14 ANATOMY 



condition live Avitliin 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 Ave know 

 them to haA'^e 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 " caenogenetic " by Prof. Hseckel (from /catvo?, new). 

 The fact of their frequent occurrence without our being aware of 

 U^/ the various cases, warns us to be extremely careful iu interpreting 

 the various features exhibited by the embrj'o. 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 Avith 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 hajDpens 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 Avith 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 giA^e, combined Avith anterior and posteiior, right 

 and left. An axis at right angles with the longitudinal one, and at 

 the same time running right and left, is a transverse axis ; beginning 

 AAath the vertebral axis as the starting-point, the terms 2)roximal and 

 distal are applied to any organ or part which is referable to the 

 longitudinal axis. These tAvo terms are chiefly applicable to parts 

 like ribs and limbs Avith their A'arious elements. The proximal end 

 of the tibia articulates Avith the distal end of the femur ; the 

 proximal end of a rib articulates with a vertebra, and so on. The 

 tip of the Av^ing 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 



