A total of 31 thymus samples collected from female goats with the age range from ten days after birth to 30 months were used for gross morphological studies. The results show that the thymus consists of thoracic, cervical and cranial lobes, which are superficially lobulated. The thoracic lobe considered as a single quadrilateral mass present in the dorsal part of the left of the pericardial mediastinum and connected to the cervical lobe by a cervicothoracic isthmus. The cervical lobe divided into right and left portions. In the caudal third of the neck, the right and left portion adhere together, forming a single caudal part called the body and cranially to diverge, forming two limbs. The cranial lobe of the thymus is ovoid in shape. The morphological changes and the arterial blood supply of the thymus gland are recorded. At group I and II, the thymus gland was well developed, and all lobes and isthmus of the thymus gland were found. At Group III thymus gland highly decreased in size, and the cranial part of the right limb of the cervical lobe was wholly involuted. At group IV and V, the right and left limbs of the cervical lobe and the isthmus were involuted entirely. At group VI the cranial lobes are completely involuted, and the thymus gland consists of the remnant caudal cervical and thoracic lobe only. At the age of 27- 30 months complete involution of the thymus gland, there was a thin remnant of the thymus gland in the cranial mediastinum and complete disappearance of the cervical lobe and replaced by adipose tissue. It was seen that the thoracic lobe of the thymus was supplied by three branches from the brachiocephalic trunk, left internal thoracic artery to give rise to pericardiophrenic artery, this artery gave a thin branch to the caudal pole of the thoracic lobe of the thymus. Cervicothoracic isthmus takes its arterial blood supply from the right internal thoracic artery. The body of the cervical lobe takes its arterial blood supply from 3-4 direct branches from the common carotid artery, and offshoots branches from arterial branches descend for the trachea and the esophagus. The cranial two limbs take its arterial blood supply from 3-4 thymic branches from the caudal thyroid artery. It also found that the cranial lobe of the thymus gland takes its arterial supply from two Indirect branches from the external carotid artery.
Key words: Adipose tissue, Caprine, Involution, Morphology, Thymus
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