14 ANATOMY 
condition live within such bags. Another imperfection of the 
ontogenetic record lies in the fact that the sequence in which the 
various organs are developed in the embryo does not always 
correspond with the temporary succession in which we know 
them to have been acquired during the phylogenetic develop- 
ment of the animal in question; thus feathers begin to bud while 
the skeleton of the embryo is still cartilaginous. Such discrep- 
ancies between the ontogenetic and phylogenetic development have 
been termed “ceenogenetic” by Prof. Heckel (from xaw,és, new). 
The fact of their frequent occurrence without our being aware of 
the various c4ses; warns us to be extremely careful in interpreting 
the various features exhibited by the embryo. In the present 
state of our knowledge it is often impossible to decide the taxonomic 
value of a given feature. 
Descriptive Anatomy requires a number of technical terms which 
shall not be ambiguous, or permit of doubt as to their intended 
meaning. For instance, terms like upper and lower, anterior and 
posterior, inner and outer, are often liable to be misunderstood. 
In ordinary parlance anterior corresponds with ventral in Man 
(with reference to whom many of our technical terms have been 
invented), but the head though at the anterior end of the animal 
is not ventral, and yet the anterior surface of a vertebra may mean 
its ventral surface. In fact, these vernacular names change their 
meaning according to the starting-point which happens to be 
used. 
It seems therefore advisable to enumerate, and give a definition 
of, those terms which it is useful to apply throughout in the 
description of the various organs of a Bird. 
The longitudinal axis of every bird corresponds with its vertebral 
column: one end is marked by the head, the other by the tail, thus 
giving the terms cephalic and caudal ; and concerning the neck, trunk, 
and tail, together with their constituent parts, anterior and posterior. 
On one side of the vertebral column or axis are situated the heart, 
lungs, and digestive organs ; this is the ventral, in opposition to the 
dorsal side. 'These give, combined with anterior and posterior, right 
and lef/. An axis at right angles with the longitudinal one, and at 
the same time running right and left, is a transverse axis ; beginning 
with the vertebral axis as the starting-point, the terms proximal and 
distal are applied to any organ or part which is referable to the 
longitudinal axis. These two terms are chiefly applicable to parts 
like ribs and limbs with their various elements. ‘The proximal end 
of the tibia articulates with the distal end of the femur; the 
proximal end of a rib articulates with a vertebra, and so on. The 
tip of the wing marks its distal, the AXILLA its proximal end. 
- With reference to an ideal plane through the longitudinal axis, 
and at right angles to the transverse axis, are applied the terms 
