284 ON THE STRUCTURE OF THE VERTEBRATE SKULL. 



"Between the sphenoid and occipital bones, between the 

 sphenoid and petrous bones, between the parietals (the tem- 

 poral bones are away) and the occipital bone, draw a line, and 

 you have marked off the first vertebra. Draw another line 

 between the two sphenoids, or, in Man, in front of the ptery- 

 goid processes ; laterally, through the fissura orbitalis in front 

 of the aide magnse ; lastly, between the frontals and the parietals, 

 and you have the second vertebra separated from the last. 



" 1. Now, take the ear vertebra of a foetus of any Mammal 

 or of a Man ; place beside it an incompletely-developed dorsal 

 vertebra, or the third cervical vertebra of a Crocodile, and 

 compare the parts of which the two are composed — their forms, 

 their contents, and the exits of the nerves. 



" According to Albinus and all anatomists, each vertebra 

 of a fcetus consists of three separate pieces — the body and the 

 two arches, which together form the spinous, transverse, and 

 oblique processes. You have the same in the occipital bone, 

 only more distinct and separate. The pars basilaris is a 

 corpus vertebrae still more separated from the condyloid parts, 

 which form the lateral regions ; these are again separated 

 from the pars occipitalis, which forms the spinous process. In 

 fact, this part itself is often split again, like the spinous pro- 

 cesses in spina bifida. The occipital bone, therefore, is decom- 

 posable, according to the mode of its origin, into five pieces, 

 since the lateral, or articular, and the spinous parts appear as 

 independent developments ; as is found also in actual vertebra?, 

 which consist of five pieces, and in the third cervical vertebra of 

 the Crocodile. Finally, I need take no further pains to prove 

 that the occipital foramen is the lower aperture of a vertebral 

 canal ; that the foramen lacerum is an inter-vertebral foramen, 

 and the occipital protuberance is a spinous process ; that, there- 

 fore, the occipital bone, in respect of form, as of function (since 

 it encloses the cerebellum, as a continuation of the spinal 

 marrow), is in every sense a true vertebra, since the mere 

 naming of these parts is enough to cause their recognition as 

 such. 



" You will think T have forgotten the petrous bone. No ! 

 It seems not to belong to the vertebra? as such, but to be the 



