STRUCTURE OF CROCODILES 



711 



the neural arch and the centrum persist at least for a long time. 

 Chevron bones are formed beneath the centra of many of the caudal 

 vertebrae. 



Many of the ribs have two heads — capitulum and tubercle — by 

 which they articulate with the vertebrae. From seven to nine of the 

 anterior dorsal ribs are connected with the 

 sternum by sternal ribs, and from several 

 of these anterior ribs cartilaginous or 

 partially ossified uncinate processes project 

 backwards. The so-called abdominal ribs 

 have nothing to do with ribs, but are 

 ossifications in the fibrous tissue which hes 

 under the skin and above the muscles. 

 They form seven transverse series, each 

 composed of several ossicles. 



As to the skull (Figs. 419, 423), there is 

 an interorbital septum with large alisphen- 

 oids ; the presphenoid and orbitosphenoids 

 are at best incompletely ossified ; all the 

 bones are firmly united by persistent 

 sutures ; both upper and lower temporal 

 arcades are completely ossified ; the 

 maxillae, the palatines, and the pterygoids 

 meet in the middle line of the roof of the 

 mouth, covering the vomers, and deter- 

 mining the position of the posterior nares 

 — at the very back of the mouth ; an os 

 transversum or transpalatine extends be- 

 tween the maxilla and the junction of 

 palatine and pterygoid ; a postorbital rod 

 (epipterygoid or columella) is formed by a 

 downward process of the postfrontal meet- 

 ing an upward process from the jugal ; the 

 quadrate is large and immovable ; there 

 are large parotic processes ; the tympanic 

 cavity is completely bounded by bone ; the 

 teeth, which are borne by premaxillae, 

 maxillae, and dentaries, are lodged in dis- 

 tinct cavities; beside and eventually beneath 

 the teeth lie reserve " germs " of others. 



Each ramus of the mandible consists, 

 as in most Reptiles, of a cartilage bone — 

 the articular — working on the quadrate, and 

 five membrane bones — dentary, splenial, 

 coronoid, angular, and surangular. The hyoid region is very simple. 



The pectoral arch includes a dorsal scapula and a ventral coracoid 

 (with a characteristic foramen) ; there are no clavicles ; the sternum 

 remains cartilaginous ; the epicoracoids are thin strips between the 

 ventral ends of the coracoids and the front of the sternum ; there is an 

 episternum ; the fore-limb is well though not strongly developed ; 

 there are five digits, webbed and clawed. 



Fig. 420. — First vertebra 

 of crocodile. — From a 

 Specimen. 



The atlas here consists of four 

 distinct parts : (i) Pro- 

 atlas ; (2) lateral or neural 

 arch portion ; (3) ventral 

 or centrum portion ; (4) 

 first cervical rib. 



