THE INHERITANCE OF FAMILY TRAITS 173 



occurrence two or more times in one family. Either father 

 or mother of an affected child may be affected; or they 

 may have symmetrical spines themselves but have an af- 

 fected brother or sister. The offspring are bom with an 

 hereditary laxness and weakness of the constituent parts 

 of the spinal column and its ligaments, so that the column 

 easily falls into lateral curves under the influence of second- 

 ary causes. 



c. Exostoses. — ^Upon the long bones there occasionally 

 develop osseous outgrowths known as exostoses. The method 



■p 



aUo 



DO BiO 



N I SCO. ExA4ijr5. 

 Fig. 154 



some affected Ex.Uifrs. 



Fig. 155 



Fig. 154. — Pedigrees of exostoses on the long bones. Affected individuals 

 represented by black symbols. Exj exostoses, sex unknown; sco, scoliosis or 

 spinal curvature. Teissier and Denecham, 1905. 



Fig. 155. — Part of a pedigree of exostoses on the long bones that have been 

 traced through 6 generations. Exj exostoses, sex unknown. Mery and 

 Metayer, 1905. 



of inheritance of the tendency to produce such growths is 

 indicated by pedigrees given in Figs. 154, 155. 



d. Absence of Clavicles. — ^The collar bones, or clavicles, 

 are occasionally imperfectly developed and the tendency to 

 this result shows itself in several members of one family. 

 This is well illustrated by a case described by Carpenter 

 (1899) Fig. 156. The high incidence of the abnormal condi- 

 tion in this family suggests that the defect is due to a positive 

 inhibitor. 



