Sauropsida: Class Reptilia 



PL 



491 



Fig. 382. Skull of a crocodilian, Caiman latirostris, the irregularities of the 

 surface omitted, (an) Angulare; (art) articulare; (bo) basioccipital; (co) coronoid; 

 (d) dentale; (eo) exoccipital; (/) lacrimal: (mx) maxilla; (pf) postfrontal; (pi) 

 palatine; (pnix) premaxilla; (pt) pterygoid; (q) quadrate; (qj) quadratojugal; (sa) 

 surangular; (sq) squamosal; (tr) transversum; (z) zygomatic (jugal); (3, 5, 6, 9, 

 10, 12) foramens for exit of cranial nerves. (After Reynolds. Courtesy, kingsley: 

 "Comparative Anatomy of Vertebrates," Philadelphia, the Blakiston Company.) 



dermal bony plates. In some species bony plates occur both dorsally 

 and ventrally. Skull with quadrate bone firmly joined to adjacent 

 bones and all other bones of upper jaw immovably connected; right 

 and left rami of lower jaw firmly united in front (Fig. 382). Ribs (as 

 also in Sphenodon) have uncinate processes — a prong projecting 

 backward from one rib overlaps the rib next behind, thus tying the 

 ribs together (Fig. 363). Sternum well developed. Gastralia present. 

 Parietal organ not eyelike. Ventricle of heart completely divided 

 into right and left chambers. Cloacal aperture is a longitudinal slit. 

 No urinary bladder. Oviparous. 



The anatomic differences which distinguish the several members of 

 the Order are not important (Figs. 383, 384). Alligators have a broad 

 head with a blunt snout. In crocodiles the head is narrower and more 

 nearly triangular, and the snout is sharper. The heads of the several 

 species of caiman are intermediate in shape between heads of alligator 

 and crocodile. The gavial has an extremely long, narrow, and pointed 

 snout-region. 



Alligators are found in North America and (another species) in 

 China; crocodiles in tropical America, Africa, southern Asia, and 

 Australia; caimans in Central and South America; the gavial in 

 India and the Burmese region. The largest crocodilian is the gavial, 

 whose length may exceed 20 feet. Alligators and crocodiles range up 

 to 12 or 15 feet. Most caimans are smaller, but one species ("black 

 caiman") may attain 20 feet. 



