OF THE VENTRAL TRACT. 27 



portion. It alone constitutes the plumage over the whole inferior region of the body to which 

 llliger has given the technical name of gastraum, and it commences at a greater or less distance 

 from the angle of the throat, except when it is connected with the uniform plumage of the head 

 and nape by means of the throat-feathers. It is separated from the other tracts by the lateral 

 spaces of the neck and trunk, and in proportion as the neck-space ascends towards the head, 

 so does the ventral tract commence nearer to the head or throat. Usually, however, it commences 

 at the chin, as in the nocturnal birds of prey (Plate II), or it, at least, originates at the angle of 

 the throat, and is undivided through its first and shorter portion, but is soon divided, by the intru- 

 sion of the ventral space, into a right and a left band, which pass separately and uninterruptedly 

 upon the breast, 1 after receiving the humeral tracts, or a lateral lobe of the plumage of the 

 great wing-membrane ; they are then continued along the belly and extend as far as the anus, 

 or the tail. On the breast, each band generally emits an external lateral branch ; and in very 

 rare instances there is a second but earlier branch running inwards to the furcula, as in Galbula 

 (Plate IV, fig. 7). We may, therefore, readily distinguish three parts in the ventral tract, 

 namely 1, the yular portion (Kehtthcil) which is situated on the neck; 2, the truncal portion 

 (Ptcryla thoraco-ffastricd) which extends over the breast and belly ; and 3, the branch, or 

 external offshoot, which I sometimes call the lateral tract (Pteryla lateralis), and which is situated 

 on the side of the breast, beside the truncal portion, and gives origin to those feathers, usually 

 of large size, and often standing very close together, upon which the folded wings rest. Lastly, 

 the inner branch, when it occurs, originates from the lower -extremity of the gular portion, and 

 is always quite short. 



In different groups of birds the ventral tract presents differences as great and as deserving 

 of notice as those of the spinal tract. These differences relate to the width, to the closeness of 

 the plumage ; and to the direction and form of the tract. The arrangement of the branches is 

 particularly variable; sometimes they may be distinguished clearly enough, from their well- 

 marked separation from the truncal portion ; but sometimes they are united with the latter, and 

 have only the extremities free. At the same time, they are sometimes long, sometimes short ; 

 sometimes broader than the truncal portion, sometimes equal to it in width, and sometimes nar- 

 rower. In form, I have seen it lanceolate and pointed, and also truncated or rounded at the apex. 

 In some birds, as, for example, the genera Coracias, Bamphastus (Plate V, fig. 12) and Strix 

 (Plate II, fig. S), and in the Falcons, it is of a hook-like form, emitting a linear band extending 

 from the hepatic region to the humerus. This line seems to pass over upon the inner wing- 

 membrane, into the false winy (ala notlid) described by MOIIRING. In a few birds the branch 

 returns posteriorly into the truncal portion again, thus forming an insular space, which is com- 

 pletely surrounded by the ventral tract (e. y., in Centropus, Plate IV, fig. 13). The branch is, 

 however, deficient in many birds, and when this is the case the truncal portion becomes dilated 

 upon the breast ; its outer margin may then remain quite straight without any indication of an 

 angle or lateral projection ; or, it may be suddenly narrowed at an obtuse angle at the region 

 where the knee lies, to which I give the name of the knee-covert (latibulum yeniculi seu cruris). 

 Such a dilatation of the tract is to be regarded as essentially analogous to a branch which has 

 not been separated, but is combined with the main tract throughout its whole length. The 

 ventral tract is almost always continuous ; I have rarely met with a false (e.y, in Nyctornisyrandis, 



1 I give the name of the breast to the whole region of the body that lies over the sternum. 



