230 FIELD COLUMBIAN MUSEUM. 
articulation unusually developed, centra of dorsal vertebre elongate: 
Genus Brachiosaurus. 
The type specimen of Brachitosaurus as now prepared for exhibi- 
tion, consists of the sacrum, seven presacral and two anterior caudal 
vertebre, the right humerus, coracoid, ilium, and femur, and a 
number of ribs more or less complete. It was collected by the 
Museum paleontological expedition of 1900 from the Grand River 
valley of western Colorado. (Pate LXXI.) When found, the verte- 
bral column was lying with spines downward and the vertebre were 
but little displaced from their normal relations. The ventral surface 
of the sacrum, the ilium, and the anterior caudal vertebrez were ex- 
posed, and had suffered more or less from weathering. 
At the seventh presacral vertebra the thin clay stratum in een 
the specimen was imbedded ‘pinched out,’’ and was replaced by a 
massive layer of sandstone with coarse sand and pebbles at the base. 
This, together with the uniform displacement of the ribs, humerus, 
and coracoid to the left and the presence of an isolated ilium of 
Diplodocus, which had the appearance of having been drifted up 
against the broken vertebral series, indicated that the anterior portion 
of the skeleton had been carried away by the invasion of a water- 
current after the specimen had been partially covered with sedi- 
ments. 
The humerus and coracoid were displaced some ten feet to the 
left, and when found the distal end of the former was exposed at the 
surface, broken and displaced. When the fragments had been gath- 
ered up and fitted to the portion still in the matrix the bone meas- 
ured almost seven feet in length. This length so much exceeded 
that of any humerus previously known, that the writer at the time 
believed it to be a crushed and distorted femur. Had it not been 
for the unusual size of the ribs found associated with it, the specimen 
would have been discarded as an Apatosaur, too poorly preserved to 
be of value. 
The conclusion that the bone in question was a distorted femur 
was given additional weight by the discovery soon after of a well- 
preserved femur of almost identical length, associated with the 
ilium and sacrum. But later, when the two leg bones were removed 
from the matrix and carefully compared in the laboratory, the iden- 
tity of the humerus was at once established by the structure of the 
head as well as by the clearly defined deltoid area from which the 
deltoid crest had been broken away and lost. From figures 3 and 4, 
Plate LXXIV, the characteristic structure of the opisthoccelian 
humerus will at once be recognized. 
