374 ON THE PETKELS COLLECTED DUE1NG 



III. COMPABATIVE ANATOMY OF THE TuBINABES. 



My object in working out the present report has been, not to produce 

 a detailed description of the structure of any particular Petrel, but to 

 describe the most important deviations from the ordinary avian type 

 met with in this group, and to compare the members of it with each 

 other, and with other groups of birds, in those points of their structure 

 in which experience has shown birds to differ from each other. 



Some of the modifications here described are of great physiological and 

 morphological interest, whilst the numerous differences in points of 

 detail displayed in the different sections and genera of the Tubinares 

 lead one to expect that the future study of systematic ornithology will 

 be not a little elucidated by the labours of the anatomist, wherever he, 

 as in the present case, has material at his command sufficient for 

 something like an adequate study of a natural group on the basis of 

 structural differences more important than those that can be discerned 

 from the superficial inspection of an ordinary skin. 



In the present section the external characters, pterylosis, and visceral 

 anatomy are first described ; these are succeeded by an account of the 

 myology, to which follows a description of the tracheal structures, and 

 of certain other points in the anatomy of the soft parts. An account of 

 the osteology concludes the whole. 



1. External Characters and Pterylosis. 



There are some points in the external characters of the Tubinares that 

 may be noticed here, because in ordinary skins they can only be made out 

 with difficulty, owing to changes and distortion in the process of drying*. 



The order Tubiuares derives its name from the character, prevalent 

 throughout the group, of the external nares, which are prolonged into a 

 more or less lengthy cylindrical tube, lying usually on the dorsal surface 

 of the beak, and opening by one or two apertures (cf. figs. 1, 31, and 32, 

 infra, pp. 375 and 432). The exact disposition and degree of development 

 of these tubes vary in the different members of the group. 



In the Oceanitidae, and the smaller species of Procellariidae (belonging 



to the genera Procellaria, Cymochorea, and Halocyptena,}, the nasal tubes 



quite coalesce, lying on the dorsal surface of the beak for about its basal 



Zool. Chall. half ; the tube so formed rises rather abruptly from the forehead, and is 



Exp. vol. iv. truncated anteriorly, the single aperture so formed looking upwards and 



forward (vide PI. XII. figs. 1-3, PI. XIII. figs. 1-3). In the Oceanitidse 



(e. g. PI. XIII. fig. 5) the aperture viewed from in front is nearly circular, 



and with scarcely any appearance of a median septum. In the Procellarian 



* I need not do more here than refer to the peculiar bill of the Tubinares, the 

 peculiarity arising from the subdivision, into more or less distinct plates, of the 

 corneous covering of the mandibles, as it is sufficiently described in systematic works 

 on ornithology. 



