<prompt> According to the servosystem theory of growth, which of the following hormones controls the growth of the primary cartilage?Growth hormoneSomatomedin hormoneSex hormonesThyroxine  <response>: According to servo system theory, the midface grows downward and forward under the primary influence of the cartilaginous cranial base and nasal septum, influenced principally by the intrinsic cell-tissue related properties common to all primary cartilages and mediated by the endocrine system. The influence of somatotrophic hormone on the growth of cartilages of nasal septum, spheno-occipital synchondroses and other synchondroses follows that of a cybernetic form of command pattern. Textbook of craniofacial growth, Sridhar Premkumar 