ANATOMY OF VERTEBKATES. 95 



the ceiitnim of the first vertebra of the trunk : the opposite 

 surface is also concave, but expanded and very irregular, in order 

 to effect a much firmer union with the centrum of the next cranial 

 segment in advance — great strength and 

 fixity being required in this part of the 

 skeleton, instead of the moljility and elas- 

 ticity which is needed in the vertebral 

 column of the trunk. It may be also 

 ol)served that the ' neurapophyses ' are per- 

 forated, like most of those in the trunk, 

 for the passage of nerves ; that the diapo- 

 physes give attachment to the bones which 

 form the great inferior or liromal arch ; and 

 that the neural spine retains much of the 

 shape of the parts so called in the trunk. 



-.^■^^ /•! 1 Disarticulated epencephalie arclj, 



JN evcrtheless, the elements ot the neural Tiowtatrombehiua: coa 

 arch 01 this Inndmost segment oi the skull 



ha^'e undergone so much dcvclopement and modification of shape, 

 that they have received special names, and have been enmnerated 

 as so many distinct and particular bones. The centrum, i, is 

 called ' basioccipital ; ' the neurapophyses, 2, ' exoccipitals ; ' the 

 neural spine, 3, ' superoccipital ; ' the diapophyses, 4, ' parocci- 

 pitals.' In the Iiuman skeleton all those parts are blended together 

 into a mass, which is called the ' occipital bone.' In Philosophical 

 Anatomy it is the ' epenceplialic arch,' because it surroimds the 

 liindmost segment of the brain called ' epencephalon.' 



The entire segment, here disarticulated, is called the ' occipital 

 vertebra,' and in it we have next to notice the widely-expanded 

 iirferior or ha3mal arch, fig. 81, 50, H. This consists of three 

 pairs of bones. (The first pair are bifurcate, and have two points 

 of attachment to the neural arch, the lower prong, answering to 

 what is called the ' head of the rib,' abutting upon the neura- 

 pophysis ; the uj)per prong, answering to the ' tubercle of the 

 rib,' articulating to the diapophysis. -, (The second pair of bones 

 are long and slender, and represent the body of the rib.' The 

 first and second piece together answer to the element called 

 ' pleurapophysis ; '(the third pair of bones are the ' hajmapophyses ; ' 

 these support diverging appendages consisting of many bones 

 and rays. ) The special names of the above elements of the 

 hjemal arch of the occipital vertebra are, from aliove downwards, 

 ' suprascapula,' so ; ' scapula,' 51 ; ' coracoid,' 52. The inverted arcli, 

 so formed, encompasses, supports, and protects the heart or centre 

 of the haemal system; it is called the 'scapular arch.' There 



