22 PTERYLOGRAPHY. 



retains the same breadth throughout its entire course. Most frequently it is widened in one of 

 two places, namely, either between the shoulders or behind them on the back, or in both spots, 

 afterwards becoming narrow again. There are, however, some birds in which it is much broader on 

 the whole of the back than on the neck. It is sometimes continuous, and sometimes has real or false 

 gaps. These gaps likewise usually occur at two spots, near the above-mentioned widened portions, 

 namely, either at the boundary of the free and covered portions, which is most frequently the case, 

 or further down on the back. The spinal tract in such cases usually appears very broad, densely 

 feathered, and strong, immediately before the gap ; whilst behind it is weakened, and only gradually 

 acquires stronger feathers. Moreover, the spinal tract is often divided, and then contains a 

 spinal space, varying in length and breadth, at the point where otherwise the widening usually 

 occurs. Sometimes, and this is very singular, a row of distant feathers accompanies the sides of 

 the hindmost part of the tract, as I find to be the case in the Woodpeckers (Plate V, fig. 15). 

 The different forms which I have observed in the spinal tract are as follows : 



1. Continuous throughout its course and strong, without any perceptible dilatation or 

 division, as in Priorities momota and Epimaclius superbm ; this form is, however, distinguishable 

 with difficulty from a similar tract interrupted by a false gap. 



2. Continuous along the whole back, and scarcely perceptibly widened in the middle, but 

 weak and somewhat stunted at the nape, as in some species of Alcedo, especially A. ispida. 



3. Like the preceding, but strong at the nape, and interrupted between the shoulder-blades 

 by a false or real gap, which is either broad or narrow. Examples of this form are furnished by 

 Alcedo rudis, A. maxima, and A. capensis. In Dacelo gigantea the whole dorsal portion is weak, 

 whilst the cervical portion is strong. 



4. Continuous and strong, narrow almost throughout, but widened on the back into a shield 

 or saddle, usually rhombic (rarely elliptical or roundish) in form, and then again narrow. This 

 form of spinal tract occurs in nearly all those passerine birds which do not exhibit the fifth form ; 

 I have also seen it in one genus of Cuculints, namely Trogon. Sometimes the portion before the 

 saddle is broader than that behind it, sometimes the reverse is the case. In Oriolus (Plate III, 

 fig. 8) and Pardalotus the dilatation is more elliptical, as also in Trogon viridis ; in Trogon 

 glocitans, on the contrary, it is rhombic (Plate IV, fig. 19). 



5. Exceedingly similar to the preceding form, but the partially-covered rhombic saddle 

 encloses an insular lanceolate or rhombic space. I have met with a spinal tract of this kind in 

 the passerine genera Corvus, Ampelis, Coracina, Eurylaimus (E. nasutus, Plate III, fig. 15), 

 Chasmorhynchus, Psaris, Ptilorhynchus, Cephalopterus (Plate III, fig. 10), Sericulus, Glaucopis 

 (G. varians), Pipra, Orinus NOB. (Rupicola AUCTT.), Phibalura, Alauda, Dic&um, Edolius, Oxyrliyn- 

 chus, Tyrannus, and Arachnotheres ; and also in the Cuculine genus Prodotes (Indicator AUCTT., 

 Plate IV, fig. 17). 



G. Agreeing with the fifth form, but the dilated portion, which is situated very far back, is 

 interrupted once or twice, and thus becomes bilobed. A tract of this kind occurs in Picus, in 

 which there are two gaps, one before the other at the posterior extremity of the bilobed saddle 

 (Plate V, fig. 15), in Yunx, Bucco (armillaris, Plate V, fig. 2), Pogonias (sukirostris) , in which the 

 arms of the furcate saddle are united to the posterior portion of the tract by a row of distant 

 feathers (Plate V, fig. 7), and in Micropogon (erythropygos) , in which the gap is exactly in the 

 middle of the saddle (Plate V, fig. 5). Lastly, this form also occurs in the passerine genera 

 Hirundo (Plate III, fig. 14) and Dicceum. It readily passes into the preceding form when the 



