Almost everyone has wondered how many bones there are in a rat. The good news is that the answer is pretty simple. There are only eight bones in a rat’s skeleton, all of which are found in the front and back parts of the rat’s body. This includes the scapula and the clavicle of the pectoral girdle, the vertebral column (spine), and the tibia and fibula.
axial skeleton
Using a skyscan 1072 Micro-CT scanner, I evaluated marsupial vertebral ossification. The ossification of vertebrae is a matter of both genus and species and is highly variable. Among the more notable is the xenarthran, a family of arboreal mammals with a large number of ribless neck vertebrae.
The ossification of the vertebral column is a complex process. The first ossification takes place at the cervical vertebrae. Then, the distal sacral and caudal vertebrae are the last elements to undergo ossification. The ossification process is highly dependent on fetus age. The presumption is that a young fetus is more likely to experience reduced ossification, as compared to an older fetus.
sesamoid skeleton
Traditionally, sesamoids have been considered accessory bones. However, they have been shown to have a functional role in the gliding mechanism. Specifically, they increase the mechanical advantage of the muscle at the joint. They may also protect tendons and reduce friction. In fact, they may serve as fulcrum points along tendon insertions. In addition, their location may be due to local force perturbation.
This study examined the structure and function of normal murine metapodophalangeal sesamoids. It also reexamined the developmental timeline for mineralization.
The sesamoid bone is a type of small nodular bone composed of cartilage elaborated by chondrocytes. It forms within the posterior tibial tendon.
vertebral column (spine)
Depending on the species, the number of bones can vary. The number of vertebrae is also variable. Some species, such as the dog, may have as many as six cervical vertebrae, whereas other mammals, such as the mouse, may have only five. The number of bones may also be determined by the sex of the animal. Generally speaking, males have more bones than females.
The axis cerebellum may be the most voluminous of the bones, with a total of four cerebellar lobes, including one in each hemisphere. The brain may also be large in size, owing to the presence of the thalamus and other important limbic structures.
tibia and fibula
Counting a rat’s ribs is like dividing a banana by two. They are paired and attached to each other, just as they are in human beings. The cisterna chyli is a small dorsal abdominal organ that forms part of the thoracic duct, a system of lymph vessels that unite to form two main ducts. The thoracic duct consists of two small ducts, the first opening into the right superior vena cava, and the other into the junction of the left subclavian and jugular veins.
The tibia is a long bone that consists of several long bones. It is the largest and most complex bone of the forelimb and a crucial part of the pectoral fin and the elongated flat bone of the tail. It also connects the carpus to the first phalanges of the digits.
scapula and clavicle of pectoral girdles
Unlike humans, a rat has only two pairs of vertebrae. These are the cervical and thoracic vertebrae, which are connected to each other by an intervertebral disc. They form the axial skeleton of the body, which provides support for the spinal cord and aorta. They are also used for middorsal support of the abdominal cavity.
The axial skeleton also contains the vertebral column, which is a stacked structure of five or six lumbar vertebrae. Its lateral edges are rounded and its back is shaped like a trapezium. It has a bar of cartilage, which is contained within the connective tissue of its first ridge.
nipples and mammary glands in female mice
Normally, female mice have two pairs of mammary glands on the abdominal region and three pairs on the thoracic region. However, these numbers are variable, and a few strains have more pairs. Female mice normally have five pairs of nipples, and in female rats, there are also an additional abdominal pair.
The nipples are formed through invagination of epidermal cells. A nipple is defined by the presence of thickened skin, surrounded by a primary duct that opens through the tip of the nipple. In virgin females, the nipple is usually obscured by hair except in infant mice.
A fully developed mammary gland consists of secretory aveoli embedded in fat pads. Each pad is a separate unit that branches from the primary duct. The ducts are lined with cuboidal cells.