MONOGRAPH OF THE PETRELS. 



(" Challenger " Reports). No Petrel has a biceps slip, while the triceps itself is 

 somewhat degenerate. 



The muscles of the hind-limb vary much. The ambiens is absent only in 

 Fregetta, but in Garrodia and some others, it is degenerate, not crossing the knee. 

 All have a femoro-caudal, but its accessory head is absent in Bulweria and Pelecanoides. 

 The semitendinosus has an accessory head in Oceanites and its allies, but not in other 

 Petrels. The deep flexors blend about half way down the leg, but no slip is ever 

 given off therefrom to the hallux. 



Visceral Characters. 



The tongue shows degenerate tendencies, and a consequent considerable range of 

 variation in size, shape, and armature, e.g. in Puffinus brevicauda, Diomedea brachyura, 

 the dorsal aspect may be covered with small conical papillae, recalling those of the 

 Penguins, wherein these papilla? attain a relatively enormous size ; while in others, e.g. 

 (Estrelata lessoni and Majaqueus cequinoctialis, these papillae are limited to the lateral 

 border of the tongue. The inner border of the sheath of the upper jaw may bear 

 long horny lamellae, as in Prion, or be simply striated, as in Fulmarus. 



The proventriculus of the Petrels is enormous, while the gizzard is no less 

 remarkable on account of its small size, and peculiar shape and position. 



In the convolutions of the intestines, as Chalmers-Mitchell has demonstrated, the 

 Petrels display strongly marked peculiarities, in their nature akin to the convolutions 

 seen in the Divers, Penguins and Storks, and in no way resembling the type of 

 convolution which obtains among the Grues. 



Caeca are extremely reduced in all the Petrels ; in Oceanites and its allies, and in 

 Halocyptena they are absent. 



The Syrinx shows a wide range of variety in its structural characters, but 

 preserves an underlying resemblance to that of the Sphenisci and the Ciconiiform 

 types, and in no way approaches that of the Lari. 



Typically tracheo-bronchial, it has acquired in Pagodroma and Thallassoeca, for 

 example, the peculiarities of the bronchial type. But the various modifications which 

 this organ presents in the Petrels being of morphological, rather than taxonomic, 

 interest, the reader is referred to Forbes's Monograph for the detailed description 

 thereof. Suffice it to say that in some genera, notably in Fulmarus, Thalassoeca, and 

 Macronectes, the lower end of the trachea is divided by a median vertical septum, 

 dividing the lumen of the tube into right and left channels as in Penguins. In 

 Macronectes the specialization of the trachea from this point of view attains its 

 maximum, the lower end thereof being cleft to form right and left branches, each 

 continuous with its bronchus. Immediately distad of the cleft, the tube is for a short 

 distance divided by a median septum such as that just referred to, owing, apparently, 



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