ANATOMY OF VERTEBRATES. 



95 



the centrum 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 



O DO 



fixity being required in this part of the 

 skeleton, instead of the mobility and elas- 

 ticity which is needed in the vertebral 

 column of the trunk. It may be also 

 observed that the i 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 haemal arch ; and 

 that the neural spine retains much of the 

 shape of the parts so called in the trunk. 

 Nevertheless, the elements of the neural 

 arch of tins hindmost segment of the skull 

 have undergone so much developement and modification of shape, 

 that they have received special names, and have been enumerated 

 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 human skeleton all those parts are blended together 

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

 Anatomy it is the ' epencephalic arch,' because it surrounds the 

 hindmost segment of the brain called ' epencephalon.' 



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

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

 inferior or haemal 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- 



Disarticulatcd epencephalic arch, 



viewed from behind: Cod 



(Morrhua vulgaris) 



pophysis ; the upper prong, 



answering 



to the i 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 ' hamiapophy ses ; ' 

 these support diverging appendages consisting of many bones 

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

 hremal arch of the occipital vertebra are, from above downwards, 

 ' suprascapula,' 50 ; * scapula,' 51 ; ' coracoid,' 52. The inverted arch, 

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

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



