Ichthyosauria. 
33 
the flat surfaces on the centra. Intercentra are present between 
me sk uli and atlas, and between the atlas and axis. The dorsal 
ri s aie double-headed. Ribs are present in the caudal region ; 
the chevrons are not united below. Abdominal ribs are present, 
hut there is no sternum. There are clavicles and a T-shaped 
interclavicle present in the pectoral girdle; the coracoids do 
not overlap, there is no distinct precoracoid. The pelvis is 
Wall-case, 
No. 14. 
Table-cases, 
Nos. 13, 14. 
lio. 41. Left lateral aspect of skull of Ichthyosaurus latifrons (Kiinig), from the 
Lower Lias of Barrow-on-Soar, Leicestershire, i- nat. size. 
weak, the iliac bones are not connected with the vertebrae, there 
is an open obturator notch. The skull had very larg*e orbits, 
and the eyes were surrounded by a ring of broad bony 
(sclerotic) plates. The jaws were elongated, and armed with 
powerful teeth implanted in g'rooves. The hand and foot are 
modified into fin-like organs, composed of short polygonal bones, 
arranged in five closely approximated rows, with supernumerary 
rows of marginal ossicles added (see Figs. 45 and 46). 
Fig. 42.— A, superior, and B, right lateral aspect of the skull of Ichthyosaurus Zetland - 
icus (Seeley) from the Dpper Lias of Normandy (reduced). Pmx, premaxilla ; Mx 
maxilla; N, nares; Na, nasal; Fr, frontal; Prf , prefrontal; Ptf, postfrontal ; Pa, 
parietal; J, jugal; QvJ quadratojugal; Sq, squamosal; St. supratemporal ; For, 
postorbital ; A, orbit; B, supratemporal fossa; Set, sclerotic; Md, mandible; 
dentary; op, splenial ; ang, angular; k, articular (after Zittel). 
The largest entire Ichthyosaurus is from Lyme Regis, and 
measures 22 feet in length and 8 feet across the expanded 
paddles; but detached heads and parts of skeletons prove that 
they often attained a far larger size than this. 
(1189) 
4 
