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Lymph nodes, where the lymph is filtered, play a crucial part in the body’s immune system. Harmful substances which are not neutralized in one node can be carried to the next successive node, where the lymph will again be filtered. Lymphocyte activity in the nodes increases when an infection is present; hence, the lymph nodes become swollen and painful. Phagocytic leucocytes remain in the lymph nodes, destroying harmful substances in situ. Also, antibodies produced by different lymphocytes are released into the lymph and circulate in the lymph and the bloodstream.

As in the venous system, the lymphatic system does not have an intrinsic pump and, in similar fashion to the venous system, relies on secondary mechanisms to elicit effective drainage. Again, the skeletal muscles play a large role in effecting this. Like the venous system, the lymphatic system contains small semilunar values to prevent back flow. Also, the adjacent arteries and veins assist with the distal to proximal flow. As with blood flow, pressure changes within the thoracic cavity are important for continuing lymphatic movement. Therefore, when a dog is active and there is good skeletal muscular movement, the system can work efficiently, aiding adequate detoxification.

Massage can influence the lymphatic system effectively, especially in the veteran dog, or one with impaired mobility. This could be used to great effect postoperatively, when movement is restricted; also, the effective removal of postanaesthetic toxins could aid a fast recovery. In some cases of lymphoedema, appropriate massage can ease the symptoms by assisting drainage, using gentle massage over the most proximal lymphatic node to where the swelling is at its most exaggerated, and then applying light and gentle effleurage (a form of massage), working proximally from the isolated lymph node.

In conclusion, the lymphatic system plays a very important role in the body’s defence system. Working alongside the venous system it forms a vital cleaning system for the body, without which homeostasis would not be possible and other systems, such as the musculature, would be compromised.

Comparative human and canine anatomy

Comparative anatomy of the human and dog is an in-depth and precise science; however, for the purpose of this chapter, it has been simplified into areas that are relevant to our area of study. Although studying the differences between the human and the dog is not essential, it is widely accepted by many practitioners as being extremely interesting and helpful. In fact, studying and treating humans can provide a greater insight into applying physical therapy and understanding physiology and anatomy. A human can provide verbal feedback and can be requested to lie still; also, so much more is visible when the skin is not covered in fur. By looking at both the human and dog, one can learn the many similarities between the two species and how they differ. For example, skeletally, all mammals look quite similar. However, a dog can jump proportionally much higher than a horse; to understand how this is possible, and how a dog moves, can give a practitioner a greater knowledge in order to provide effective treatment.

The easiest way to visualize the differences between a canine and a human skeleton is to ‘crush’ the human ribs to form an angulated sternum and then place the scapulae adjacent and opposite on the sagittal plane (47). The obvious difference between the two is that a human has a plantigrade stance (we take the body’s weight on the plantar surface of our feet), whereas a dog’s stance is digitigrade, meaning they bear weight on their

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	Scapula or	Clavicle
	shoulder
		or collar	Scapula or
	blade
		bone	shoulder
	Pelvis		blade
	Femur
	Knee/stifle		Pelvis
			Femur
			Knee/stifle

Hock/ankle

Hock/

ankle

47 Comparison between dog (digitigrade) and human (plantigrade) skeletons.

phalanges or digits. Due to the dog being a quadruped and the human a biped, weight transference and mobility is reflected within the foundation and supporting structures of the body. Most joints allow movement through more

than one plane; however, the dog’s most obvious limitations are through the joints providing movement through the dorsal and ventral planes (adduction and abduction), and some rotational movements through the transverse plane.

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Appendicular skeleton

Thoracic limb

Scapula

The scapula in the dog supports the main muscles used for support, mobility, and weightbearing while in motion and when static. It also receives and dissipates concussion. The potential movement of the scapula can be defined by its orientation and angulation with the thoracic cage. The spines of the scapulae lie at an angle of approximately 35° on the transverse plane, which naturally differs according to breed or type, and therefore intended use. Its attachment to the axial skeletal is solely by soft tissue and its design and role constitutes a major difference between the two species.

The human scapular spine lies on the same relative transverse plane, at 45°; however, due to the free movement required of the arm in the transverse lateral/medial plane, extra stability is required which is facilitated by the clavicle. The dog does not possess a clavicle in the form that a human does and instead, for shoulder stability and strength, it possesses a truncated clavicle in the form of an oval cartilaginous structure that does not articulate with the rest of the skeleton. It spans approximately 1 cm and is located at the tendinous intersection of the brachiocephalicus muscle, in approximately the same anatomical position as the human clavicle.

Humerus

In relation to its human counterpart, the dog has an altered thoracic limb structure to manage its weight and any concussion properties required. The proximal humerus has a more flattened head than that of the human, and distally has a welldefined olecranon fossa and supratrochlear foramen for securing the anconeal process of the ulna; this is crucial for shoulder

stability. This is a problematic area for many breeds, as this is a contributory factor in elbow dysplasia; the humerus in the achondroplastic breeds is often bowed to facilitate the shoulder assembly.

There are basically three types of front assemblies in the dog, and these can be used to define the use of a dog. The achondroplastic type are short-legged dogs such as a Dachshund or some Jack Russell terriers; these have shortened limbs, often with valgus or varus lower limb (bowed through carpal growth discrepancy) but have a good angulation between scapula and humerus required for digging. Greyhounds and Lurchers have a less pronounced shoulder angulation than the achondroplastic dog, lending itself to speed. The third type is the dog intended for retrieving or herding work, where the most distal part of the humerus should align with the most caudal aspect of the dorsal scapula region. This angulation is intended for good muscle attachment to provide balance and strength.

Ulna

The ulna in most breeds is the longest bone in the dog. It possesses a large and prominent olecranon process, forming the point of the elbow. This is designed to hold the powerful and supporting triceps brachii muscle group, which are stabilizing and anti-gravitational.

Carpal joints

The carpal joints in the human and canine contain the same number of bones, but in the canine, two are fused and they have a slightly differing construction. In the human, the retinaculum across the palmar side of the wrist draws the outer bones of the wrist together, thus forming a welldefined ‘tunnel’; this forms a housing for the tendons and median nerve (when the median nerve is compromised, carpal tunnel syndrome ensues). The dog possesses the same number of carpal

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bones but the arrangement is altered, with the radial carpal bone parallel to the fused scaphoid and lunate bones.

Axial skeleton

Vertebral column

The vertebral formula is different in the human and the dog:

Canine: C7, T13, L7, S3 (fused), caudal (CA) or coccyx 15–21.

Human: C7, T12, L5, S5 (fused), coccyx 3–4.

Costals

The costals are small bones that articulate with the thoracic vertebrae in both the dog and the human, providing protection for the heart and lungs within the thoracic chamber. In the dog (to a greater extent than in the human), they also help support the shoulder assembly through extrinsic muscular connections; in the dog, this provides stability and fluidity through costal movement when it is in motion.

Pelvis

The fused ilium, ischium, and pubis bones comprise the pelvis, with the ischium providing a wide and broad projection caudally to support the massive hamstring muscle group that is required for propulsion and elevation. The pelvis of the dog is a different shape to that of the human; it is smaller and narrower, and lies within the transverse and dorsal planes.

The commonality between the species is that they both possess a muscular system to suit their function. This means that they both have deep supporting muscles that ensure the stability of the axial skeleton, which enables the appendicular skeleton to be appropriately supported and stabilized too. This can also ensure that the joints become efficient and economical levers, providing sustained movement to the whole.

Pelvic limbs

The femur is the heaviest and largest bone in the dog, whereas the ulna is the longest; in the human, the longest bone is the femur. The stifle is constructed in the same configuration as in the human knee, both relying on good conformation for stability. Muscular stability is provided through the pelvis, plus tendons and ligaments that provide integrity to the joint. The calcaneous of the dog is almost identical to the human ankle (calcaneous) bone, both supporting the Achilles tendon. The canine tarsus contains the same number of bones as the human’s, being similar to the human ankle. However, as with the palmar surface of the thoracic limb, the plantar surface of the pelvic limb is the phalanges.