Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/46

32 just below the semilunar notch of the ulna. The radius is expanded distally to articulate with the wrist, or carpal bones. Longitudinal grooves cross this expansion; medially it bears the pointed styloid process.

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 out- ward, 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 semi-lunar notch is the saddle-shaped depression near the proximal end, which, with the head of the radius, articulates with the humerus. The flat 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.

The joint between the humerus and scapula is of the "ball and socket" type, permitting of lateral as well as anteroposterior movement. The elbow joint, however, is of the hinge type, which permits only of extension and flexion of the arm.

There are nine carpal or wrist 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. 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.

Exercise VIII. Draw and label the lateral view of the scapula and the bones of the fore limb.