anatomical and histomrphometrical study of thymus in maquee sheep’s fetus

anatomical and histomorphometrical study of sheep’s thymus was conducted by 75 apparently healthy fetuses that collected from urmia’s industrial slaughterhouse. after anatomical study, the samples were fixed in 10% formal saline, passaged and histological paraffin sections prepared in 5-7 μm in thickness, and by h&e; method stained. histomorphometrical study performed by graded and latticed lens devises. results of anatomical study showed that thymus begin to develop from cranial part of pericardium in the left side of cranial mediastinum and the ventral surface of neck, and it extend to ⅓ caudal part of neck, then it bifurcate to right and left sides and gain to the pharynx. histomrphometrical study showed that, mean thickness of thymic lobules in thoracic part at 2nd month of fetal period, significantly was greater than the neck part, whereas, in 2nd half of 4th month in neck part it showed significantly increase(p<0.05). mean thickness of cortex and medullae of lobules, from 2nd month until 2nd half of 3rd month in thoracic part was greater, but after that time, until 5th month it was significantly greater in neck part(p<0.05). mean thickness of trabeculae decrease as fetus developing. mean distribution of hasal’s corpuscles from 3rd month until 5th month were increased, but, mean thickness of these corpuscles were increased until 4th month. this study showed that mean thickness of cortex and medullae of lobules were not significantly different in all fetal periods.