26 PTERYLOGRAPHY. 



a. Long, that is to say extending from the extreme end of the iscliium to the knee. I t 



presents itself in this state in the genera Cypselm (Plate III, fig. 17), Trockilu s 

 (Plate III, fig. 19), Priorities, Musopliaga (s. Corythaix, Plate VI, fig. 9), Alcedo 

 (Plate VI, fig. 6), Upupa (Plate VI, fig. 4), and Psittacus (Plate V, figs. 17 

 and 18). 



b. Short, when it reaches neither the knee nor the pelvis. It has this form in some Owls, 



and in most of the Passerine birds (Plate III), and also in Galbula (Plate IV 

 fig. 8), Todus (Plate IV, fig. 10), Trogon (Plate IV, fig. 19), Scythrops, Micropogon 

 (Plate V, figs. 4 and 5), Bucco (Plate V, fig. 2), and Merops, and in the genera 

 Sterna and Rhynchops among the Loiigipennes. 



2. Like the preceding form, but the posterior end coalescent with the spinal tract. Examples 

 of this form are furnished by Lestris (catarrhactes, Plate IX, fig. 14), Procellaria (qlaciulis, 

 Plate IX, fig. 2), and Coracias (garndus, Plate IV, fig. C). 



3. Resembling the first form in direction, but so broad that it is connected with the spinal 

 tract even at its anterior extremity. I have found this rare arrangement in Cuculus (Plate IV, 

 fig. 12), and Puffinus (obscurus, Plate X, fig. 3), in which the tract is short, and in the Columla 

 (Plate VII, fig. 2), in which it is of considerable length. 



4. Long, straight, and united with the spinal tract both before and behind, so that an 

 apparently peculiar space is formed between them. I have seen this form only in Coitus (Plate 

 VI, fig. 11). 



5. Very broad and strong, so that it extends over almost the whole outside of the thigh, 

 but remains completely separate from both the spinal tract and the crural tract. Most Gallince 

 have a femoral tract of this kind (Plate VII), especially Phasianus, Gallus, Puvo, Tetrao, and 

 Perdix. 



6. Narrow but double, that is to say, divided into an outer and inner band, of which the 

 former is much more oblique and extends to the knee. I have found it in this form, in Strix 

 bracJiyolus, and the Toucans (Plate V, fig. 13). In the Woodpeckers, particularly Picus viridis 

 (Plate V, fig. 15), the two very short bands meet together behindhand the inner one consists 

 only of a single series of feathers. This is also the case with the Toucans. 



7. Sparsely feathered, clothing the whole outside of the thigh, and completely united with 

 the spinal tract. Examples are presented by the genera Diomedea (Plate X, fig. 4), Plolus 

 and Dysporus (Plate X, fig. 9) ; by several genera of Pygopodes, e. g., Colymbus (Plate X, fig. 11), 

 and by the genus Plicsnicopterus (Plate IX, fig. 7). 



8. I have found it to be entirely wanting in some rapacious birds (Plate II), such as 

 Gypaetos (fig. 2), Falco brackypterus (fig. 5), and Strix bubo (fig. 9), and in these cases the 

 crural tract is very strong. In other rapacious birds, a short band composed of a single series 

 of feathers occurs upon the hindmost part of the thigh, for instance, in Falco apivorus (fig. 4), and 

 Rhyncliodon peregrinus (fig. 6). The Veiled Owls (Hybris, such as H.Jlammea, fig. 10), alone 

 possess a strong, very oblique femoral tract, consisting of several rows of feathers. 



IV. THE VENTRAL TRACT (Pteryla gaslr&i) . 



This is usually simple at first, and only subsequently divides into a right and a left 



* 



