Page 124 - ShowSight - September 2020

FORM FOLLOWS FUNCTION
“ pictured above: Figure 6. First Cervical Vertebrae, the Atlas
PAIRED WITH THE ATLAS’ ‘YES’ MOVEMENT,
pictured right: Figure 7. Second Cervical Vertebra, the Axis
”
The most obvious purpose of the neck is to sup- port and allow for the movement of the head. The vertebrae also protect the spinal cord, starting with the cervical vertebrae. But there is much more going on with the neck than the eye can see. Let us take a closer look at the dog’s neck.
The neck has two specialized vertebrae: the Atlas and the Axis. The Atlas is the first cervical vertebra. It has a small body (B) with two wings (W—trans- verse processes). The Atlas articulates (see Figure 6) with the head at the occiput (see Figure 1) and is responsible for the up-and-down movement of the skull on the neck, often called the “Yes” movement or “Yes” joint.
The second cervical vertebra is the Axis, which provides the side-to-side and rotary motion of the skull. Paired with the Atlas’ “Yes” movement, the Axis is called the “No” joint of the skull (see Figure 7).
The articulation of the Axis (darker vertebra) with the Atlas (light vertebra) provides for the movement of the skull (see Figure 8).
The neck is held up by a cervical ligament (nuchal) that extends from the spinous process of the axis to the withers at the first thoracic vertebra. This ligament is unusual in that it can both contract and expand. It contracts to pull the neck up and relaxes to allow the head to be lowered. Ligaments attach bone to bone, whereas tendons attach muscle to bone. Muscles pull the tendons and tendons pull the bones (see Figure 9). The nuchal ligament is a strong influence on the form of the topline of the neck.
The most powerful muscle of the neck is the bra- chiocephalicus muscle, which reaches from the neck to just below the shoulder joint where it attaches at the upper arm. This muscle activates the movement of the shoulder blade. Other smaller muscles extend from the shoulder blades to the vertebrae of the neck (see Figure 10).
Muscles produce movement only when they con- tract. Muscles are almost always arranged in oppos- ing groups that perform opposite actions on any
given joint. Dogs with a high head carriage (Poodles, Afghan Hounds and Min- Pins immediately come to mind) are those in which the neck muscles are tightened due to the head carriage, pulling the leg forward and higher, resulting in a springy or prancing gait. The higher head position leads to even more lift to the front feet when in motion—correct movement in these breeds.
In most breeds, the length of the neck and the length of the head are approxi- mately the same (see Figure 11). Since the shoulder blade muscles are attached to the neck, an arched neck (like an arched doorway) is structurally stronger and is better at withstanding the pulling forces generated from the shoulder blade muscles.
A “ewe neck” lacks this arch, and the circumference where the neck joins the body is about the same as at the head (see Figure 12). The ewe neck has no arch at the crest of the neck and is concave, plus the neck is rather abruptly joined to
pictured above:
Figure 8. Articulation
Axis and Atlas
pictured left:
Figure 9. Nuchal Ligament
the Axis is called the ‘No’ joint of the skull.
122 | SHOWSIGHT MAGAZINE, SEPTEMBER 2020