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How many ribs does a dog have and how does this relate to the number of thoracic vertebrae present?
13 ribs and 13 thoracic vertebrae
How many ribs/thoracic vertebrae does a horse, cow and cat have?
- Horse - 18 and 18
- Cow - 13 and 13
- Cat - 13 and 13
Why is the distal end of each rib cartilage and not bone?
To allow flexibility at the articulations between the ribs and thoracic vertebrae so the ribcage can expand and contract during respiration
Which structure attaches around the costal arch?
How many intercostal spaces are there in the dog? What occupies these spaces in life?
12. They are occupied by intercostal muscles.
What important structures pass through the thoracic inlet in life?
Oesophagus, trachea, major blood vessels
What are the functions of the thoracic wall?
- Provides protection for the vital organs and structures located within
- Plays a role in breathing/respiration
- Ribcage provides large surface area for muscle attachment
Does every pair of ribs have an intercapital ligament?
No, only ribs 1-10
Which other ligament is closely related to the intercapital ligament?
Dorsal longitudinal ligament of the vertebral column
Which vertebrae does rib 5 articulate with?
T4 and T5
Which vertebrae does rib 11 articulate with?
What is the function of the latissimus dorsi muscle and where does it get its nerve supply?
- Function - forelimb retractor, shoulder flexor
- Innervation - brachial plexus
What is the main function of the pectoral muscles and where do they get their nerve supply?
- Function - forelimb adductors
- Innervation - brachial plexus
What is the function of the EAO muscle in relation to the thorax? By looking at an animal how would you be able to tell that the external abdominal muscle was functioning this way?
- Function = assists with expiration. Active contraction of the EAO muscle assists with expiration and the presence of intercostal muscles ensures that the whole ribcage moves together in a caudal direction to compress the thoracic cavity and produce an increased expiratory effort.
- An animal would have increased abdominal effort or 'heaving flanks'
What is the function of the serratus ventralis muscle in relation to the thorax? By looking at an animal how would you be able to tell that the serratus ventralis muscle was functioning in this way?
- Function = major accessory inspiration muscle. If the forelimbs are fixed in position then the attachment of the SV muscle along the ribcage functions to pull the ribs cranially and laterally.
- Animals with increased respiratory rate will stand with their elbows slightly abducted to allow the SV to function in this way
What other function does the SV fulfil?
- It suspends the weight of the animal's thorax between the forelimbs
- Forelimb protractor and retractor
- Lateral flexion of neck region
- Part of stay apparatus in the horse
What is the function of the intercostal muscles?
They ensure the ribs move together (by linking the movement of each rib to its neighbour) during inspiration and expiration and therefore function as a single unit
What are the main functions of the abdominal wall
- Protection and support to vital organs and structures within
- Abdominal press
- Plays a role in breathing/respiration
How would you describe the fibre direction of each of the abdominal wall muscles?
- EAO - caudoventral
- IAO - cranioventral
- TA - ventrodorsal
- RA - craniocaudal
What structures form the inguinal canal and where are they located?
- Superficial inguinal ring - caudoventral region of EAO muscle
- Deep inguinal ring - opening at caudoventral region of IAO muscle
How does the sex of the animal influence what structures run through this opening?
- Male - spermatic chord, testes, cremaster muscle
- Female - vaginal process
- Both - external pudendal artery and vein, genitofemoral nerve
What are the cranial and caudal attachments of the linea alba?
- Cranial - sternum (xiphoid)
- Caudal - pubic bone
What are the layers that you would incise down through when making a surgical incision through the lateral aspect of the thoracic wall?
Skin, cutaneous trunci muscle, superficial fascia, deep fascia and muscle, intercostal muscles, pleura
Where in relation to the ribs would you make your incision and why?
In the middle of the intercostal space as the intercostal vein, artery and nerve run down the caudal aspect of the rib to the level of the costochondral junction where they branch to run down both sides of the rib
What are the layers that you would incise down through when making a surgical incision through the ventral aspect of the abdominal wall? Which species would you routinely employ this approach with?
- Skin, superficial fascia, tunica flava, linea alba, peritoneum
- Small animals and horses
What are the layers that you would incise down through when making a surgical incision through the lateral aspect of the abdominal wall? Which species would you employ this approach with?
- Skin, superficial fasica, tunica flava abdominus (cow), EAO, IAO, TA, peritoneum
- Cows and cats
Cartilage should not be well visualised on radiographs yet some of the costal cartilages are visible on this radiograph - why do you think this is the case? Is this normal in dogs?
Mineralisation of the costal cartilage as dogs age and therefore they become visible on radiographs - this is a normal finding
What structures form the thoracic inlet?
T1, 1st pair of ribs, manubrium
Which ribs contribute to the costal arch in the dog? Where do the other ribs attach?
- R1-9 articulate with the intersternebral cartilages
- R13 does not articulate with anything - 'floating rib'
How is the mediastinum formed?
The endothoracic fascia and parietal pleura on each side meet to form a midline partition - the mediastinum
What structure would normally occupy the mediastinal recess?
The accessory lobe of the right lung
What structures are found within the plica vena cava?
The caudal vena cava and right phrenic nerve
What is the functional relevance of pleural recesses?
Allow expansion of the lungs into the apex, base and ventral borders during inspiration
Name the serous membrane that covers the cranial/caudal surfaces of the diaphragm
- Cranial - diaphragmatic pleura
- Caudal - periotoneum
Explain where the aortic hiatus is located in relation to lumbar attachments of the diaphragm and to the oesophageal hiatus and caval foramen
It is located between the left and right crura. It is cranial to the oesophageal hiatus and caval foramen
List the structures that pass through the different openings of the diaphragm
- Aortic hiatus - aorta, azygous vein and thoracic duct
- Oesophageal hiatus - oesophagus and vagus nerve
- Caval foramen - caudal vena cava
What is the clinical significance of the costodiaphragmatic line of pleural reflection?
It marks the boundary between pleural and peritoneal cavities. Entrance to the pleural cavity is crania-dorsal to the line e.g. to draw off for pleural effusion. Entrance to the peritoneal cavity is caudo-ventral to the line.
Which major organ do the left and right phrenic nerves innervate?