Sheep is a widely used model of human fetal development. The object of this study was to clarify the typical architecture and morphological variations of the cervical sympathetic trunk and ganglia in the sheep during fetal period. Also cervical sympathetic trunk components were examined qualitatively to determine their normal fetal growth rates and patterns in different gestational ages. Eighty sides of 40 sheep fetuses aged from 60-140 days (23 male and 17 females) were assigned to 4 groups of 10 animals and components of bilateral cervical sympathetic trunk of were examined under a stereomicroscope and Sex liner measurements of cervical sympathetic trunk components were done using a digital caliper.
Morphology: Constant cranial cervical ganglion and two or three inconstant middle cervical ganglion were noted. The skelototopy and frequency of presence of the cranial cervical ganglion, the syntopy of cervical ganglia, and composition and course of the vagosympathetic trunk were consistent among the specimens whereas the shape of ganglia, the skelototopy and frequency of two or three middle cervical ganglia, and the frequency of communicating branches of cranial cervical ganglion to the first cervical spinal nerve exhibited differences during fetal period. The morphological data achieved in cervical sympathetic trunk and ganglia of fetal sheep extremely different from that in humans and is difficult to apply and translate directly to humans because of more cranial position of cranial cervical ganglion, very narrow contribution of cranial cervical ganglion to cervical spinal nerve, lack of vertebral ganglia, existence of multiple cervical ganglia, and no communicating branch from middle cervical ganglion to the cervical spinal nerve.
Morphometry: (1) There was no gender and laterality difference in growth of the cervical sympathetic trunk components in sheep during fetal period except: gender and laterality differences in length of cervical sympathetic trunk and laterality differences in the total length of inter ganglionic branch and width of first middle cervical ganglion and theses values were greater in left sides than in the right. (2) Correlation coefficients between dimensions of cervical sympathetic trunk components and CRL were always positive during fetal period and decreased with increasing fetal age (3) The highest growth rate in cervical sympathetic trunk in fetal sheep took place in the youngest age group because of rapid growth rates in the lengths of interganglionic branch and cranial cervical ganglion. Based on these detailed findings, comparative prenatal growth rates and patterns of cervical parts of sympathetic trunk were discussed and compared with previous studies.