CHAPTER XXII. 



DEVELOPMENT OP THE OEGANS OF MOTION. 



The Motive Apparatus of Vertebrates. — These are constitTited by the 

 Passive and Active Organs of Motion (Skeleton and Mnscles). — The 

 Significance of the Internal Skeleton of Vertebrates. — Structure of the 

 Vertebral Column. — ^Formation and Number of the Vertebrse. — The Ribs 

 and Breast-bone. — Germ-histoiy of the Vertebral Column. — The Noto- 

 chord. — The Primitive Vertebral Plates. — The Formation of the Meta- 

 mera. — Cartilaginous and Bony Vertebrae. — Intervertebral Discs. — 

 Head-skeleton (SkuU and Gill-arches). — Vertebral Theory of the Skull 

 (Goethe and Oken, Huxley and Gegenbaur). — -Primitive Skull, or 

 Primordial Cranium. — Its Formation from Nine or Ten Coalescent 

 Metamera. — The Gill-arches (Riba of the Head). — Bones of the Two 

 Pairs of Limbs. — Development of the Pive-toed Foot, adapted for 

 Walking, from the Many-toed Fin of the Fish. — The Primitive Fin 

 of the Selachians (Archipterygium of Gegenbaur). — Transition of the 

 Pinnate into the Semi-pinnate Fin. — ^Atrophy of the Bays or Toes 

 of the Fins. — Many-fingered and Five-fingered Vertebrates. — Com- 

 parison of the Anterior Limbs (Pectoral Fins) and the Posterior Limbs 

 (Ventral Fins). — Shoulder Girdle and Pelvis Girdle. — Germ-history of 

 the Limbs. — Development of the Muscles. 



" In forming his estimate of my entire theory, the reader may begin with 

 the details and examine the fundamental facts on which I base my con- 

 clusions. But it is equally necessary to connect the detached facta, and 

 estimate their bearing on the whole. He who in the world of organisms sees 

 only disconnected existences, in which some organic similarities appear as 



