268 CORVID/E. 



marked groups of Passeres, to which he has applied (Proc. 

 Zool. Soc. 1876, p. 507) the names Acromyodi and Meso- 

 myodi, according as the song-muscles (presently to he 

 described) are attached to the end or to the middle of the 

 incomplete rings forming the bronchial tubes. The latter 

 group, not being represented in the British Fauna, may be 

 here disregarded : the former group he separates into a 

 Normal and Abnormal division. This last contains no 

 British form, and therefore the Normal or true Passeres — 

 Oscines as they are termed by some — await our attention.* 



So far as structure goes there can be no doubt of these 

 normal Passeres forming an extremely homogeneous group, 

 perhaps one of the most homogeneous groups of the same 

 extent to be found in Nature. The more important 

 osteological features are common to all its members, and 

 means whereby the comparative anatomist may distinguish 

 the various sections into which convenience requires its 

 separation must be sought in modifications to which in 

 several Orders of Birds — to say nothing of other Classes of 

 Vertebrates — he would attach but slight value. And not 

 only is there this great uniformity in the skeleton, but, so 

 far as known, the arrangement of the vocal organs is 

 nearly identical throughout these true Passeres, while at 

 the same time it is unlike that found in any other group of 

 Birds. The bulk of the Raven renders it of all the British 

 members of the Order that in which these organs can be 

 most advantageously studied, and the figures of them here 

 introduced are given of the natural size, being copied, and 

 the description modified, from the Author's original memoir 

 (Trans. Linn. Soc. xvi. pp. 305-321, pis. 17, 18). f 



* The Editor desires to express his thanks to Prof. Garrod for his valuable 

 assistance in modifying the following account of the vocal organs of the Raven, 

 so as to adapt it to the present state of knowledge. The Editor however must 

 at the same time say that his friend's abnormal Passeres (the Australian genera 

 Menura and Atrichia) seem, from osteological characters, of greater significance 

 than those afforded by the voice-muscles, to be further removed from the true 

 Passeres than are many if not most of the Mesomyodi. 



f The excellent description and figures of the trachea of the Rook and other 

 birds, given by Macgillivray (Dr. B. ii. pp. 21 37, pis. x.-xii.), may also be 

 advantageously compared. 



