REPORT ON THE ANATOMY OF THE PETRELS. 55 
scutes anteriorly. The claws are very flat, depressed, and lamellar. There are no colic 
ceca.* (Absent in Halocyptena only of the Procellariide.) There is a peculiar expansor 
secundariorum muscle. The tendon of the tensor patagii brevis is quite simple 
throughout. The semi-tendinosus muscle has a well-developed accessory head. The 
ambiens muscle, when present, does not pass over the knee, but is lost on the cnemial 
process of the tibia. The number of cervico-dorsal vertebrae is twenty-one. The 
clavicles have a long, curved, symphysial process. The leg bones are longer than the 
wing bones. ‘The tarsus is longer than the mid-toe* and ulna, and at least twice as long as 
the femur. The tibia is at least twice as long as the humerus, and much longer 
than the manus. The basal phalanx of the middle toe is as long as, or longer than, the 
next two taken together. 
The Oceanitidz also agree together in having no basipterygoid processes, no uncinate 
bone, a peculiarly short and stout humerus, radius, and ulna, a single circular nasal 
aperture, a sternum with its posterior margin quite or nearly entire, a larger gluteus 
primus, as well as in numerous other smaller details already noticed. All these 
characters never coexist together in any Procellarian form, and, if my observations are 
correct, the Oceanitidee further differ from the Procellariide by having a biceps brachii 
muscle of the normal form, with no patagial slip. 
The Procellaridze on the other hand, have the following characters :— 
The number of secondary remiges is never less than thirteen, and is usually much 
greater. The tarsi are pretty uniformly covered with small hexagonal scutelle. The claws 
are sharp, curved, compressed. Short colic caeca are present.’ There is no expansor 
secundariorum muscle. The termination of the tendon of the tensor patagii brevis 
is never quite simple, and may become very complicated. There is no accessory head 
to the semi-tendinosus. The ambiens muscle (only absent in Pelcanoides) always 
crosses the knee. The number of cervico-dorsal vertebra is not less than twenty-two. 
The clavicles have only a very small symphysial process. The leg is shorter than the 
wing. The tarsus is not larger than the mid-toe (except in Procellaria), and is shorter 
than the ulna. It is never twice as long as the femur. The tibia is only a little, or not 
at all, longer than the humerus or manus. The basal phalanx of the middle toe is shorter 
than the two next joints. Basipterygoid facets may or may not be present, and the 
same is true of the uncinate bone. The humerus, radius, and ulna have a shape different 
from that of the Oceanitide. The form of the nostrils, and of the posterior margin of the 
sternum, varies extensively. The gluteus primus is always very small, and there is a 
peculiarly formed patagial slip derived from the biceps muscle. 
1 Halocyptena is apparently an exception to this rule, but as Cymochorea has only one cxcum, there is nothing 
‘surprising in the reduction being carried a step further. As therefore all the congeners of Halocyptena have ceca, it 
may be safely assumed that their disappearance in it has been very recent, and has occurred since it acquired the 
rest of its Procellarian characters. This loss of caca therefore by it does not in any way really approximate it to the 
‘Oceanitide. 
