REPORT ON THE ANATOMY OF THE PETRELS. 55 



scutes anteriorly. The claws are very flat, depressed, and lamellar. There are no colic 

 caeca.* (Absent in Ilalocyptena only of the Procellariidae.) There is a peculiar expansor 

 secundarioruni muscle. The tendon of the tensor patagii hrevis 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 Oceanitidae 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 Oceanitidae further differ from the Procellariidae by having a biceps brachii 

 muscle of the normal form, with no patagial slip. 



The Procellariidae 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 scutella?. The claws 

 are sharp, curved, compressed. Short colic caeca are present. 1 There is no expansor 

 secundarioruni muscle. The termination of the tendon of the tensor patagii hrevis 

 is never quite simple, and may become very complicated. There is no accessory head 

 to the semi-tendinosus. The ambiens muscle (only absent in Peleanoldes) always 

 crosses the knee. The number of cervico-dorsal vertebras 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 Oceanitidae. 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 caecum, there is nothing 

 surprising in the reduction being carried a step further. As therefore all the congeners of Halocyptcna have ea-ca, 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 ca;ca therefore by it does not in any way really approximate it to the 

 Oceanitidie. 



