Cope.] ^''^ [Dec. 2, 



These are, articular facets, osseous deposit at presumed points of irrita- 

 tion from various stimuli, and the development of bone at ligamentous 

 and tendinous insertions. To the combination of the causes which pro- 

 duce the first and second effects we owe most of the secondary pecu- 

 liarities of the vertebrate skeleton ; and to the third we owe the funda- 

 mental construction of the skeleton on which the secondary modifications 

 have been superposed. It is not important to our contention if the his- 

 tological structure of some of the abnormal osseous deposits in our speci- 

 men may differ slightly from the normal tissues sought to be explained by 

 it. This may be accounted for by the difierent circumstances to which the 

 two sets of phenomena are due. In the dislocation the change from the 

 antecedent state of the parts is violent and abrupt. In the evolution of 

 the vertebrate skeleton the process was slow and gradual. In the cases 

 of the luxations nature had to meet the changed conditions by correspond- 

 ingly abnormal measures. In orderly evolution " saltus non fecit." It 

 may, however, be justly inferred, that if such characteristic structures 

 can be produced in the space of mouths, how much more easy has it been 

 for stimuli of allied character to develop the features of normal articula- 

 tions during the ages of geologic time. 



We have here, also, an instructive lesson as to the matter of inheritance. 

 Every one knows that mutilations, luxations, etc., are not usually inherited. 

 This is because they are not "acquired " in the proper sense of the word. 

 Since characters truly acquired are inherited, it is evident that a long con- 

 tinuance of the stimulating cause is necessary to produce a true acquisi- 

 tion. The difference between a character produced by causes apart from 

 tlie normal life of an animal and not repeated, and those produced by 

 causes operating daily and hourly for geologic ages, is necessarily very 

 great. And, as Prof. Scott* remarks, the latter have not been acquired 

 during the lifetime of each generation, since they are found in the young 

 before birih, before external stimuli have had the opportunity to exert 

 their influence. 



Explanation of Plates. 



Figs. 1-5. Homo sapiens, luxated elbow joint ; one half natural size. 



1. Luxated elbow joint, from within. 



2. Luxated elbow joint, from outer side. 



3. Humerus, posterior view of distal region. 



4. Humerus, distal view. 



5. Ulna and radius, anterior (superior) view. 



Lettering. — H, humerus ; U, ulna ; R, radius ; C, coronoid process ; C?, 

 second (abnormal) coronoid process ; 0, olecranon ; E)i, entepicondyle ; 

 Ec, ectepicondyle ; E)io, entepicondylar exostosis ; Eco, ectepicondylar 

 exostosis ; Co, condylar exostosis ; Cos, superior condylar exostosis ; Coi, 



* "On the Osteology of Mcsohippus and Lcptomcryx," American Journal of Morphology , 

 1891, p. 385. 



