LAB 10.1 Poultry skeleton


1. Wing digit 1
2. Wing digit 2
3. Wing digit 3
4. Carpals
5. Radius
6. Ulna
7. Humerus
8. Scapula
9. Thoracic vertebrae
10. Femur
11. Ilium
12. Synsacrum
13. Pygostyle
14. Ischium
15. Pubis
16. Fibula
17. Tibiotarsus
18. Tarsometatarsus
19. Four foot digits
20. Patella
21. Carina of sternum
22. Furcula of 2 clavicles
23. Coracoid
24. Cervical vertebrae

Vertebrae - highly fused
Cervical, n = 14 free
Thoracic, n = 7
to T5 are fused
T6 free
T7 fused to synsacrum (T7 + LS1
to LS14 + C1)
Lumbosacral, n = 14 fused
Caudal, n = 6
The synsacrum = T7 + LS1
to  LS14 + C1

   The skeletons of poultry are radically different from those of the farm mammals. Not only is the avian skeleton adapted for flight, but birds and mammals are only distantly related zoologically.

Skull and neck. The skull has very large eye orbits and a small cranial cavity. The long double curved neck contains 14 cervical vertebrae, and the ring‑like atlas articulates to the skull with only a single occipital condyle. The axis has a large odontoid process that projects anteriorly.

Vertebral column. There are 7 thoracic vertebrae, but numbers 2 to 5 are fused. Thoracic vertebrae 6 can move freely, but the last thoracic vertebra is fused to the synsacrum. The synsacrum is a fused length of the vertebral column that contains thoracic vertebra 7, 14 lumbo-sacral vertebrae, and the first coccygeal or caudal vertebra, but skeletal fusion in the vertebral column does not occur for many weeks after hatching.   There are six caudal vertebrae that, apart from the first, are free and mobile. However, only numbers 2 to 5 are normal vertebrae, since the last one is formed into a three sided pyramidal bone called the pygostyle.
Ribs.  There are seven ribs: the first two are free while the last five are attached to the sternum. There are no costal cartilages. Ribs 2 to 6 each have an uncinate process which overlaps the next posterior rib. The sternum is extremely large.  It has a conspicuous ventral ridge in the midline, the CARINA, which increases the area available for attachment of the flight muscles. The dorsal surface of the expanded sternum is concave and forms the floor of a continuous thoracic and abdominal cavity.

Glenoid (1),  scapula (2), coracoid (3), clavicle (4) and sternum (7).

Wing.   The bones of the fore limb are greatly modified to form the wing (Figure 2‑19). Distal to the humerus are the widely spaced radius and ulna. The carpals, metacarpals and digits are reduced to form a stiff skeletal unit for the anchorage of the primary flight feathers. The three digits of the wing are equivalent to digits 2, 3, and 4 in other animals . The wing articulates with the body at the glenoid cavity which is strengthed by the convergence of three bones, the scapula, the coracoid and the clavicle. In birds the coracoid is a separate bone, whereas in mammals it has been reduced to a small integral part of the scapula. The clavicles of right and left sides are fused ventrally to form the furcula or wishbone. Although many mammals have a pair of clavicles, they are absent in cattle, sheep and pigs. The clavicle functions as a strut to support the shoulder joint in animals which have complete mobility of the shoulder joint. Since cattle, sheep and pigs have cursorial limbs with a restricted fore and aft movement, they do not need clavicles. In poultry, the distal end of the coracoid is braced against the sternum. In flight, the body of a bird hangs from its wings at the shoulder joint, hence the more elaborate support for the glenoid cavity.

Digits 1, 2 and 3;  carpometacarpus (4), radius (5), ulna (6) and humerus (7).
Leg.   In poultry, the legs show many cursorial adaptations. Distal to the femur, the fibula is reduced to leave the tibia as the major bone. In the embryo this occurs as a result of the differential growth and translocation of the distal part of the fibula to become part of the tibia. The proximal tarsal bones are fused to the distal end of the tibia to increase its length, and the whole skeletal unit may be called the tibiotarsus. The distal tarsal bones are incorporated into the proximal end of a single bone, the tarsometatarsus, which also includes the fused metatarsals 2, 3 and 4. Of the four digits which form the bird's claw, digit 1 is directed posteriorly while digits 2, 3 and 4 are anterior. This adpatation enables the bird to perch. The ilium is fused to the synsacrum. Instead of being fused in the midline, the pubic bones are separate, and they project backwards as thin rods. The open structure of the pelvis in the ventral region facilitates the passage of eggs from the body cavity. The ilium, ischium and pubis all contribute to the acetabulum, but the ilium forms more than half of the socket and the floor is membranous .

Digits 1, 2 3 and 4; tarsometatarsus (5), tibiotarsus (6), fibula (7) and femur (8).

Obturator foramen (1), acetabulum (2), sciatic foramen (3), ilium (4), ischium (5) and pubis (6).