REPORT ON THE ANATOMY OF THE TETRELS. 11 



MM. Grandidier and A. Milne-Edwards have given figures of the skeletons and separate 

 bones of Prion vittatus, Pitffinus chlororhynchus, and Thalassidroma oceanica. 



III. COMPARATIVE ANATOMY OF THE TUBINARES. 



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 adecmate study of a natural group on the basis of structural differences more im- 

 portant 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 descrip- 

 tion 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. 1 



The order Tubinares 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, 32, and 33, infra, pp. 12 and 59). 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 Procellariidse (belonging to the genera 

 Procellaria, Cymochorea, and Ilalocyptena), the nasal tubes rpuite coalesce, lying on the 

 dorsal surface of the beak for about its basal half; tin- tube so formed rises rather 



1 I need not do more here than refer to the peculiar hill of the Tubinares, — the peculiarity arising from the sub- 

 division, into more or less distinct plates, of the corneous covering of the mandibles, — as it is sufficiently described in 

 systematic works on ornithology. 



