82 VERTEBRATE ZOOLOGY 



Observe the muscles on the dorsal side of the arm and shoulder 

 on the right side of the body. Determine accurately the outlines 

 of the coracoid and the procoracoid beneath the muscles. The out- 

 lines of the scapula will also be easily determined by moving the 

 arm back and forth. Pass a scalpel beneath the different parts of 

 the girdle on this side and remove both girdle and leg from the 

 trunk, taking care not to injure them. 



Carefully remove the muscles from the girdle and identify the 

 three parts and the glenoid cavity (in which the humerus articu- 

 lates). Note the foramen coracoideum, a small hole through which 

 a nerve passes. 

 Exercise 18. Draw the pectoral girdle. 



Remove the muscles from the arm, but do not separate its 

 bones from one another. The skeleton of the arm is made up of 

 three divisions,— a proximal, a middle, and a distal. The proxi- 

 mal division, or the upper arm, is a single bone,— the humerus,— 

 the articular ends of which are cartilaginous ; its proximal end, or 

 head, articulates with the glenoid fossa. Note the difference in the 

 form of the articular surfaces of the two ends. The middle di- 

 vision, or forearm, is composed of two bones,— the radius and 

 the ulna,— the ends of which are cartilaginous. Of these the radius 

 is anterior, or preaxial, in position ; the ulna is postaxial and is 

 prolonged at its proximal end to form the olecranon process, which 

 forms the elbow. 



The distal division includes the wrist and hand. The wrist, or 

 carpus, is composed of six small cartilages, two of which form a 

 transverse proximal row, three a distal row, while one is in the 

 center. In the typical vertebrate carpus three bones form the 

 proximal row, five the distal row, and one or two are in the center. 

 In the hand of Necturus four digits are present, each of which is 

 composed of a proximal bone called the metacarpal and two or 

 three distal bones called the phalanges or finger bones. In the 

 typical vertebrate hand five digits are present, the digit which is 

 lacking in the hand of Necturus being the first, or thumb. 



Exercise 19. Draw the arm on a scale of 2 or 3, showing accurately 

 the outline of each bone and cartilage. 



