According to the servosystem theory of growth, which of the following hormones controls the growth of the primary cartilage?
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
Growth hormone
Somatomedin hormone
Sex hormones
Thyroxine