It is a U‐shaped structure that is located above the larynx and below the mandible and is suspended by ligaments.
Ribs are pairs of flat, curved bones that attach dorsally to the thoracic vertebrae. The cartilage at the end where the rib attaches to the sternum is called the costal cartilage. The sternum is also known as the breastbone, and it forms the ventral midline of the rib cage. The ribs that are not attached to cartilage are known as floating ribs. Cats and dogs have 13 pairs of ribs.
The vertebral column is also known as the backbone and is made up of numerous vertebrae. There are five different types of vertebrae, and there are variations among species in the number of each different type. Here, we focus on the number of vertebrae in canine and feline patients.
The main functions of the vertebral column, also known as the spinal column, are to support the head and body and to protect the spinal cord. The vertebral column is made up of individual bones called vertebrae.
The cervical vertebrae are the vertebrae of the neck. There are a total of seven cervical vertebrae in all domestic mammals. The first one is called the atlas and the second one is called the axis. The thoracic vertebrae are the vertebrae of the chest. The ribs are attached to these vertebrae. There are 13 thoracic vertebrae in the cat or dog. The lumbar vertebrae are the vertebrae of the lower back. There are a total of seven in cats and dogs. The sacral vertebrae (also known as the sacrum) consist of three fused vertebrae to which the pelvis is attached. Finally, the coccygeal vertebrae are the vertebrae of the tail, and the number of coccygeal vertebrae can vary between six and 23 depending on the species and whether the tail has been docked.
Vertebral formulas are written in a specific format and vary from species to species (Figure 3.8). For example, the dog or cat vertebral formula would look like this:
C‐7, T‐13, L‐7, S‐3, Cy 0‐23
Appendicular skeleton
As mentioned above, the appendicular skeleton is composed of the bones of the limbs, clavicle, scapula, humerus, radius, ulna, carpus, metacarpals, pelvis, femur, patella, tibia, fibula, tarsus, metatarsals, and phalanges.
Figure 3.8 Vertebral formula.
Source: Courtesy of Jennifer Smith, LVT.
Bones of the forelimb
Bones of the forelimb can vary depending on the species. The clavicle is also known as the collarbone and is a skinny bone that connects the sternum to the scapula. Not all species have a clavicle. The scapula is also known as the shoulder blade and is a triangular‐shaped bone located on the side of the thorax. The humerus is the long bone of the forelimb that extends from the shoulder to the elbow. The ulna and radius are located distal to the humerus. The radius is the cranial long bone of the forelimb that runs from the elbow to the carpus, and the ulna is the caudal long bone of the forelimb that runs from the elbow to the carpus.
Just distal to the radius and ulna is the carpus which consists of the joint and several carpal bones. The carpal bones are two rows of irregularly shaped bones.
The metcarpals are long bones found just distal to the carpus. The number of metacarpals varies among species. Dogs have five metacarpal bones.
The most distal part of the forelimb are the phalanges. Phalanges are the bones of the digit. Digits relate to human fingers. The number varies in animals (Figure 3.9).
Bones of the hindlimb
The types and number of bones of the hindlimb can vary depending on the species. The information below refers to domestic animals such as dogs and cats.
The bones of the hindlimb consist of the pelvis, femur, patella, tibia, fibula, tarsus, metatarsals, and phalanges.
The pelvis and the coccygeal vertebrae articulate with the sacrum. The acetabulum is the hip socket in which the head of the femur sits. The femur is the longest bone in the body and is located just distal to the pelvis. The stifle is the joint located between the femur and the tibia. The patella is a large flat bone that is located over the stifle joint. In humans, this is referred to as the knee cap. Just distal to the patella are the tibia and fibula. The tibia is the larger of the two bones and is considered the more weight‐bearing bone, and the fibula is a long, thinner bone.
Figure 3.9 Bones of the forelimb.
Source: Courtesy of Jennifer Smith, LVT.
The tarsus is located distal to the tibia and fibula and consists of numerous, irregularly shaped bones that are arranged in several rows. In humans, the tarsus is known as the ankle.
The metatarsals are the long bones found just distal to the tarsus. Similar to the metacarpals in the front leg, the metatarsals will vary among species. The most distal part of the rear limb are the phalanges. Phalanges are the bones of the digits (Figure 3.10).
Now that you are familiar with all the basic bones in the dog and cat and the basic directional terms, let’s put them into use. For practice, use the information you learned above to complete the activity below.
1 The skull is ‐‐‐‐‐‐‐‐‐ to the pelvis. (cranial/caudal)
2 The femur is ‐‐‐‐‐‐‐‐‐ to the tarsus. (distal/proximal)
3 The ‐‐‐‐‐‐‐‐‐ is also known as the breastbone.
4 The
