192 VERTEBRATES. 



II. Bones of the Fore Limb. In the fore limb find the 

 following parts : 



The single long bone of the arm, the humerus. Its shape 

 is characteristic of long bones; therefore note that it is 

 somewhat cylindrical, that it is hollow, and that it has an 

 expanded articular surface at each end, with a shaft between. 



The bone of the forearm, made up of two bones, radius 

 and ulna, which are grown together (anchylosed). 



In the bones of the hand, three series may be distin- 

 guished : 



1. A series of very small, irregularly shaped, carpal 

 bones, immediately succeeding the bones of the forearm. 



2. A single transverse row of cylindrical metacarpal 

 bones. 



3. Several transverse and unequal rows of phalangeal 

 bones, or phalanges, growing successively shorter toward 

 the tips of the digits. 



III. The Shoulder Girdle. Study the pectoral arch, or 

 shoulder girdle. Observe that its bones, together with 

 their attached cartilages, form an incomplete ring around 

 the body, that the two halves of the girdle meet on the 

 median ventral line, and that the parts are obviously 

 arranged for the support of a pair of limbs. 



Observe that each half of the shoulder girdle is com- 

 posed (essentially) of three bones, which meet around the 

 cavity (glenoid fossa) into which the head of the humerus 

 fits. One of these bones (the scapula) extends dorsally, 

 and is supplemented by a broad cartilage on the dorsal 

 surface. The other two extend ventrally to meet their 

 fellows of the opposite side on the median ventral line. 

 The larger posterior one is the coracoid. The slender, 

 anterior one is the clavicle. 



Posterior to the point of union of the two coracoids, 

 a flat bone (the sternum), which does not belong to the 

 shoulder girdle, extends posteriorly on the median ventral 



