THYMUS

THYMUS - OX

• The thymus is a lymphoid organ and is well developed only in the last stages of fetal life and a few months after birth
• After birth it undergoes atrophy. In the calf it is pale in colour, distinctly lobulated and consists of thoracic and cervical parts
• The thoracic part occupies the greater part of the cranial mediastinal space upto the pericardium
• Its left face is in contact with the chest wall and the left lung
• Its right face is molded on the great vessels in front of the heart
• The cervical part forms the bulk of the gland and consists of right and left lobes, which extend the ventro-lateral aspects of the trachea from the thoracic inlet to the thyroid gland
• It weighs about 435 to 600 gm. at five or six weeks of age

THYMUS - SPECIES DIFFERENCE

Sheep and Goat

• It resembles ox

Horse

• In the newborn foal it is greyish pink and consists of right and left lobes
• The greater part of the gland is situated in the cranial mediastinum but the two lobes are continued into the neck by a chain of lobules, which lie on the trachea along the course of the carotid artery extending sometimes as far as the thyroid gland
• The cervical part however is very variable

Pig

• In young ones, it is very large extending to the larynx or even to the mandibular space

Dog

• It is small and situated almost entirely in the thoracic cavity
• The left lobe is larger than the right

Rabbit

• As in ox

Fowl

• The thymus is well developed in young chicks; the lobules are extending along the neck on either side