T.UN(;S. ALIMENTARY CANAL. 409 



lower, are covered by cutting horny plates, like the beak of 

 a bird, which enable some species to bite with great vigour and 

 to inflict considerable wounds. 



Both sternum and sternal ribs are absent. 



The four limbs enable the Chelonia to creep and run on land ; 

 in the aquatic forms, however, they are swimming feet or fins. 

 The position of the pectoral and pelvic girdles between the 

 carapace and plastron is remarkable (Fig. 229), but in the foetus 

 they are placed, respectively, in front of and behind the ribs, 

 and only become covered by the latter as development proceeds. 

 In the pectoral girdle the scapula, the upper end of which is 

 attached by cartilage or ligament to the first costal plate, and 

 precoracoid are ossified continuously and form one bone {Sc, 

 Pco). The coracoid (Co) is distinct. The precoracoids and 

 coracoids do not form a ventral symphysis but are connected by 

 ligament. There is no clavicle, unless the epiplastra can be 

 called such. The fore limb is typical. The manus has five digits 

 and the carpus consists of the typical nine ossicles, but there is 

 sometimes a certain amount of fusion. In the pelvis the ilia 

 unite with the sacral ribs, and in some genera by ankylosis with 

 the last costal plates. There is a pubic and ischiadic symphysis, 

 but the pubes and ischia are separate ventrally (Fig. 229, Pb, 

 IS). The hind limb has five digits, and the tarsus contains the 

 usual bones, but it is less typical than the carpus and there is 

 generally a certain amount of fusion amongst its elements. 



The tongue is attached to the floor of the buccal cavity and is 

 not protrusible. The lungs are highly developed spongy struc- 

 tures attached by their whole length to the inner surface of the 

 shell. They are covered on their ventral surfaces by a muscular 

 diaphragm-like membrane, which is attached to the bodies and 

 ribs of the third and fourth dorsal vertebrae. The respii'atory 

 movements of air are caused, partly by the protrusion from and 

 retraction into the shell of the head and limbs, and partly by 

 swallowing movements in which the hyoid apparatus partici- 

 pates. They can usually exist a long time without breathing. 



A membranous epiglottis is sometiixies present. There are no ^'ocal 

 chords, but some Chelonia have a feeble piping voice. In the genus 

 Ciny.vis the trachea and bronchi are curved. 



The intestine is without a caecum. The cloaca contains, at- 



