32 ANATOMY OF THE RAT 



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; medi- 

 ally 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 proxi- 

 mal 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 articu- 

 lates with the head of the radius. The olecranon is the 

 stout projection behind the semilunar notch for the inser- 

 tion 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. 



