FORM FOLLOWS FUNCTION
Figure 6. Side View of Vertebrae Showing Intervertebral Disc
Figure 7. The Seven Cervical Vertebrae
Figure 8. The 13 Thoracic Vertebrae
THE CERVICAL VERTEBRAE SUPPORT THE HEAD AND ALLOW FOR ITS MOVEMENT UP-AND-DOWN AND FROM SIDE-TO-SIDE AS WELL AS ENABLE THE DOG TO EXTEND THE NECK FORWARD OR TOWARD THE GROUND.
Between the vertebrae are intervertebral discs that are composed of a compressible substance and are attached to each vertebra, allowing for movement and serving as a shock absorber. During my research, I think the most interesting description of these discs was comparing them to jelly donuts—with the dough being the fibrous covering on the outside of the disc and the inside being the jelly or gelatinous material (nucleus pulposis) serving as the cushioning inside the disc. (See Figure 6.) As a dog ages, the jelly inside the disc becomes chalky and harder. When the disc is damaged due to deterioration or inju- ry, it can leak the jelly-like or hardened interior, which is termed a herniated disc. As the interior is extruded, it compresses the soft tissues and nerves surrounding the disc, causing pain and immobility. When the discs degenerate, the condition is referred to as intervertebral disc disease or IVDD. THE NECK (CERVICAL VERTEBRAE) The canine neck contains seven cervical vertebrae as do all mammals, with only a few exceptions. Think on this for a moment: Mammals, from humans to giraffes, have seven cervical vertebrae. The only difference is in the length of the cervical bones. The cervical vertebrae support the head and allow for its movement up-and- down and from side-to-side as well as enable the dog to extend the neck forward or toward the ground. The first two vertebrae of the neck are unique in their formation and function. The first cervical vertebra is the atlas (“A” in Figure 7), which allows up-and-down
movement (think “yes” movement of the head), and the second is the axis (“B” in Figure 7), which allows the side-to-side or rotary movement asso- ciated with the “no” movement of the head. The Atlas has a smaller body and spinous process, but also has very long, thick transverse processes called “wings of alae,” which are easy to feel in the neck. The wings allow for the attachment of powerful neck muscles from which arises the much-admired arch in the neck of a dog. The atlas attaches to the skull in a unique way and allows for the hinge-like up-and-down movement of the skull on the neck. Most of the cervical vertebrae do not have the high spinous process as shown in the thoracic vertebrae in Figures 3-5. The neck vertebrae tend to be wider in body, with spinous processes that gradually increase in length to the last (7th) vertebra. In some of the larger breeds, the cervical vertebrae are mal- formed, leading to disc rupture and compression of the spinal cord. This is commonly referred to as “Wobblers Syndrome.” THE THORACIC VERTEBRAE There are 13 thoracic (chest) vertebrae. Their primary function is the sup- port of and attachment to the ribs for the vital process of breathing. The longer spinous processes allow for the attachment of the strong neck and back muscles. The first nine thoracic vertebrae have the longest spinous processes, and they all angle back toward the tail of the dog. These verte- brae comprise what is called the “withers” of the dog (most especially the second and third vertebrae, which are the highest). Even more important, the first nine ribs are attached to both the thoracic vertebrae at the top and to the sternum underneath the dog, forming a nearly solid, enclosed unit. The last four thoracic vertebrae, which have tips that are fairly level with one another, form the mid-back of the dog. Some refer to this section as the “true” back, as these four vertebrae are nearly identical in shape to the lumbar vertebrae, but they still fully function as rib-carrying thoracic vertebrae. (See Figure 8.)
98 | SHOWSIGHT MAGAZINE, OCTOBER 2021
Powered by FlippingBook