1896. ] ANATOMY OF RIYNCHOPS. 301 
Rhynchops shows a peculiar feature of Larus argentatus (¢f. fig. 2) 
and of most Auks in the existence of these patagial tendons (A) 
on the ulnar side of the arm. In Rhynchops there are two instead 
of only one of these ; they run side by side obliquely, or really at 
right angles to the longus tendon when the wing is extended, and 
end upon the extensor metacarpi radials muscle, on the inner side 
of the forearm ; the posterior of the two is inserted at a point 
Patagial tendons of Larus argentatus (after a MS. sketch by the late 
W. A. Forbes). 
m, osseous nodule. Other lettering as in fig. 1. 
almost exactly corresponding with the insertion of the wristward 
slip of the brevis, though, as already said, on the opposite side of 
the arm. On the opposite wing I could find only a single tendon ; 
it was, however, very much longer, reaching further over the arm. 
The pectoralis muscle sends a slip to the patagial tendons, which is 
slightly differentiated from the rest of the pectoralis as a muscular 
belly ; there is also a yellowish fibroid slip from the deltoid crest of 
the humerus. 
I could detect no biceps slip to the patagium on either wing. I 
looked, of course, very carefully for this muscle, as it is present in 
all the immediate allies of Rhynchops. 
The biceps is a very slender muscle which arises from the 
coracoid only. I found no trace of the missing humeral head. 
The muscle is divisible into two halves, the division commencing 
early in the slender tendon of origin. ‘The outer of the two 
