Cervicals (atlas, axis, CE3-CE7)
There are a total of 7 cervical vertebrae in a bison skeleton. Due to the specialized shape and functions of the first two cervicals, they are given separate names -- the atlas (CE1) and axis (CE2). The atlas articulates with the occipital condyles of the cranium with the deeply concave cranial articular cavity. The axis has the distinctive dens at its cranial surface to allow rotational articulation with the atlas.
The next three cervical (CE3, CE4, and CE5) are similar in shape, but all exhibit typical cervical attributes that make them easy to identify:
very rounded, nearly hemispherical articular surfaces on the centrum or body (as with all vertebrae, the convex articular surface is toward the animal's head (cranial) and the concave on the caudal surface.
two transverse foramen that parallel the vertebral foramen.
widely spaced, flattened articular processes (the articular surfaces on the cranial processes are dorsally directed, and those of the caudal processes are ventrally directed.
The sixth (CE6) and seventh (CE7) cervicals are readily identifiable. CE6 shares all of the general cervical characteristics listed above, but also has distinctive, ventrally directed rectangular/lobate transverse processes. C7 is sometime misidentified as a thoracic because of its longer dorsal spinous process. It has the widely spaced articular processes at both the cranial and caudal surfaces, which is different from all thoracics. It also has costal pits (for articulation with the head of the first rib on its caudal surface (no costal pits on the cranial surface).
There a total of 14 thoracic vertebrae in the average bison skeleton. These are the vertebrae that form the hump, which provides attachments for the powerful muscles of the bison's neck.
There are several characteristics that allow you to recognize thoracic vertebrae:
costal pits (for articulation with rib heads) on both the cranial and caudal surfaces of the centrum (the exception to this is the 14th thoracic, which only has costal pits on its cranial margin) -- when looking at the centrum of a thoracic you may recognize Mickey Mouse (the centrum is the head, and the costal pits are the ears).
larger dorsal spines, especially on the first 10-11 thoracics., but don't let this be your primary method of identification because (a) dorsal spines are often missing, (b) the last thoracics have very short spines like the lumbars, and (c) remember that the 7th cervical also has a large dorsal spinous process.
closely spaced, flattened articular surface on the cranial and caudal margins of the dorsal spine (exceptions to this are the last several thoracics that have articular processes more like the 'hooked' processes on the lumbars).
The typical bison has 5 lumbar vertebrae. There are several characteristics that allow you to recognize lumbars:
the have the broad, flat transverse processes (lumbars look like Star Fighter planes with the transverse processes being the wings)
the articular surfaces of the centra are the flattest of the bison's skeleton (they have no costal pits).
the articular processes are noticeably 'hook-like' and provide a very solid connection between the lumbars allowing very little movement.
Ribs, strenabrae, and costal cartilage
There a total of 28 ribs in a complete bison skeleton (2 for each thoracic). There are 6-7 stenabrae in the bison with the cranial most being the manubrium and the caudal most being the xiphoid. Ossified costal cartilage connects the distal ends of the ribs to the sternum.
In a skeletally mature bison, the 5 sacral elements are fused into a solid sacrum. The wings of the sacrum contact the ilium of the os coxae and provide the point of union between the axial skeleton and the rear limb. The caudal vertebrea form the tail and there are 15-18 in a bison.
you can click on regions of the axial skeleton to view labeled photos of the bones
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