90 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



elongated process. The posterior part is the coracoid region, but no ossification 

 has occurred in either of the regions. Dorsally above the joint with the fore 

 limb is a bone, the scapula— the only bone in the girdle. Attached to the dorsal 

 border of the scapula is the suprascapular cartilage. There is no sternum 

 (although two or three pairs of small cartilages found in the ventral wall, 

 located in the myosepta, are regarded as the sternum by some authors) . Note 

 that the pectoral girdle has no connection with the vertebral column. 



The fore limb is similar to the hind limb. The upper arm is composed of the 

 humerus; the forearm of the preaxial radius and the postaxial ulna; the elements 

 of the carpus or wrist are difficult to distinguish (there are six or seven cartilages 

 in three rows); there are four metacarpals in the palm followed by phalanges. 

 The middle segment of the limb is bent and directed ventrally, thus elevating 

 the animal slightly above the ground. 



Draw the pectoral girdle and one fore limb. 



5. The pectoral girdle and sternum of the frog. — In the frog we find that 

 the cartilages present in the urodele girdle have been partially replaced by bone. 

 A sternum is further present in the median ventral line between the ventral ends 

 of the halves of the pectoral girdle. Study the girdle and sternum. The sternum 

 consists of two bones and two cartilages arranged in a longitudinal series and 

 separated into two groups by the pectoral girdle. The anterior group, projecting 

 cranially from the girdle, consists of a terminal rounded cartilage, the epistcrmtm, 

 posterior to which is a bone, the omosternum . The posterior group, projecting 

 caudad from the girdle, is composed of an anterior bone, the sternum proper, and 

 a terminal rounded cartilage, the xiphistcrnum. The ventral part of the pectoral 

 girdle consists of two pairs of bones, their ventral ends meeting in the median 

 ventral line between the two parts of the sternum. The anterior pair of bones 

 is the clavicles. The clavicles are membrane bones which cover and conceal 

 the procoracoid cartilages; these cartilages remain unossified in Anura. The 

 posterior ventral bones of the girdle are the coracoids, ossified from the coracoid 

 cartilages. • The medial ends of the coracoids remain in the cartilaginous condi- 

 tion (forming cartilages which are designated in texts as the epicoracoids, but 

 this term is confusing as it is also used in another connection) . The dorsal part of 

 the girdle consists of two bones on each side : one next to the articulation of the 

 fore limb, the scapula, and a large, thin, flat bone medial to the scapula, the 

 suprascapula, having a cartilaginous border. The girdle is not connected with 

 the vertebral column. The depression which receives the head of the humerus 

 is the glenoid fossa; scapula and coracoid take part in the formation of the glenoid 

 fossa, but the clavicle does not. This indicates that the clavicle is of different 

 origin from the other bones of the girdle. Draw the girdle and sternum of the 

 frog. 



6. The pectoral girdle, sternum, and fore limb of reptiles. — On the skeleton 

 of the turtle observe that a pectoral girdle is present but a sternum is absent. 



