Chapter 6: Appendicular Skeleton
Understand the basic components that comprise the appendicular skeleton in Craniates.
Understand the broad evolutionary forces shaping these elements in a phylogenetic context.
Learn structural differences between the represented classes of Craniates.
The skeletal elements of the appendicular region consist anteriorly of paired pectoral appendages
(fins or limbs) and an associated pectoral girdle, and posteriorly of pelvic appendages and pelvic
girdles in the hip region. The earliest craniates lacked paired appendages and their associated girdles
in both the pectoral and pelvic regions.
This body form is also characteristic of modern jawless
craniates (hagfishes and lampreys).
In early gnathostomes, the pectoral appendages first appeared as
small fins that likely aided in maneuverability and stability of the body. As vertebrates made the
transition to land, these fins evolved into limbs, which were necessary for both body support and
movement. The associated girdles of the shoulder and hip region, while small in fishes, are large
supportive structures that help transfer body weight from the axial skeleton to the appendicular
Chondrichthyes (Use figure 5-2 for identification)
of chondrichthyans are composed entirely of cartilage.
are enlarged, extending dorsally and merging ventrally to form U-shaped bridges. The well-
cartilages of the fins are not dermal, but the ceratotrichia are considered dermal
derivatives. Examine the plastic mounts in the lab; notice the homologous elements of both girdles
with those of other vertebrates. Make sure you can identify the following structures:
process, suprascapula, radial cartilage, ceratotrichia, coracoid bar, metapterygium,
mesopterygium, propterygium, pubioischiac bar, iliac process.
Aquatic Osteichthyes (Use figure 5-3 for identification)
Among extant actinopterygians, the detailed structure of the pectoral and pelvic girdles is highly
diverse. Examine the bowfin (
), a basal actinopterygian fish, and the perch, a fairly
typical derived actinopterygian.
The endoskeletal cartilages remain as the point of appendage
attachment; however, dermal
elements have fused to the pectoral
girdle to add support. The
cleithrum complex (“shoulder” area)
is directed dorsally from the fin, and is variably composed of
several dermal bones. Some of these bones form a connection with the skull and superficially
appear as skull elements. Locate these on the skeletal preparations. The
as in all other gnathostomes. Note that in actinopterygians, unlike in tetrapods, the
pelvic girdle does
attach to the vertebral column.
The structure of the fin itself deserves some attention, and is usually the basis for differentiating