VAN 121: Veterinary Gross Anatomy-II (2+2)

THORAX (EXTERIOR)

Dissection

• Clean the area over costal cartilages and locate the rectus thoracis. Reflect the serratus thoracis downwards to its origin.
• Rectus thoracis: It is a thin quadrilateral muscle covering the lower part of the first few ribs and their cartilages. It arises from the lower half of the lateral surface of the first rib and is inserted to the cartilage of the third or fourth rib.
• Serratus dorsalis anterior: It is under the serratus cervicis; its aponeurotic tendon arises from the dorsal fascia. Its fleshy part has three digitations, which are inserted to the anterior borders and lateral surfaces of fifth, sixth and seventh ribs.
• Serratus dorsalis posterior: It is under the latissimus dorsi muscle. Its aponeurotic tendon arises from the lumbodorsal fascia. Its fleshy part has three digitations, which are inserted to the posterior borders and lateral surfaces of the last three ribs. Its fibres run downward and forward.

Dissection

• Cut the insertions of both the muscles and reflect them towards their origin.
• Longissimus costarum: It covers the vertebral ends of the ribs. It has lumbar and costal parts. It arises from the lateral angle of the ilium, lumbar transverse processes, anterior borders and external surfaces of the last six or seven ribs. It is inserted to the posterior borders of all the ribs and the transverse process of the last cervical vertebra.
• Longissimus dorsi: It is the longest and the largest muscle on the dorsal aspect of the spine placed above the preceding. It arises from the crest and the lateral angle of the ilium, summits of the sacral, lumbar and dorsal spines and the supraspinous ligament. It is inserted to the transverse and the articular processes of lumbar vertebrae, transverse processes of dorsal vertebrae and the lateral surfaces of the dorsal vertebrae.
• At the level of 10^th rib, it divides into dorsal and ventral divisions. The dorsal part passes deeper to complexus and is inserted to the spine of the last three or four cervical vertebrae. The ventral part passes over the origin of the complexus and is inserted to the transverse processes of the last four cervical vertebrae.
• Supraspinous ligament: It is made up of elastic tissue and extends over the summits of the spines from the sacrum to the occipital. It consists of a dorsolumbar part and a cervical part. The cervical part or the ligamentum nuchae has been examined during the dissection of the neck. The dorsolumbar part arises from the sacral spines and is attached all along its course forwards to the summits of the lumbar and dorsal spines. From the third dorsal vertebra, it spreads on the lateral aspects of the summits of the spines and from the spine of the first dorsal it is continued as the ligamentum nuchae.

Dissection

• Cut longissimus costarum and longissimus dorsi muscles at the level of the tenth rib by a vertical incision. Reflect them forward by cutting their origins upto the level of the sixth rib. Now cut the origin of complexus from the tenth dorsal vertebra and reflect it forwards. Clean the muscles covering lateral aspect of the dorsal spines and upper most parts of intercostal spaces in this area.
• Multifidus dorsi: It consists of the oblique bundles directed upwards and forwards covering the lateal aspects of the spines. The bundles arise from the transverse processes of dorsal vertebrae and pass over two or three spines and are inserted to the lateral faces of the spines in front.
• Levatores costarum: It consists of 10-11 small oblique bundles situated at the upper part of the intercostal spaces. Each bundle arises from the transverse process of dorsal vertebra, runs downward and backward to be inserted to the anterior border of the rib behind.
• Dissection: Clean the sixth intercostal space. Cut in its middle the origin and insertion of the external intercostal about 5 cm. in length and by two more cuts above and below in the muscle substance carefully, make a rectangular window. Locate the internal intercostal and make a similar window. Note the subserous tissue and costal pleura. Make a rectangular window in their pleura. Note the plelural cavity and see the pulmonary pleura.
• External intercostal: They occupy the intercostal spaces. Each arises from the posterior border of a rib and is inserted to the anterior border and external surface of the rib behind. The fibres run downard and backward.
• Internal intercostal: They are placed under the preceding. Each arises from the anterior border of a rib and its cartilage except the first and is inserted to the posterior border of the rib and its cartilage in front. The fibres run downward and forward.