Clavicle or collarbone

Like humans, rats have clavicles. It is a long bone that serves as a strut between the shoulder blade and the sternum or breastbone. It forms, together with the scapula, the shoulder girdle or pectoral girdle. The pectoral girdle connects the arm to the axial skeleton on each side.

It can be divided into three parts: medial end, lateral end and shaft.

The Medial end articulates with the clavicular notch of the manubrium of the sternum to form the sternoclavicular joint. The lateral end is flat and bears a facet for attachment to the acromion process of the scapula, forming the acromioclavicular joint

The Scapula or shoulder bone

In humans, the scapula or shoulder blade is the bone that connects the humerus with the clavicle. With rats the connection with the clavicle isn't that straight forward: the connection is a joint venture of named bones with the head of the humerus. Like their connected bones the scapulae are paired, with the scapula on the left side of the body being roughly a mirror image of the right scapula. The scapula has a lot of muscles attached to it. Those will be discussed in a later tutorial.

Humerus or upperarm bone

The humerus is the bony constituent of the upper arm. Its proximal end articulates with the scapula ; it articulates distally with the radius and ulna of the fore arm. Between these two extremities is the shaft, or body, of the bone. The head is a prominent oval enlargement at the proximal end. The deltoid tuberosity is a very prominent rough-edged ridge running, on the ventral surface, from the greater tuberosity about half way to the distal end of the humerus. The articular surface at the distal end of the bone is saddle-shaped to receive the corresponding surfaces of the radius and ulna. This end of the bone is flattened. It bears two depressions immediately above the articular surface.


The radius and ulna support the fore arm, the radius lying anterior. The two are firmly bound together by the interosseus ligament. The body of the radius bows forward and outward. Dorsally it expands abrubtly, forming the head which bears an oval surface for articulation with the humerus. The posterior side of the head is flattened and rests against a similar surface of the ulna. The Radius is expanding distally to articulate with the wrist or carpal bones. The elbow joint, where radius and ulna meet the humerus, is of the hinge type, which permits only of extension and flexion of the arm.


The ulna is laterally compressed, the lateral surface bearing a pronounced groove extending from the level of the head of the radius two-thirds of the way to the distal end. Like the radius, the ulna bows forward and outward, so that an articulated skeleton looks "bow-legged." The ulna terminates distally in the conical, blunt styloid process for articulation with the wrist bones. The semilunar notch is the saddle-shaped depression near the proxi-mal end, which, with the head of the radius, articulates with the humerus. The fiat surface at its ventral border corresponds to the radial notch, of other animals; it articulates with the head of the radius. The olecranon is the stout projection behind the semilunar notch for the insertion of the extensor muscles of the upper arm.

Carpal bones

There are nine carpal or wrist bones. In this model you see only 6 of them (need to update it)

Metacarpal bones

The metacarpal bones are the relatively long bones in the palm of the hand. Counting from the medial side of the manus, the third and fourth are the longest, the fifth is considerably shorter, while the first is so short as to be readily mistaken at first glance for one of the carpal bones.

Phalanges bones

Each digit contains three phalanges, except the thumb (pollex), which contains two. Each terminal phalanx bears a claw, that of the thumb being flattened like a nail.