ABSTRACT
Histogenesis and histomorphometric studies of skin from regions of the face, neck, shoulder and fore-limb were carried out on 75 healthy sheep fetuses, which were collected from Urmia slaughter-house. After measurement of the crown-rump [CR] for determining the age of fetuses, tissue specimens were collected and fixed in 10% buffer formal saline, processed and sectioned into 5-7 micro m thick layers. The sections were stained with H and E method and observed by graduated objective lens. To study the reticular, elastic and collagen fibers and mast cells, appropriate staining methods such as PAS, Verhoeff, Van Gesson and toluidin blue were used, respectively. This study showed that the differentiation of epidermis begins from the end of the second month and rate of epidermal growth in the hind-limb was more than that in other regions studied. Melanocytes appeared in 61-65 days of fetal period in epidermis. The hair follicles were seen as cell accumulations in epidermis that protruded toward dermis in the first half of the third month. The hair follicles growth rate was found to be more in the hind-limb and less in shoulder than that in the other regions studied. Sebaceous and sweat glands appeared from the second half of the third month. They quickly increased in the first half of the fourth month in all studied regions. The sweat glands growth rate on the hind-limb was more than the other sites. The growth of sebaceous glands in shoulder continued till the fifth month. The relationship between thickness of epidermis and its cell layer numbers in all areas were significant [P<0.05] and their correlation coefficient [r = 0.78] in the hind-limb was more than that observed in other regions studied. Collagen fibers appeared during 65-75 days of fetal life, and their accumulation in deep regions of dermis [90-95 days] caused differentiation of dermis to papillary and reticular layers. Reticular and elastic fibers appeared during 55-60 and 70-75 days of fetal life, respectively. Mast cells were scattered in deep regions of dermis in fifth month of fetal period