Closer Look at the Humerus (Upper Arm) of a Dog

Closer Look at the Humerus (Upper Arm) of a Dog

 

Form Follows Function – Closer Look at the Humerus (Upper Arm) of a Dog

 

The forequarter of the dog is responsible for both the steering and braking ability of the animal. It lifts the center of gravity as the dog moves forward, acting somewhat similarly to the pole of the athlete participating in the pole vault. It is also a stabilizing force that opposes lateral displacement and enables the dog to turn on a dime. While the rear propels the dog forward, the forequarter also adds propulsion forward through the gripping action of the front foot on the ground, which pulls the dog forward somewhat while at the same time serving to stabilize the forequarters to allow the driving force of the hindquarters to propel the dog forward over the front assembly (pole vault). The scapula is attached to the thorax by fibrous connective tissue; no fixed joint attaches the forequarters to the thorax (body) of the dog.

While the rear propels the dog forward, the forequarter also adds propulsion forward through the gripping action of the front foot on the ground, which pulls the dog forward somewhat while at the same time serving to stabilize the forequarters to allow the driving force of the hindquarters to propel the dog forward over the front assembly…

In any discussion concerning the dog’s forequarters, much of the emphasis is placed on the scapula (shoulder blade). The positioning on the chest and the degree of layback and proper layon of the scapula does much to determine the forward reach of the canine front leg.

Closer Look at the Humerus (Upper Arm) of a Dog
Figure 1. Forequarters

The humerus (upper arm) is often commented upon concerning its articulation with the scapula to form the shoulder joint. This shallow ball and socket joint can move in any direction, which is why the forelegs may move laterally (winging, paddling, etc.), mainly to waste time when the rear drive exceeds the front reach of the dog. The shoulder joint primarily functions in inflection (bending or drawing the parts together) and extension (the straightening of the limbs). This junction forms the point of the shoulder. (See Figure 2A.) The landmark felt when determining the point of the shoulder (Figure 2B) is the upper point of the humerus.

Closer Look at the Humerus (Upper Arm) of a Dog
Figure 2. Point of Shoulder

The primary function of the humerus is to support the body and provide some force in propelling the dog forward, and it also serves to provide balance to the dog. In most breeds, the humerus is approximately equal in length to the scapula; the major exceptions are found in the achondroplastic (dwarf) breeds.

Many breed standards call for a 90-degree angle of the humerus’ body with the scapula’s spine when the dog is in a normal standing position. Given the landmarks that are most readily discernable by someone without access to an x-ray machine, this is a reasonably accurate way to determine angulation, depending upon which “landmarks” one is using. You can find a great explanation of how to estimate the forequarter angle on pages 98 & 99 of Claudia Orlandi’s book, Practical Canine Anatomy & Movement, which I highly recommend to those who want more in-depth knowledge on the subject. The humerus divides into three sections: the head, neck, and body. (See Figure 3.)

dog Humerus
Figure 3. Humerus

The body or shaft of the humerus is a long, slightly S-shaped bone that enlarges as it nears the junction of the elbow joint. The humerus bone ends as a condyle joint at the elbow. A condyle is shaped somewhat like a pulley, with a deep notch in the center into which the ridge of the upper portion in the ulna bone of the forearm fits to form the most stable portion of the elbow joint.

The elbow is a hinge joint. Therefore, when the forelimb is vertical, the joint is in complete surface contact and can be considered “locked” in place. When the limb is partially extended and when it is retracted, a loosening of the joint occurs. When the elbow is completely extended, the point of the elbow (olecranon) fits into a matching channel of the humerus, providing rigidity for the column of bones. Interestingly, this hinge type of action generally allows the lower limb to swing only in the direction it is pointed. (See Figure 4.)

dog Humerus
Figure 4. Elbow Joint: Figure 4A = Shaft(Body), Figure 4B = Olecranon of the Ulna (elbow), Figure 4C = Joint Capsule, Figure 4D = Ligaments

Determining the length of the humerus (upper arm) is vital when seeking the angulation of the scapula to the humerus. If the layback of the scapula is correct and the humerus is either too long or too short, the reach and the amount of leg lift (as well as the head carriage of the dog) can be affected. A dog with a short upper arm can lack forechest because the front assembly is placed too far forward, thus shortening the dog’s forward reach. There is a definite lack of support under the deepest part of the chest when the upper arm is short, and therefore, there is little “return” of the upper arm to position the elbow and the foreleg under the heaviest part of the chest. Legs placed too far forward put more stress on the muscles and bones of the forequarter. A short upper arm also hampers the ability of the leg to incline under the body toward the centerline of the dog when the dog is in motion.

A shortened upper arm can result in a dog that moves wide when coming toward you and rolls from side to side when seen from the side at a trot. This rolling or lateral movement (lateral displacement) in a moving dog wastes energy and wears the dog out. It may well eventually lead to a breakdown in the dog to the point it can no longer fulfill the job for which it was developed. Less often seen is a humerus that is too long, but this too causes changes in the prosternum and affects both the placement of the neck and the head carriage. “Too much” is as bad as “too little.” Anatomy is a fascinating science, and it always amazes me how every part of the dog must be in balance with the whole animal for everything to work flawlessly. We all know, however, that there is no perfection in nature and that every Best in Show dog has at least one fault. Our duty as breeders is to always strive for the “ideal” set forward by our breed standards. By doing this, we are doing all that we can to preserve our beloved breeds for future generations to love and be loved by these marvelous creatures we call dogs.

Please address any questions or comments to me via email: jimanie@welshcorgi.com.

 

Form Follows Function – Closer Look at the Humerus (Upper Arm) of a Dog
By Stephanie Seabrook Hedgepath

  • My involvement with the world of showing dogs began in 1969 with the purchase of my first show dog, a German Shepherd Dog. In the mid-seventies I began breeding and showing Pembroke Welsh Corgis under the Jimanie prefix and have finished a championship on a Pembroke Welsh Corgi on the average of one a year for the last 45+ years - almost all were breeder/owner handled to their titles. In 2010, I formed a loose partnership with two long-time friends, Denise Scott and Linda Stoddard, and we now breed and show under the Trifecta prefix. I am a breeder/owner/handler and still breed and show. Over the years I have owned and shown dogs mostly from the Herding and Sporting Groups plus a few toy breeds. I started out showing dogs from the Herding Group, but as a hunter, I always had a “bird dog” and thus also showed Brittanys, Pointers, Golden Retrievers and Irish Setters over the years. I have finished dogs in several other breeds from the Sporting and Toy groups. I started my judging career in 1988 with AKC approval to judge German Shepherds, Cardigan and Pembroke Welsh Corgis. I judge the Herding, Sporting and Toy groups and several of the Non-Sporting breeds, as well. I have been fortunate enough to have judged dogs all over the US and Canada and also in Finland, Norway, Sweden, Jamaica, New Zealand, Australia, Ireland, China, the Philippines, Mexico and the United Kingdom. In 2011, I was accorded the supreme honor of being asked to judge the Welsh Corgi League show in the UK and in previous years both the Cardigan and Pembroke Nationals in the US. I have also had the honor of having judged many National and Regional Specialties for breeds I did not breed, own or show from the sporting, herding and toy groups throughout the years, an assignment I always enjoy! Some of the highlights of my judging career have been judging at Westminster Kennel Club in 2006, doing the Herding Group at the Rose City Classic in Portland which was shown on Animal Planet and the national specialties for Clumber Spaniels, Field Spaniels, Australian Shepherds, Miniature American Shepherd, Bouviers (Canada) and the Top Twenty competition for the Golden Retriever Club of America as well as both of the Corgi national specialties in the US and Pembrokes in Canada and the Welsh Corgi League show mentioned above. I make my living as an artist, mostly through the design of counted cross-stitch and needlepoint but also through paintings and sculpture as well as jewelry. I have recently begun authoring and producing DVDs on the canine, mostly dealing with structure and movement. Last, but certainly not least, I’ve been married to Jim Hedgepath since 1972 and am the mother of two and the grandmother of four. Thank you for the honor of being invited to judge your dogs.

  • Show Comments

Your email address will not be published. Required fields are marked *

comment *

  • name *

  • email *

  • website *

You May Also Like

Dog Behavior | Temperament, Personality and Soundness

Dog Behavior | Temperament, Personality and Soundness

Dog Behavior | Temperament, Personality and Soundness: What is the one thing that is ...

Canine Spine

A Closer Look at the Canine Spine

The canine spine (vertebral column)  is not only the supporting structure of the body, ...

preservation breeder

Purebred or Preservation Breeder?

I am very pleased with the increasing usage of the term “preservation breeder,” which ...

style quality

Style and Quality

Style comes nearer than any other breed characteristic to “type,” and is of great ...