OF THE HEAD, WING, CRURAL, AND CAUDAL TRACTS. 31 



clature may certainly give the name of tracts to these portions of the plumage also, and in this 

 case the following must be added to those already mentioned. 



VI. THE HEAD-TRACT (Pteryla capitis). 



This usually clothes all the regions of the head, and passes over directly into the spinal and 

 ventral tracts, so that these, as it were, originate from it ; but if the lateral neck-space be only 

 visible lower down on the neck, the head-tract may also be regarded as continued on the 

 neck. 



VII. THE WING-TRACT (Pteryla alaris). 



This is double, one for each wing ; it comprises all the feathers inserted upon the wing, with 

 the exception only of those which form the humeral tract. To this tract, therefore, belong the wing- 

 feathers (rcmigcs) inserted into the hinder margin of the whole wing, from the finger-tips to the 

 elbow ; the arm-feathers (ptcromatci), which run down the inner surface of the lower arm in from 

 one to three series ; i\\G feathers of the wing-coverts (tcctrices), or the feathers of the upper side of the 

 wing-membrane and of the upper surface of the arm ; the bastard winy (alula spuria) inserted upon 

 the thumb, and also the upper and lower accessory wings (parapterum superius et inferius, or, as I 

 call them, the parapterum and kgpoptervm), 1 of which the one is usually inserted at the hinder 

 margin of the upper arm, and the other on its inner surface. The wing-tract further includes 

 the plumage of the great wing-membrane, especially the portion inserted on its margin, which 

 is separated from the rest of the plumage by the upper and lower wing-spaces, and usually passes at 

 the shoulder into the ventral and axillary tracts. 



VIII. THE CRURAL TRACT (Pteryla crumlis). 



This tract is also double, and occurs of the same form on both the right and left legs. It 

 clothes the whole or the greater part of their surface, and extends, in some birds, also over the 

 tarsus, and in a very few even to the toes. It is often weak throughout, or at least on the inside 

 of the leg ; on the outside, however, it is very strong in some birds, especially in all the diurnal 

 birds of prey, and in the true Cuckoos (Cuculus). It will be more particularly described when 

 the crural space comes under notice. 



IX. THE CAUDAL TRACT (Pteryla caudalis). 



This occurs on the true tail, or the last caudal vertebrae. From it originate the rectrices, 



MOHRING named these accessory wings (which ILLIGER singularly confounded with the axillary 

 feathers) alee nothce. The lower accessory wing is, however, composed of a series of flat feathers which 

 runs along the inner side of the upper arm, not unfrequently as far as the breast, or even issues from 

 the lateral branch of the ventral tract. It covers the lower wiug-space, or, when longer, even a great 

 part of the lateral space of the trunk. 



