On THE OSTEOLOGY OF NYCTOSAURUS. 137 
ures about 75 mm. in length, 2 across its somewhat expanded head, .8 
across the shaft a little beyond the capitular thickening, and but .4 near its 
distal extremity. The sixth vertebra has its rib on the left side in relation 
with the extremity of the diapophysis; it is a little shorter, .75 in width 
near its proximal extremity, and .3 distally. The seventh also has a rib in 
relation with the left diaphophysis; it is yet shorter, and nearly straight; 
measures .6 in width proximally, and .2 distally. The next rib is straight, 
and yet more slender, and shorter. The tenth vertebra, that connected 
with the sacrum, I do not think bore a free rib. 
In a former paper I stated my belief that the slender, posterior, single- 
headed ribs did not inclose the abdominal cavity, but were directed more 
or less outwardly in the patagial membrane. In support of this belief it 
is seen that all these ribs are remarkably slender, and but slightly if at all 
curved. Their free and loose connection with the vertebra, and their 
delicacy prevented them from being of use as a support to the abdominal 
contents; certainly not if the animal walked in a quadrupedal position. 
Furthermore, if they extended in the walls of the abdomen, the abdomen 
must have been exceedingly voluminous, and widely unprotected in front. 
A better support for my contention is afforded by the position of the 
various bones in this specimen as they are preserved. All these ribs lie 
directed outwardly or obliquely backward, and none of them are mutilated 
or broken in the least, save as may have happened in the preparation of 
the specimen. The right arm lies obliquely across the abdomen; it was 
evidently sustained by the soft parts until after the ligaments connecting 
the forearm bones had partly decomposed, since these two bones and the 
carpals only are slightly disassociated from the remainder of the wing 
bones. The radius and ulna fell to the back part of the abdominal 
cavity while yet the pelvis was held together, permitting the left innomi- 
nate bone to fall outward over the end of the ulna and carpal. Further- 
more, the ventral ribs have fallen upon the radius. Now, under these 
conditions, had the ribs curved forward in the abdominal walls to meet 
the ventral ribs, they surely would have been entangled and doubled up 
beneath the forearm. But this is not at all the case, and it seems highly 
improbable that the fleshy walls of the abdomen could have fallen apart, 
and spread out laterally with the wing folded across them. From all of 
which evidence, I believe that the ribs were directed laterally, supporting 
the patagial membrane, perhaps as in Draco, and that nes did not inclose 
the abdominal cavity. 
Further evidence of the same tenor is furnished by the type specimen 
of Rhamphorhynchus phyllurus Marsh, which I have recently examined. 
In this specimen, the right arm had also fallen across the abdomen, while 
yet having the patagial membrane attached to it. Nevertheless, the very 
