An Overview of Canine Anatomy – A Brief Guide to the Canine Body

Publishing Author : Jay Gray

Date Published : 18/10/18

 

Introduction

Understanding basic Canine Anatomy is paramount for all canine professionals.  Without this understanding, we cannot administer emergency first aid, or offer advice to those who need it before seeing a vet.  Although without appropriate qualifications, it is important to not offer medical advice in its true form, one can instruct others on basic issues and preventative measures around them.  For example, a dog with hip dysplasia or hip issues can be helped with physiotherapy but in order to do this, one must understand the hip joint and the mechanics involving this to properly understand the condition and rehabilitation.

Canine Anatomy, even at the most fundamental level can be very difficult to comprehend and is made much easier by starting with the biggest picture.  Learning the major bones and muscle groups first and then breaking down further into more detail as the understanding is increased.  The language used in Canine Anatomy can be overwhelming and difficult to understand even at the basic level, so it is important to break this down into smaller chunks, remembering a few terms per day over the course of learning.  Another helpful way to deal with these difficult (and often foreign based) words is to create mnemonics such as HSTMI (Hip, stifle, tarsus, metatarsus, interphalangeal.)  Creating a mnemonic around this can vastly improve the retention of the information.  An example of a mnemonic for this list would be ‘Henry Still Takes My Ink’.

 

Terms of Orientation and Direction

Terms of Orientation and direction are the beginnings of the fundamentals of canine anatomy.  Precision is the important factor when discussing things in the body, especially when this language relates to an injury, disease site etc.  The nine main directional terms are as follows:

Cranial: Towards the cranium or head of the body.

Caudal: Towards the cauda or tail end of the body or back of the head

Rostral: Within the head, towards the nose.

Dorsal: Towards the back surface; the surface away from the ground; also, the cranial aspect of the foot below the carpus and tarsus.

Ventral: Towards the belly; the surface closer to the ground.

Proximal: On a limb, a position that is more dorsal; also, a position nearest a point of muscle origin.

Distal: On a limb, a position that is more ventral; also, a position nearest the point of muscle insertion.

Palmar: (The same as the palm of the human hand).  Describes the caudal aspect of the forelimb below the carpus.

Plantar: (The sole of the human foot).  Describes the caudal aspect of the hind limb below the hock.

Ahead of these basic terms, there are a few more important terms relating to direction namely Lateral and Medial.  Lateral is a term relating to things away from the median plane or midline of the body whereas Medial is in relation to the inside position towards the median plane or midline of the body.

Using right and left within canine anatomy and fields relating to it is actually perfectly acceptable.  There is no need for a term more complicated than this but it is important to take the appropriate care needed to use them properly.  In the case of these terms, left and right must relate to the animal’s left and right, and not always the way the observer is viewing the animal.  If the animal is laid on it’s back, the terms are used as if from the first person of the animal.   Looking straight on to the observer, the left and right animal would be reversed compared to the left and right of the observer.  Confusion arises when this is not followed and understood properly and can result in serious implications, especially in veterinary medicine.

 

The Head

The domestic dog is the animal that shows the most variation (morphology) in its shape.  These variations become even more prevalent in the canine head of different breeds.  If we look at a Greyhound and a French Bulldog this difference becomes very obvious.

Skulls are generally labelled in one of three areas.  A brachycephalic skull is compressed or shortened (named after the brachycephalic artery).  Think of breeds such as Bulldogs, Pugs etc. The mesocephalic skull is of medium length and can be found in breeds such as the Collie, the Labrador etc and finally elongated skulls are known as dolichocephalic.  Both elongated, and standard-length skulls are unproblematic in health issues but short faced breeds (brachycephalic heads) can have fairly serious health issues.  The skull has been so reduced that breathing can be impaired, swallowing can be inhibited, teeth can become overcrowded, tear drainage can be reduced, and infections are profound due to the excessive folds in the skin.

A canine skull is made of sixteen bones and will be commonly listed in the following order (when written in conjunction with the Ventral View).  Incisive, Maxilla, Frontal, Occipital, Temporal, Zygomatic, Palatine, Preshphenoid, Pterygoid, Baisphenoid, Vomer, Upper Fourth Premolar, Parietal.

Alongside these sixteen bones, the canine skill also contains a vital joint which is used to allow the dog to open and close its mouth.  This joint is called the temporomandibular joint.  It is made up of the glenoid fossa, condylar process, tympanic bulla, ramus of mandible, angular process, articular process, articular eminence, zygomatic arch and the retroarticular process.

Dental Anatomy of the dog is found in the head and contains four types of tooth.  The incisors, canines, premolars and molars.  The three rooted teeth I the dog are all contained in the upper jaw.  Premolar 3, molar 1, and molar 2 are the only teeth with three roots within the canine skull.  The carnassial teeth are premolar 4 in the upper jaw, and molar 1 in the lower jaw.  These four types of teeth add up to the total of 42 teeth in total in the adult dog, and 28 teeth in total for the puppy.
Puppy – I 3/3   C 1/1   PM 3/3   M 0/0 – 28 Teeth total.
Adult dog – I 3/3   C 1/1   PM 4/4   M 2/3 – 42 Teeth total.

Because of the great variation in dog head shapes, the bite (also known as dental occlusion) is frequently distorted from normal.  It is important to be able to check for a normal bite when thinking about breeding or health testing a dog.  Normal occlusion has the following features:  Upper incisors should rest just rostral to the lower incisors. Lower canine should sit rostral to the upper canine and should be equally positioned in the space between the upper third incisor and the upper canine.  Upper and lower premolars should interdigitate like shears.  They should not rest directly on top of each other and finally the upper carnassial should sit lateral to the lower carnassial.  Malocclusion occurs when the lower jaw is longer than the upper jaw and is commonly referred to as an underbite.

The sixteen main bones found in the head are accompanied by twenty prominent muscles responsible for facial expression and mastication (chewing).  These muscles are (in order when in the lateral view).  Levator nasolabialis, orbicularis oculi,  levator muscle of medial eye, retractor muscle of lateral eye, frontalis, external ear muscles, intermediate sphincter muscle, platysma, parotidoauricularis,  zygomaticus, intermediate sphincter muscle, orbicularis oris, temporalis, masseter, digastricus, mandible, zygomatic arch, masseter, digastricus and the tongue.

 

The Axial Skeleton

The axial skeleton is the area of the dog running down the central axis of the body comprising of the skull, vertebral column, ribs, sternum and pelvis.  We have covered the main parts of the skull so this section of the paper will concentrate primarily on the spinal structure and the bones in relation to this.

If viewed from the lateral side, these are commonly listed as follows:

1 – Cervical Vertebrate, C1 – C7

2 – Thoracic Vertebrate, T1 – T13

3 – Lumbar Vertebrate, L1 – L7

4 – Sacrum, S1 – S3 (Fused)

5 – Caudal Vertebrate

6 – Thoracic Inlet

7 – Costal Arch

8 – Intercostal Space

9 – Interchondral Space

10 – Manubrium of sternum

11 – Sternebrae

12 – Xiphoid Cartilage

Most companion dogs will tend to have 10-20 caudal vertebrate providing that they have not been docked, but this can vary from breed to breed hence the large average provided.

 

Forelimb Muscular-Skeletal Model

The forelimb is commonly known as the thoracic limb because it attached to the thorax by muscles.  Understanding the forelimb is paramount again for people wanting to breed their dogs or looking to compete in any physical sports because the thoracic limb is prone to a few issues.  The elbow joint is commonly affected by arthritis in older dogs and younger dogs can also experience panosteitis type symptoms around the elbow joint as well.  Certain breeds are also prone to elbow dysplasia, a condition in which multiple issues with the ball and socket joint are apparent.

The elbow joint itself is compiled of 9 major parts.  These are, the shaft of the humerus, olecranon of the ulna, joint capsule, medial collateral ligament, cranial and caudal parts of the medial collateral ligament, annular ligament, lateral collateral ligament, cranial and caudal parts of the lateral collateral ligament and the oblique ligament. This is the joint in its entirety and it falls on the ventral side of the shoulder and brachium itself.  The shoulder and brachium (or arm) are made up of nine main parts and they are as follows.
Sternocephalicus
Cleidocervicalis part of the brachiocepalicus
Omotransversarius
Trapezius
Deltoideus
Latissimus dorsi
Triceps brachii, long and lateral heads
Deep pectoral

 

Summary of Forelimb Muscle Functions

It is important to remember that within the canine’s anatomy, almost all muscles tend to work in groups so learning about the isolated actions and functions of said muscles is not always realistic.  Some muscles, especially broader, flatter muscles can have different actions on the limb and joints, depending on what other muscles are engaged at the same time, or how the limb is positioned

Below is a table explaining the extrinsic muscles of the forelimb.

Muscle Name Description and Course Function Nerve Supply
Trapezius Triangular muscle, running from the supraspinious ligament in the cervical and thoracic regions to the spine of the scapule Raises and advances the forelimb Accessory Nerve
Omotransversarius Narrow, band like muscle running from the atlas to the acromion of the scapula. Advances the forelimb. Accessory Nerve
Brachiocephalicus Complex muscle running from the various points on the head and neck to the humerus.  Different parts of this are separately named. Advances the free limb. When the limb is weight bearing, it moves the head and neck down, or to either side. Accessory Nerve.
Latissimus Dorsi Very broad muscle running from wide areas across the thoracolumbar region to the teres tuberosity of the humerus. Holds the scapula against the trunk and retracts the free limb.  When the limb is weight bearing, this muscle helps propel the body forwards against the planted limb. Thoracodorsal Nerve.
Rhomboideius Triangular muscle with a wide base that lays under the trapezius and runs from the midline of the neck to the dorsal and medial surface of the scapula. Raises and retracts the forelimb. Brachial Plexus Nerves.
Superficial Pectoral Two-part muscle running from the sternum to near the deltoid tuberosity of the humerus area. Moves the limb towards the body (known as adduction) Brachial Plexus Nerves

 

Deep Pectoral Muscle runs frm the ventral sternum to the lesser tubercle of the humerus. Together with the serratus ventralis, acts as a sling to support the trunk between the forelimbs.  It retracts the free forelimb and advances the body against the planted forelimb. Brachial Plexus Nerves.
Serratus Ventralis Large, fan shaped muscles running from the cervical vertebrae and ribs to insert dorsally on the medial side of the scapula. Supports the weight of the trunk between the shoulders and can also advance or retract the limb depending on the limb position.  The muscle is also responsible for movement in the neck. Brachial Plexus Nerve Branch.

 

The extrinsic muscles listed above connect the limbs to the body, and act as a sling to suspend the body between the forelimbs.  Their role in locomotion depends on position of the leg, whether the leg is weight-bearing or not, what other muscles are doing, what portion of big muscles are being used etc.  The intrinsic muscle groups (not listed in this paper but can be found in completion in ‘The Dog Anatomy Workbook P.73. P.75, P.77’) move the limb in multiple ways to allow movement.  Flexion, extension, rotation, abduction, adduction etc. 

The Hip Structure

The hip joint is a ball and socket joint found at the caudal end of the pelvis attaching the leg to the pelvis.  In the normal hip, the head of the femur is kept in the acetabulum by the round ligament, the fibrous joint capsule, the heavy surrounding muscles and the suction effect of the femoral head in the cup of the acetabulum.  The round ligament inserts on a small depression in the centre of the head of the femur, called the fovea.

Understanding the hip joint (much like the elbow joint) is important because of the fairly common condition known as hip dysplasia.  In this condition, the acetabulum socket is poorly shaped and flatter than it should be.  This, combined with other changes in the joint, causes joint instability, arthritis and pain.

Hip dislocation occurs generally after a trauma and he femoral head is knocked out of the acetabulum, tearing the joint capsule and rupturing the round ligament.  The conformation of the hip joint means that dislocation usually occurs in a cranial and dorsal direction.

Below is a complete list of the hip bones.

1 – Ilium

2 – Ischium

3 – Pubis

4 – Dorsal Iliac Spine

5 – Ventral Iliac Spine

6 – Ischiatic Spine

7 – Obturator Foramen

8 – Ischiatic Tuberosity

9 – Pelvic Symphysis

10 – Ischiatic Arch

11 – Iliopubic Eminence

12 – Articular Surface for the Sacrum

13 – Sacrotuberous Ligament

14 – Acetabulum

15 – Sacrum

16 – Caudal Vertebra 1

Alongside the issues in the hip such as Hip Dysplasia and Hip Dislocation there are also issues involving the rear lower leg, specifically the common calcaneal tendon.  The common calcaneal tendon brings about extension of the hock joint.  The tendon inserts on the calcaneius.  Weakening, rupture or detachment (avulsion) of the tendon from the calcaneius results in unopposed hock flexion.  If this happened, the dog would have a plantigrade stance, with the metatarsals placed flat on the floor.  If the common calcaneal tendon is only partly ruptured, with the tendon of the superficial digital flexor remaining intact, the dog adopts a characteristic ‘crab like’ stance because of the flexion of the toes.  Partial rupture or degeneration of the tendon is especially common in the Doberman Pinscher.

 

 

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