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There are eight pairs of cervical spinal nerves in the dog. The first cervical spinal nerve passes through the lateral vertebral foramen of the atlas. The re-maining nerves pass through succeeding interver-tebral foramina. The eighth cervical spinal nerve emerges from the intervertebral foramen between the seventh cervical and first thoracic vertebrae.

Immediately on leaving the foramina, the nerves divide into large ventral and small dorsal branches.

The dorsal branches supply structures dorsal to the vertebrae (Fig. 3-6) and will not be dissected. When nerves are being dissected, it is helpful to separate the tissue bluntly by inserting a scissors and open-ing it to spread the tissue. Fascial strands of connec-tive tissue will break, but nerves usually stretch.

Rhomboideus capitis

Trapezius

Supraspinatus

To phrenic nerve

Cleidocephalicus pars mastoideus

Cleidocephalicus pars mastoideus

Cleidocephalicus pars cervicalis

Cleidocephalicus pars cervicalis

Cleidobrachialis

Clavicular intersection Omotransversarius

Vagosympathetic trunk Common carotid artery

Sternocephalicus Splenius

Serratus ventralis

XI C2

C3 C4

C5

Fig. 3-1  Ventral branches of cervical spinal nerves emerging through the lateral musculature.

CHAPTER 3 The Neck, Thorax, and Thoracic Limb 95

Palpate the wing of the atlas and dissect the fascia near its caudoventral border to uncover the ventral branch of the second cervical spinal nerve (Figs.

3-1 and 3-2). This lies along or deep to the middle of the caudoventral border of the platysma, which is dorsal to the external jugular vein. Separate the overlying fascia until the nerve is found. It emerges between the mastoid part of the cleidocephalicus (cleidomastoideus) and the omotransversarius. The ventral branch of the second cervical spinal nerve di-vides into two cutaneous branches: (1) The great au-ricular nerve (Figs. 3-2, 3-3, 5-39) extends toward the ear. It branches and supplies the skin of the neck, the ear, and the back of the head with sensory branches.

Trace the nerve as far as present muscle and skin re-flections will allow. (2) The transverse cervical nerve (Figs. 3-2, 3-3) branches to the skin of the cranioven-tral part of the neck and need not be dissected.

The external jugular vein (Figs. 3-2, 3-3), on the side of the neck, is formed by the linguofacial and maxillary veins (Figs. 3-15, 5-39, 5-40). The ovoid body that lies in the fork formed by these veins is the mandibular salivary gland (Fig. 3-2). The mandibular lymph nodes (Figs. 2-12, 3-2) lie on both sides of the linguofacial vein, ventral to the mandibular salivary gland.

Ligate and transect the external jugular vein at its approximate middle and reflect each end.

Sternocephalicus:

pars occipitalis Caudal auricular nerve (VII)

Accessory nerve Omotransversarius

Platysma Trapezius

Parotid gland Parotid duct

Ventral buccal branch (VII)

Cervical br. of VII Mandibular gland

Br. to cleidocephalicus pars mastoideus and sternocephalicus

C2, ventral branch Great auricular nerve Transverse cervical nerve Parotidoauricularis

C3, ventral branch

External jugular vein Sternocephalicus C4, ventral branch

C5, ventral branch

Cleidocephalicus pars mastoideus Cleidocephalicus pars cervicalis

Fig. 3-2  Superficial nerves of the neck, lateral aspect.

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96

In some specimens the omobrachial and ce-phalic veins (Figs. 3-3, 3-35) may be observed entering the external jugular vein after crossing the shoulder. These may be transected and re-flected. Free the sternocephalicus and transect it 3 cm from its origin. Reflect it craniodorsally to a point cranial to the place where the second cervical nerve crosses the muscle. Transect the cleidocephalicus 1 cm cranial to the clavicular intersection. Reflect it toward its cervical and mastoid attachments.

The superficial cervical lymph nodes (Fig. 3-26) lie in the areolar tissue cranial to the shoulder.

They lie deep to the cervical part of the cleidoce-phalicus and the omotransversarius and receive lymph drainage from the cutaneous area of the head, neck, and thoracic limb.

The accessory or eleventh cranial nerve (Figs. 3-1, 3-3, 5-52) is a large nerve found deep to the cranial part of the sternocephalicus and the cervical part of cleidocephalicus. As it emerges from the neck, it crosses the second cervical spinal nerve, runs along the dorsal border of the omotransversarius, and ter-minates in the thoracic part of the trapezius. Dissect between the trapezius and cleidocephalicus and identify this nerve coursing caudally to the trape-zius. The accessory nerve is the only motor nerve to the trapezius. In addition, it supplies in part the omo-transversarius, the mastoid and cervical portions of the cleidocephalicus, and the sternocephalicus.

Free the ventral border of the omotransversarius and lift it. Look for the ventral branches of the third, fourth, and fifth cervical spinal nerves (Fig. 3-1), which are distributed in a segmental manner to the

Great auricular nerve (2nd cerv.) Accessory nerve

Superficial cervical artery and vein Cervical nerve medial

cutaneous branch Deep cervical artery and vein

cutaneous branches

2nd thoracic nerve lateral cutaneous branch

Subscapular vein and artery, cutaneous branches

Caudal circumflex humeral artery and vein

Intercostobrachial nerve

Triceps muscle (lateral head)

3rd intercostal nerve, ventral cutaneous branch

Internal thoracic vein and artery, perforating branch

Caudal cutananteous

antebrachial nerve (ulnar) Median cubital vein

Superficial brachial artery and vein

Radial nerve, superficial branch Cephalic vein

Cranial lateral cutaneous brachial nerve (axillary)

Cleidobrachialis muscle Cephalic vein

Axillobrachial vein Omobrachial vein

External jugular vein Transverse cervical nerve

Fig. 3-3  Superficial structures of scapula and brachium, lateral view.

CHAPTER 3 The Neck, Thorax, and Thoracic Limb 97

muscles and skin of the neck. The third and fourth nerves, after emerging from the intervertebral fo-ramina, pass through the deep fascia and the omo-transversarius. It may be difficult to identify each cervical nerve, and it is not necessary to do so.

Transect the fused sternohyoideus and sterno-thyroideus 2 cm from their origin and reflect them to their insertions. Parts of the trachea, larynx, thy-roid gland, esophagus, and carotid sheath are ex-posed. Identify these structures on your specimen.

Note the common carotid artery dorsal to the ster-nothyroideus. Bound to its medial side is the va-gosympathetic nerve trunk. The medial retropha-ryngeal lymph node (Figs. 2-12, 5-42) lies opposite the larynx, ventrolateral to the carotid sheath.

THORAX

Superficial Vessels and Nerves of the Thoracic Wall

Before dissecting the thoracic nerves and vessels, study Figs. 3-4 through 3-7, which show the pat-tern of distribution of these structures. Notice that

Internal intercostal muscle Transversus thoracis

muscle

Ventral intercostal branch Internal thoracic artery

Perforating branch

Dorsal intercostal artery Aorta Dorsal branch

Spinal branch Lateral cutaneous

branch Lateral cutaneous

branch

External intercostal muscle

Fig. 3-4  Schematic transection of thoracic wall to show  distribution of an intercostal artery.

External intercostal

Perforating branch Internal thoracic artery Ventral intercostal branches

Dorsal intercostal artery Internal intercostal

Internal intercostal

Lateral cutaneous branch

Lateral cutaneous branch

Aorta

Dorsal branch 7th thoracic vertebra

Fig. 3-5  Intercostal arteries as seen within rib cage.

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98

the artery and nerve of each intercostal space di-vide into dorsal and ventral branches. The dorsal branches enter the epaxial muscles. The ventral branches descend in the intercostal spaces along the caudal border of each rib. The dorsal and ven-tral arterial branches are derived from the dorsal intercostal arteries (Figs. 3-4, 3-5). The first three dorsal intercostal arteries come from a branch of the costocervical trunk; the remaining nine come from the aorta. The dorsal intercostal arteries and veins have lateral cutaneous branches that perforate the intercostal and adjacent muscles to supply cutaneous structures, including the tho-racic mammary glands. The dorsal intercostal artery and vein pass ventrally, where they anas-tomose with ventral intercostal branches from the internal thoracic artery and vein. At the ven-tral aspect of each intercostal space, perforating branches of the internal thoracic vessels emerge and supply cutaneous structures and the thoracic mammary glands. The dorsal and ventral nerve branches are derived from the spinal nerve as it emerges from the intervertebral foramen (Fig. 3-6).

Medial branch Thoracic nerve

Dorsal branch Lateral branch

Ventral branch Lateral

cutaneous branch

Lateral cutaneous branch

Intercostal nerve

External

intercostal Internal intercostal

Transversus thoracis

Ventral cutaneous branch

Spinal cord

Ramus communicans to sympathetic trunk

Fig. 3-6  Schema of a thoracic spinal nerve.

Thoracic nerve, cutaneous branch and intercostal artery and vein,

lateral cutaneous branches Cutaneus trunci

Subscapular artery and vein, cutaneous branches

Intercostobrachial nerve, 2nd intercostal nerve, lateral cutaneous branch

Lateral thoracic artery, vein and nerve Perforating branches of internal thoracic

artery, vein and intercostal nerve, ventral cutaneous branch Intercostal nerve,

lateral cutaneous branch Superficial cranial

epigastric artery and vein

Fig. 3-7  Superficial vessels and nerves of thorax, right lateral view.

CHAPTER 3 The Neck, Thorax, and Thoracic Limb 99

The ventral branches of the first 12 thoracic spinal nerves are intercostal nerves and have lateral and ventral cutaneous branches and branches medial to these that go largely to muscles.

Dorsal and lateral rows of lateral cutaneous branches of intercostal nerves, arteries, and veins emerge at regular intervals between the ribs and supply the cutaneous muscle, subcutaneous tis-sue, and skin (Fig. 3-6). The nerves of the dorsal row arise from the dorsal branches of the thoracic spinal nerves. A row of ventral cutaneous branches emerge through the origin of the deep pectoral muscle after having penetrated the ventral ends of the intercostal spaces. These vessels are perfo-rating branches of the internal thoracic artery and vein. The nerves are terminal branches of the in-tercostal nerves. Although these emerge at regular intervals, not all will be seen in the dissection.

The cranial thoracic mamma is supplied by the fourth, fifth, and sixth ventral and lateral cuta-neous vessels and nerves and by branches of the lateral thoracic vessels. The latter are from the axil-lary vessels, which will be dissected later.

The caudal thoracic mamma is supplied in a similar manner from the sixth and seventh cutaneous nerves and vessels. In addition, mam-mary branches of the cranial superficial epigastric vessels supply this mamma.

The axilla is the space between the thoracic limb and the thoracic wall. It is bounded ventrally by the pectoral muscles and dorsally by the attach-ment of the serratus ventralis to the scapula. Crani-ally, it extends under the muscles that extend from the arm to the neck. Caudally, a similar extension is found under the latissimus dorsi and cutaneus trunci.

The lateral thoracic artery, vein, and nerve emerge from the axilla between the latissimus dorsi and deep pectoral muscles. The nerve is mo-tor to the cutaneus trunci and may be found on its ventral border. It consists of fibers from the ventral branches of the eighth cervical and first thoracic spinal nerves. The vessels are branches of the axil-lary artery and vein that supply the muscle, skin, and subcutaneous tissues, including the cranial thoracic mamma. If these vessels and this nerve are not readily identified in your dissection, you may find them later when the axillary vessels and the brachial plexus are dissected.

Transect the pectoral muscles close to the ster-num. Reflect them toward the forelimb to expose the axilla.

The axillary lymph node lies dorsal to the deep pectoral muscle and caudal to the large axillary vein coming from the arm. Most of the afferent lymph vessels of the thoracic wall and deep struc-tures of the limb drain into this node.

LIVE DOG

Palpate the structures in the neck ventral to the cervical vertebrae. The larynx and trachea are readily palpable. The esophagus is usually too soft to feel but should be on the left of the trachea in the middle and caudal cervical region. Try to pal-pate a pulse in the carotid artery. It usually courses along the dorsolateral side of the trachea but is too deep to allow a pulse to be felt regularly. Cranially, feel the firm oval mandibular salivary gland and the smaller, looser mandibular lymph nodes. The latter can be felt subcutaneously at the angle of the mandible. Caudally in the neck, feel the superficial cervical lymph nodes cranial to the shoulder and deep to the omotransversarius or cleidocephalicus muscle. Extend the neck and compress the vessels that enter the thorax at the thoracic inlet to try to distend the external jugular vein so that it is visi-ble. This is more difficult to observe in long-haired breeds without removing the hair.

Deep Vessels and Nerves of the Thoracic Wall

Expose the lumbar and costal origins of the exter-nal abdomiexter-nal oblique and detach them. Reflect the muscle ventrally to the rectus abdominis. Re-flect the mammae if necessary. Free the aponeurotic thoracic attachment of the rectus abdominis close to the sternum and first costal cartilage. Reflect the rectus abdominis caudally, noting and cutting any nerves or vessels that enter the deep face of the muscle from any of the intercostal spaces.

The cranial epigastric artery is a terminal branch of the internal thoracic artery that emerges from the thorax in the angle between the costal arch and the sternum. It passes caudally on the deep surface of the rectus abdominis. The cra-nial epigastric artery gives rise to the cracra-nial su-perficial epigastric (Figs. 3-7, 4-2, 4-32), which perforates the muscle and runs caudally on its ex-ternal surface. This artery supplies the skin over the rectus abdominis and the caudal thoracic and cranial abdominal mammae. The cranial epigas-tric vessels continue on the deep surface of the rectus abdominis. Most of their branches termi-nate in this muscle.

Guide to the Dissection of the Dog

100

Make a sagittal incision completely through the thoracic wall 1 cm from the ventral median plane on each side. These incisions should extend from the thoracic inlet through the ninth costal carti-lage. The transversus thoracis muscle is a flat, fleshy muscle on the medial surface of the costal cartilages of ribs 2 though 8 (Figs. 3-4, 3-6). Its fas-cicles extend from the costochondral junctions to the sternum. Connect the caudal ends of the right and left sagittal incisions and free the sternum, ex-cept for the wide, thin fold of mediastinum that is now its only attachment.

On the right half of the thorax, clean and tran-sect the origin of the latissimus dorsi and reflect it toward the forelimb. Locate and transect the cau-dal portion of the origin of the serratus ventralis, exposing the ribs. Starting at the costal arch and using bone cutters, cut only the ribs, close to their vertebral articulation within the thorax, without damaging the sympathetic trunk. Reflect the tho-racic wall without removing it. As this is done, cut the attachments of the internal abdominal oblique, transversus abdominis, and diaphragm from the ribs along the costal arch. If this is done carefully, the peritoneal cavity will not be opened. Reflect the left thoracic wall in a similar manner.

On the internal surface of the thoracic wall, no-tice the intercostal vessels and nerves coursing

along the caudal border of the ribs. Ventrally, the vessels bifurcate and anastomose with the ventral intercostal branches of the internal thoracic artery and vein. The intercostal nerves supply the inter-costal musculature. Their sensory branches were seen as lateral and ventral cutaneous branches.

The pleurae (Figs. 3-8, 3-9) are serous mem-branes that cover the lungs and line the walls of the thorax. These form right and left sacs that en-close the pleural cavities. Each consists of visceral and parietal parts, depending on their location.

The pulmonary or visceral pleura closely at-taches to the surfaces of the lungs, following all their small irregularities as well as the fissures that separate the two lobes.

The parietal pleura is attached to the thoracic wall by the endothoracic fascia. This pleura may be divided into costal, diaphragmatic, and medi-astinal parts. Each of these is named after the re-gion or surface it covers, and all are continuous, one with another. The costal pleura covers the inner surfaces of the ribs and their associated in-tercostal and transversus thoracis muscles. The diaphragmatic pleura covers the cranial surface of the diaphragm. The mediastinal pleurae are the layers that cover the sides of the partition between the two pleural cavities. The mediastinum in-cludes the two mediastinal pleurae and the space

Brachiocephalic trunk

Pleural cavity

Thymus

3rd sternebra 2nd thoracic vertebra

A

Esophagus

Left subclavian artery

Cranial mediastinum

Parietal mediastinal pleura Pulmonary pleura

Right lung, cranial lobe Cranial vena cava Trachea

Longus colli muscle

Parietal costal pleura

Fig. 3-8 A, Schematic transverse section of thorax through cranial mediastinum, caudal view.

CHAPTER 3 The Neck, Thorax, and Thoracic Limb 101

1.   Longus colli muscle 2.   Trachea

3.   Cranial vena cava 4.   Right cranial lobe

5.   Cranial mediastinum

6.   Cranial part of left cranial lobe 7.   Brachiocephalic trunk 8.   Left subclavian artery B

Fig. 3-8—cont’d B, CT image, cranial thorax.

Aorta Dorsal mediastinum

Caudal lobe Left pulmonary ligament

Middle mediastinum Left lung, caudal part of cranial lobe Pulmonary pleura Parietal serous pericardium

Fibrous pericardium Pericardial mediastinal pleura Visceral serous pericardium

(epicardium) Pericardial cavity

Sternum, 5th segment Ventral mediastinum

5th rib

Parietal costal pleura Right lung, middle lobe Pulmonary pleura Plica venae cavae Caudal vena cava Accessory lobe Caudal lobe Esophagus Azygos vein 6th thoracic vertebra

Heart

A

Fig. 3-9 A, Schematic transverse section of thorax through heart, caudal view.

(Continued)

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between them. Enclosed in the mediastinum are the thymus, the lymph nodes, the heart, the aorta, the trachea, the esophagus, the vagus nerves, and other nerves and vessels. The pericardial medias-tinal pleura is that portion covering the heart.

The mediastinum can be divided into a cranial part, that lying cranial to the heart; a middle part, that containing the heart; a dorsal portion dorsal to the heart; a ventral portion, ventral to the heart; and a caudal part, lying caudal to the heart. The caudal mediastinum is thin. It attaches to the diaphragm far to the left of the median plane. Cranially, it is continuous with the middle mediastinum.

Note the passage of the esophagus through the mediastinum and the esophageal hiatus of the dia-phragm. At the esophageal hiatus, a thin layer of pleura, peritoneum, and enclosed connective tis-sue attaches the esophagus to the muscle of the diaphragm.

The plica venae cavae is a loose fold of pleura derived from the right caudal mediastinal portion of the pleural sac that surrounds the caudal vena

cava. The root of the lung is composed of pleura and the bronchi, vessels, and nerves entering the lung. Here the mediastinal parietal pleura is con-tinuous with the pulmonary pleura. Caudal to the hilus this connection forms a free border, known as the pulmonary ligament (Figs. 3-9, 3-10), between the caudal lobe of the lung and the mediastinum at the level of the esophagus. Observe this ligament.

In thoracic surgery this must be cut to reflect the caudal lung lobe cranially.

The thymus (Figs. 3-8, 3-11, 3-12, 3-14, 3-16, 3-20) is a bilobed, compressed structure situated in the cranial mediastinum. It is largest in the young

The thymus (Figs. 3-8, 3-11, 3-12, 3-14, 3-16, 3-20) is a bilobed, compressed structure situated in the cranial mediastinum. It is largest in the young

In document Universidad Autónoma de Madrid Facultad de Psicología Departamento de Psicología Social y Metodología Programa de Doctorado con Mención de Calidad (página 111-116)