182 THE ANATOMY OF VERTEBRATED ANIMALS. 



-SB 



Fro. 68. — Diagram showing: the structure of the most important parts of tlie skeleton of 

 Ple-iiosaurvs. — A, the skull: J\^a, nasal aperture. — B, the left fore-limb : 77, humerus; 

 U, ulua: B. radius; r. i. u., radiale, intermedium, and ulnare, in the proximal row of 

 carpal bones; 1, 2, 8, distal carpal bones; iJ/c, raeticarpus; P/t, phalanges. — C, a dors^ 

 verlebra vnih ribs (Ii.\ and ventral ossifications v V.o). — D, the left hind-limb : ^, femur; 

 T, tibia; F. fibula; t. i.f., tibiale, intermedium, and fibulare, in tlie proximal row of tar- 

 sal bones ; 1, 2, 8, distal tarsal bones ; Mt, metatarsus ; PA, phal. nges. — E, the pectoral 

 arch; •^■r, scapula; Co, coracoid; a, clavicles and interclavicle (?).— F, the pelvic arcli; 

 /'&, pubis ; A ilium ; js, ischium. 



but there is a well-developed system of ossifications of the 

 wall of the abdomen, arranged in transverse rows from before 

 backward ; each row consists of a median bone, slightly bent 

 upon itself, thick in the middle, and thin at each end — and of 

 six other bones, three on each side, which are elongated and 



