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VERTEBUATE ANIMALS. 



In the typical vertel>i'a the segment is completed by a second 

 arch, wliich is ]ilaced in front of or beneath the body of the verte- 

 lu'a., and "which is known as the "luoiial' arch, as it includes and 

 imitects the princii)al organs of the blood-circulation (tig. L58, B). 

 This second arch is often (inly rci-oginsablc W'itli great difficulty, as 

 its pai'ts are generally much modified ; but 

 a gooil example may l>e obtained in the 

 human thorax. Here, attached to the front 

 of the vertelira"', we tiial a series of bony 

 arches, known as the ribs (r), followed by a 

 s/rics of cartilaginous pieces of a similar 

 sliajie, tcrme<l the "costal cartilages" (p), the 

 whole united in front by a central bone, 

 known as the breastbone or "sternum" (i). 

 As a general rule, amongst the higher 

 Vertebrates, the follown'ng regiiiiis may be 

 recoginseil in the verteljral cohunn : Firstly, 

 the r.-rn'riil nr/imi (tig. lo!), r), coni])rising a 

 variable mimber of vertelme, which con- 

 stitute the neck, and immediately follow 

 the heail. Secondly, the cervical region is 

 succeeded by a variable number of vertebne 

 ^^■hich usually carry ribs, and are known as 

 (lie ihirxiil vertebra- (d), or vertelme of the 

 liack. ^J'liirdly come certain vei'tel)r:e wdiich 

 ennstitule the hiiiihar region (/), or the 

 regicai of the loins. Fourthly, there usually 

 follows a series of vertebr;e which are im- 

 movably nnited together to form a single 

 bone, which is termeil the xiuTtim (.<). 

 Lasth% there conies a "\';iriable sei'ies of 

 ■\'(U'teln'a' which are usually free anil mov- 

 .able U]iou one .•mother, and which con- 

 stitute the iiiiiiiUil region, or the region of 

 the tail (/). 



The nature of the l)ones which enter into 

 the covu|iosition of the lindis varies somewhat 

 ill dilferi'iit Vertebrates in accord.ance with 

 their mode of life ; but in all the higher 

 members of the subd<iiigdiim tin' biiibs are built upon a general and 

 easily recognisable type. The fore-limb i-oiisists gener.ally of the 

 fullowing jiaits : I , .A series of lunies uniting the limb to the trunk, 

 llie two most ilii|.oit:ilit being (liesliiaililei--blade(.sv,(/)»/o, hg. 160, .s-) 

 and (he rnrnraiil^ while a eollar-biine (f/nn'r/r') may .also bc^ present. 



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