Osseous System. 165 



It is possible that a habit may not appear to agree precisely with the; 

 present structure of the individual, and if it does not, it is evidently 

 working a change in such structure. It is to habit under stimulus, 

 therefore, that we look for the origin and cause of all differentiation. The 

 history of differentiation is, therefore, the history of habit, and the his- 

 tory of habit is the history of stimulus. This statement appears obvi- 

 ous on its face, but it may not be readily realized how much it implies 

 and how far it leads, which will appear, however, as we go on, with fur- 

 ther illustrations. 



FIG. 88. Skeleton of Gorilla engena. 



1 Acromion process of Scapula. 



2 Scapula. 



3 Clavicle, 



Coracoid process. 



5 Humerus. 



6 Sternum. 



7 Spine. 



8 Ilium. 



9 Sacrum. 

 H)Piibis. 

 llIschium. 

 12 Ulna. 

 13-Radiu8. 

 14 Carpal bones. 

 15Metacarpals (hand). 

 16 Phalanges (fingers). 

 17 Femur (thigh). 

 18 Patella (knee pan). 

 19 Tibia. 

 20 Fibula. 

 2lTarsal bones. 

 22Afetatarsals. 

 23 Phalanges (toes). 

 24rCcUcaneum os calcis (heel bone). 

 25 Astragalus. 



If the pelvic arch, including the 

 hip bones, &c. , had always affected 

 the same habits as the pectoral 

 arch, we should find it possessing 

 the same construction. At the 

 outset the two were much alike in 

 function, and, consequently, in 

 form. In the Selachian, or carti- 

 laginous fishes, the pelvic arch 

 consists of a pair of cartilaginous 

 plates much like those of the pec- 

 toral arch. They are, in some 

 cases, joined together in the ab- 

 dominal front, and, like those of 

 the pectoral arch, they support the 

 fins. When, in the osseous fishes, 

 the rartilnii'inous :ircli becomes 

 broken up into parts, these parts 

 correspond with those in the pec- 

 Fio.88. torul tuvh, the ilium answering to 



