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

PECTORAL REGION

• Dissection of the forelimb is begun with the animal on its back, as it is necessary to dissect the pectoral region and axilla first to help the dismembering of the limb later.
• Examine the pectoral region, which is rounded and prominent, formed by the superficial pectoral extending from the forepart of the sternum to the limb.
• Their anterior border can be marked in front of the shoulder where they unite with brachiocephalicus and their posterior border is marked by a fold of skin.
• On the median line, there is a median pectoral groove separating the pectorals of either side.

Dissection

•  Make a straight incision on the median pectoral groove extending the whole length of the sternum.
• Make another transverse incision from the medial aspect of the elbow to join the former.
• Reflect the two flaps of the skin away from the incisions. Clean the superficial pectorals taking care to preserve the Cephalic Vein in front.
• There is a shallow transverse groove separating the anterior and posterior superficial pectorals.
• Cephalic vein: This vein, formed by the union of medial metacarpal vein with the dorsal metacarpal vein, ascends and passing in the groove between the brachiocephalicus and anterior superficial pectoral terminates by joining the external jugular vein in front of the thoracic inlet.
• Anterior superficial pectoral: This is a small thick muscle extending from the ventrolateral aspect of the forepart of the sternum to the anterior edge of the humerus where it unites with the brachiocephalicus.
• Posterior superficial pectoral: This is a small thick muscle extending from the ventrolateral aspect of the forepart of the sternum to the anterior edge of the humerus where it unites with the brachiocephalicus.

Dissection

• Cut the Superficial pectorals close to their origin from the sternum taking care to perserve their nerve and artery which are ramifying on their deep face.
• The muscles are gently reflected towards the limb and the nerve and artery supplying them to be noted.
• Nerve and artery to Superficial pectorals: A pectoral nerve from the brachial plexus and an artery, which is a branch of external thoracic artrey, enter the deep face of the superficial pectorals at their anterior border and supply them. These should be carefully secured and followed after reflecting the pectorals by cutting their origin from the sternum.

Dissection

• Clean the deep pectoral and note pectoral never from the brachial plexus supplying it.
• Define its anterior and posterior borders. In front of its anterior border, note a small bundle of muscle-subclavius and inferior cevical artery and its posterior broder is overlaped by the cutaneous muscle of the trunk and note emerging from this border, the external thoracic nerve.
• Deep pectoral: It is very large and extensive arising from the inferior part of the sternum and tunica abdominialis. The muscle passes upwards and forwards and is narrow at its insertion to the medial tuberosity of the humerus where it is covered by the brachiocephalicus.
• Subclavius: It is a small red bundle of muscle arising from the cartilage of the first rib blending with the deep face of the brachiocephalicus in front of the shoulder.
• Inferior cervical artery: It is a branch of the brachial artery arising from it at the anterior border of the first rib, which may not be seen at this stage. The artery passes between the brachiocephalicus and omotransversarius, supplies them and the prescapular lymph gland and finally terminates by supplying the lower part of the supraspinatus.
• External thoracic nerve: At this stage its origin from the brachial plexus and its course cannot be seen. Its emergence along the poterior border of the deep pectoral and its passage on the deep face of the cutaneous muscle can be seen. Rarely a small vein may be seen along its upper border.