PECTORAL GIRDLE-REPTILE-BIRD-MAMMAL- COMPARATIVE ANATOMY
The pectoral girdle is connected to the vertebral column through muscles and ligaments. The pectoral girdle consists of two similar halves and each half is formed by three bones namely dorsal, ventral and antero ventral. The dorsal bone is known as scapula, the antero -ventral bone is called clavicle and the ventral bone is the coracoid.
At the junction of tne scapula and coracoid, there is a depression (concavity) which is known as glenoid cavity into which the head humerus of the forelimb anticulates. The same bones are present in all the pectoral girdles of the different vertebrates but have undergone modification.
| Calotes (garden lizard) 1. Girdle is well developed. | Columba (Pigeon) 1. Girdle is well developed for fliqht. | Oryctolagus (Rabbit) 1. Girdle is reduced. |
| 2. The two halves of the girdle are united mid-ventrally by cartilage-nous sternal plate. | 2. The two halves of the girdle are broadly separated. | 2. The two halves of the girdle are broadly separated. |
| 3. Each half of the girdle is known as os in-nominatum. Os inno-minatum is formed by scapula, Suprascapula, coracoid and epicoracoid bones. | 3. Each half is chiefly formed by the scapula, coracoid. The suprascapula is absent. | 3. Each half is chiefly formed by the scapula. The supra scapula and coracoid bones are reduced. |
| 4. The glenoid cavity is formed between the coracoid and scapula. | 4. Same as in calotes. | 4. The glenoid cavity is formed by the scapula bone alone. But the coracoid is attached to it as a process. |
| 5. Comparatively the scapula is smaller. It is in the form of a flattened and curved articulating ventrally. | 5. The scapula is long and blade-Eke. It is sabre-shaped bone extending dorsally over the ribs and articulating anteriorly with the coracoid. | 5. The scapula is the largest bone. It is flat and triangular with broad base directed downwards and narrow apex upwards. |
| 6. Spinous ridge is absent. | 6. The scapula extends internally into an acromion process. | 6. A spine extends along the entire surface of the scapula dorsally. It increases in height towards the apical end and divides into acromion and meta-cromion processes. |
| 7. Cartilagenous suprascapula is a broad, flat and almost rectangular in shape. Dorsally it possess fenestrae. 8. On the ventral side the coracoid bone is flat and have two perforatious- coracoid fenestrae. | 7. Suprascapula is absent. 8. The coracoid bone is stout and pillar-like coracoid fenestrae are absent. | 7.Suprascapula is much reduced and is in the form of thin strip of cartilage. 8. The coracoid bone is reduced and represented by a small coracoid process which is fused with the scapula. |
| 9. The coracoid bone is differentiated into epicoracoid, mesocor-acoid and coracoid proper. | 9. Epi coracoid and Meso-coracoid are absent. | 9. No such parts are seen since the coracoid is highly reduced into a coracoid process. |
| 10. The two clavicle bones are curved, flat, bony rods. These are separated mid ven-trally by a T- shaped interclavicle. | 10. Clavicle bones are thin and attached dorsally to the scapula bones. These two are fused distally with the interclavicle to form furcula or Merry thought bone or wish bone. | 10. The two clavicles are rod-like and attached to the sternum. Interclavicle is absent. |
| 11 .Foramen of triosseum is absent. 12. Rhomboidai plate like sternum is present and its anterior is connected to the distal er.d of inter clavicle. | 11. At the junction of coracoid, scapula and clavicle bones foramen of triosseum is present. 12. Sternum is a separate bone with a keel along the mid ventral for the attachment of flight muscles. | 11. Foramen of triosseum is absent. 12. A six segmented elongated bony rod-like sternum is present mid ventrally to which ribs are attached. |