138 
MEMOIRS OF TEE QUEENSLAND MUSEUM. 
In the other type, the lateral cavity or pleuroccele forms a recess which 
is not expanded within the centrum ; the peripheral walls may be surprisingly 
thin, and most of the intramural space is filled with a complex of small 
laminar cavities. These laminae reinforce the thin peripheral walls, exhibiting an 
extraordinary combination of strength with relative lightness. The majority 
Text-figure 2. —Transverse section of dorsal vertebra of Ornithopsis (after J. W. Hulke). 
n. Neural canal, p. partition, 6. buttress, c. chamber, o.. o. lateral openings to 
chambers. 
of the small inner cavities appear to be more or less insulated, and there is 
no evidence of connecting passages between the lateral recess and this inner 
complex. This type of vertebrae is well illustrated in Diplodocus ccnnegii, as 
fully described by J. B. Hatcher (1901), who refers to the “remarkable degree 
of specialization, unsurpassed if not unequalled by other vertebrates in the 
general characters of its vertebral column in its adaptation of these mechanical 
principles which combine maximum strength with minimum weight (p. 12). 1 
It is very evident that the vertebrae of Austrosaurus mekillopi resemble 
those of Diplodocus in the special structure of the centrum. A transverse 
section of the centrum of Specimen A, shown in Text-figure 3, illustrates the 
proportions of the pleurocceles. taken at their maximum extent, and the intramural 
complex of cavities surrounding them. The recess behind the anterior lamina, 
above the centrum, is also indicated. 
A longitudinal section of a vertebra of Austrosaurus would exhibit a 
somewhat similar structure, but more complex, to that figured by Owen in 
his “ CJiondrosteosaurus ” from the Wealden deposits of the Isle of Wight. 2 
1 Hatcher, J. B., Mem. Carnegie Museum, Vol. 1, 1901, p. 12. 
2 Owen, R., Mon. Foss. Flop!. Wealden & Purbeck, Pal. Soc. Supp. VII, 1876, PI. V r 
n 
fig. 2. 
