OSSEOUS SYSTEM. (Coup. AKAT.) 



827 



Fig. 437. 



17 



Hyoid apparatus and branchiostegous rays of Perch (after Cuvier). 



proper to examine bow far it is entitled to be 

 looked upon as we have already stated it to be, . 

 as forming a continuation of the spinal column, 

 and if so, to define the vertebrae of which it 

 consists. In the human cranium indeed this 

 would be no easy task, partly in consequence 

 of the extreme exaggeration of every element 

 composing it, and partly from the manner in 

 which some bones, distinct in the lower animals, 

 are here consolidated into single masses ; more- 

 over in consequence of the prodigious develope- 

 ment of the cerebral hemispheres every part is dis- 

 torted and pushed aside as it were out of its pro- 

 per situation relative to the neighbouring bones. 



In the cranium of the Reptile, however, and 

 even of the less intelligent Mammalia, these 

 difficulties are to a great extent done away with, 

 and the vertebral form is preserved, while, in 

 addition, the elements composing them fre- 

 quently remain permanently disunited. 



The first cranial vertebra (commencing from 

 behind) is the occipital, and this can present 

 no difficulty. In Fishes, indeed, and in many 

 Reptiles, the occipital bone, of which this ver- 

 tebra is entirely made up, has not only the 

 exact shape of one of the spinal bones, but the 

 elements composing it remaining often perma- 

 nently disunited, they are most easily and 

 satisfactorily identified. Inferiorly there is the 

 body (or basilar bone, 5) connected with the 

 body of the first spinal vertebra in the same 

 manner as the corresponding portion of the 

 other vertebrae are connected with each other. 

 On each side the neurapophyses (or extra-occi- 

 pital bones, 10J arching over the commence- 

 ment of the spinal cord, and lastly, the neuro- 

 spine (or supra-occipital bone, 8) occupying its 

 normal situation, and in many of the lower 



Vertebrata forming a real spinous process, 

 although in the human subject, owing to the 

 prodigious size of the hinder part of the ence- 

 phalon, it is enormously spread out in propor- 

 tion to the dimensions of the parts it protects. 



The second or parietal vertebra of the cra- 

 nium is slightly more distorted, and its real 

 nature masked, particularly in the higher Ver- 

 tebrata, by the interposition of the petro-tem- 

 poral bone, which does not normally belong 

 to the cranium, between it and the preceding. 

 Its body is the sphenoid bone, represented in 

 the human subject by the posterior part of the 

 sella Turcica, but which in Reptiles is a dis- 

 tinct element of the skull ; its arches are 

 formed by the alie majores of the sphenoid, 

 (likewise separate pieces of the cranium in the 

 lower animals, although in man they are con- 

 solidated with the former,) while the spine is 

 converted into the expanded parietal bone or 

 bones spread out over the central regions of 

 the brain. 



The anterior cranial vertebra is called the 

 frontal, receding still more from the normal 

 appearance of a vertebra than the parietal, the 

 preponderance of magnitude in the different 

 elements that form it being completely in- 

 verted, the body being quite rudimentary, 

 while the enormously developed spinous ele- 

 ments are now converted into frontal bones. 

 In man its body and its arches are represented 

 by the alee miraores of the sphenoid or ingrtissiul 

 bones, and the osfrontis constitutes its dispro- 

 portionately expanded spine. These three 

 vertebrae, therefore, are the essential consti- 

 tuents of the skull ; and, although in the hu- 

 man cranium the most aberrant of any met 

 with in creation, their nature is not at once 



