G28 EMBRYOLOGY. 



of the trunk sustain to each other in the morphology of Vertebrates 

 was for the first time subjected to a thorough scientific discussion 

 at the beginning of the present century, when the school of the 

 " Natural Philosophers " began its career. An attempt to solve the 

 problem was made in very similar ways by two persons, by the 

 natural philosopher OKEN and by the poet GOETHE, without either 

 of them having been influenced by the other. 



According to the OKEN-GOETHE vertebral theory, the skull is the 

 most anterior part of the vertebral column, and is composed of a 

 small number of modified vertebrae. OKEN distinguished three 

 vertebra? in his " Programme " entitled " Ueber die Bedeutung der 

 Schadelknochen," which appeared in 1807, when he entered upon a 

 professorship conferred upon him in Jena. He named them the 

 ear-, eye-, and jaw-vertebra?. 



Each head-vertebra, like a trunk- vertebra, consisted in his opinion 

 of several parts a body, two arch-pieces, and a dorsal spine. OKEN, 

 GOETHE, and their numerous followers believed that this composition 

 was most distinctly recognisable in the last cranial vertebra, the 

 OGcipitcde, the base of which was compared to the body of the 

 vertebra, the condyloid parts to the lateral arches, and the squama 

 to the spine of the vertebra. 



A second cranial vertebra was discerned in the body of the %)os- 

 terior sphenoidale, which together with its greater wings and the 

 two parietal bones formed a second bony ring around the brain. 



A third vertebra was constructed out of the body of the sphenoidale, 

 anterius, the lesser wings and the frontale. 



The ethmoidale was cited by many investigators as a fourth the 

 most anterior cranial vertebra. A number of bones, which would 

 not fit into this scheme, were considered to be structures sui generis, 

 and were in part associated with the sensory organs as sensory bones, 

 in part compared with the ribs of the thorax. 



In this form, which underwent numerous modifications in details, 

 the OKEN-GOETHE vertebral theory of the cranium dominated mor- 

 phology for decades and formed the foundation of many investiga- 

 tions. It had a stimidating and fruitful effect until, with a deeper 

 insight into the structure of Vertebrates, it was abandoned as defective 

 and erroneous, giving way before the force of numerous newly dis- 

 covered facts. 



For neither the comparative osteology of the skull nor growing 

 embryological research could point out in a satisfactory way which 

 bones were really to be interpreted as parts of vertebrae. The most 



