DECEMBER 15, 1899. ] 
column. There is a balance of weight be- 
tween the dorsals and the anterior caudals. 
The laminar construction of the dorsals, 
sacrals, and caudals is shown to exhibit a 
unity of type, with local differences adjusted 
to special stresses and strains. 
REsTORATION AND Haspitrs or DipLopocus. 
We must await the discovery of the com- 
plete limbs and neck before Diplodocus can 
be wholly restored. Yet a number of 
important points regarding the general 
structure of the animal can be established 
now. The length of the entire skeleton 
was considerably greater than estimated by 
Marsh. The known and estimated linear 
measurements are as follows : 
. Meters. 
60+ 
3.65 
3.65 
61 
8.51 
The animal was about 60 feet in length 
and relatively more elevated and more slen- 
der than Brontosaurus. The proportions of 
the shafts of the femora, namely Diplodocus 
5, Brontosaurus 7, probably give us an ap- 
proximate idea of the weight ratio—that is, 
Diplodocus had about five-sevenths the bulk 
of Brontosaurus. 
We observe in Marsh’s restoration of 
Brontosawrus, a pioneer work of very great 
difficulty, that the mid-dorsal region is 
made the highest point in the backbone ; 
that the sacral region is subordinate; that 
the tail (in which 8 or 10 anterior caudals 
are now know to be omitted) is an appen- 
dage of the body instead of an important 
locomotor organ of the body. In all these 
points Marsh’s restoration is probably in- 
correct. 
We must consider therefore as three of the 
most important advances in our general 
knowledge of the structure of these animals ; 
first, the establishment of the sacral spines 
SCIENCE. 
873 
as the highest point in the backbone; sec- 
ond, of the sacrum and ilium as a center of 
power and motion; third, of the balance 
between the dorsals and caudals. 
Diplodocus gives us a new and different 
conception of the Cetiosaurs or Sauropoda, 
one which increases their ability as aquatic 
reptiles, and specializes the functions of 
the tail. The tail constitutes one-half 
the length of the animal, and was of im- 
mense service as a propeller in enabling it 
to swim rapidly through the water, the 
broad anterior portion being provided with 
very powerful lateral muscles, and the com- 
pressed posterior portion being controlled 
by tendons and made effective by a verti- 
eal fin. 
The tail, secondly, functioned as a lever 
to balance the weight of the dorsals, an- 
terior limbs, neck and head, and to raise 
the entire forward portion of the body up- 
wards. This power was certainly exerted 
while the animal was in the water, and 
possibly also while upon land. Thus the 
quadrupedal Dinosaurs occasionally as- 
sumed the position characteristic of the 
bipedal Dinosaurs—namely, a tripodal posi- 
tion, the body supported upon the hind feet 
and the tail. 
Thirdly, the supporting function of the pos- 
terior half of the tail is indicated by the 
sudden change in the shape of the chevrons 
at the 13th caudal; the chevrons of caudals 
13 to 19 indicate the region to which part 
of the main weight of the body was trans- 
mitted ; these chevrons are powerful and 
broadly spread out at the bottom. The 18th 
chevron is firmly anchylosed with the cen- 
trum; the 19th, 20th, 21st, 23d, 24th, 25th, 
are firmly connected with the centra by 
sutural surfaces, though not anchylosed. 
What may be termed the ‘ supporting and 
balancing’ tail of the Hadrosaurs, Iguano- 
donts and Megalosaurs is of a much simpler 
type than this ‘balancing, supporting and 
propelling’ tail of the Cetiosaurs. 
