336 



ZOOLOGY 



SECT. 



Reptiles, the first pair (epiplastra) to the clavicles, the others pro- 

 bably being of the same character as the abdominal ribs of the 



Crocodilia. 



The carapace of 

 the Lu t h or 

 Leather-backed 

 Turtle (Dermato- 

 chelys orSphargis) 

 is distinguished 

 from that of the 

 rest of the order 

 in being composed 

 of numerous poly- 

 gonal discs of bone 

 firmly united to- 

 gether, and in not 

 being connected 

 with the endo- 

 skeleton ; in the 

 plastron the 

 median bone is 

 absent. 



Carapace and 

 plastron are firmly 

 fixed together by 



Flo. 997. Cistudo lutaria. Skeleton seen from below ; the A 



plastron has been removed and is represented on one side, m O S t instances, 



C. costal plate ; Co. coracoid ; e. entoplastron (episternum) ; 1+ c,^i^ c, +1^ 



Ep. epiplastron (clavicle ?) ; F. fibula ;Fe. femur ; H. humerus ; Dut Sometimes tne 



Hyp. hyoplastron ; Hpp. hypoplastron ; Jl. ilium ; Js. ischium ; rormprtinn i<i lio-a 



M. marginal plates: Nu. nuchal plate ; Pb. pubis ; Pro. pro- 



coracoid or process of scapula ; Py. pygal plates ; R. radius ; Sc. mentoUS. 



scapula ; T. tibia ; U. ulna ; Xp. xiphiplastron. (From mi 



zittei.) The sternum m 



the Lacertilia is a 



plate of cartilage with a simple or bifid posterior continuation 

 formed by the fusion of five or six pairs of ribs. In the Ophidia 

 and Chelonia it is absent. 

 In the Crocodilia it is a 

 broad plate bearing the 

 coracoids and two pairs of 

 ribs with a posterior con- 

 tinuation which bifurcates 

 behind. 



A series of ossifications 

 the abdominal ribs lie 

 in the wall of the ab- 

 domen in the Crocodilia 

 (Fig. 994, Sta), and similar ossifications occur also in the Moni- 

 tors and in Sphenodon. As already noticed, the posterior 



FIG. 998. Chelone midas. Transverse section of 

 skeleton. C. costal plate ; C. 1 centrum ; M. mar- 

 ginal plate ; P. lateral element of plastron ; R. rib 

 V. expanded neural plate. (After Huxley.) 



