THE GENERAL SUBJECT* 
Aves 15 
Special, contains 837 pages, and is devoted to a minute description of the 
bones, nerves, and muscles of the Bird’s shoulder-girdle— the result of the 
examination of many hundreds of specimens of all kinds. In the second 
and more General part, the author remarks that the study of the 
morphology of Aves well repays the labour, not because the Class 
exhibits any great or fundamental variety, but because in it several 
organic systems reach a height not elsewhere attained — small groups of 
Birds often presenting much differentiation of organs, and thereby render- 
ing it possible to judge of the significance of the respective differences. 
The origin and development of particular structures, the formation of 
joints, the nature of sesamoid bodies, the connection of muscles with the 
nervous system, their variability, and the shifting of the limbs along 
the vertebral column are discussed from a very general point of view ; 
and this last (the retrogression of the limbs) is shewn to have reached 
its highest degree in Birds, and especially in large Birds. The same con- 
sideration applies, as might be expected, to the muscles which move the 
limbs, and the Ncubildung (an untranslatable word in this sense) is 
attempted to bo explained. Passing to more particular topics, the 
author remarks that small Birds show more primitive and simpler con- 
ditions of structure than their larger allies. The first Birds were probably 
smaller than Arcliceopteryx , and the study of the smaller members within 
given groups promises to throw the most light on their phylogeny. In 
the second part of the second volume the taxonomic value of the various 
characters of all the organic systems is criticized, and a selection of 48 of 
them, not, of course, of equal value, as presented by the 90 families into 
which the class is divided, is tabulated. The result shews that those 
offered by the bill, feet, and oil-gland are comparatively worthless, while 
pterylosis is never to be neglected. Then follows a disquisition on 
oology, after which osteological characters are considered, especially in 
regard to the discovery of a unit for measurement, on the existence of 
which the author’s labour seems to throw doubt. The anterior portion 
of the sternum is shewn to be noteworthy ; but more important still is 
the maxillo-palatal structure, though Huxley’s taxonomy based on this 
[cf. Zool. Rec. iii, pp. 46-49] seems to be artificial, as the numerous 
exceptions, ascertained by later researches, go to prove. In some cases 
the hyoid bones afford good characters. The extent of the coraco-scapular 
angle depends inversely on the development of the humeral muscles, as is 
shewn in a tabular form. The difficulty of determining the homologies 
of the constituents of the pelvis is then considered, but with unsatis- 
factory results, though the subject is evidently one of promise. Here 
there is no space for more than allusion to the chapters treating of 
Palaeontology and Geographical Distribution ; but a peculiarly important 
feature of this work is to be found in the two plates giving lateral views 
of the supposed ancestral tree of the Class, and three others representing 
&s many sections through this ideal tree at different epochs. The Classi- 
fication adopted as the result of all this unparalleled labour is shewn in 
the following scheme, reduced to the minimum of detail ; and cannot 
but compare favourably with other plans that it has been the duty of 
the Recorder of Aves to set forth from time to time 
