C. B. TICEHURST: DOWN-PLUMAGE. 



187 



pass backwards, each tract forming, in most species, a line 

 or crescent of down. It will be noticed that the inner supra- 

 orbital tracts are present in every species which I have 

 examined which has down at all. 



The outer supra-orbital tracts consist of two or three small, 

 short pre-pennse on each side, situated between the edge of 

 the upper eyelid and the inner supra-orbital tract. They are 

 present in the Mistle-Thrush, Meadow and Red- throated 

 Pipits, Chaflfinch, and Brambling. 



The occipital tracts consist of two or three fairly large, 

 well-developed, pre-pennse situated on each side of the occiput. 



Outer 



supraorbital. 



tract 



Crural 

 tract 



Ventral 

 tract 



Crural 

 tract 



Diagram showing the Down-tracts of Nestling Birds. 



The two tracts usually form a line, or crescent, of down when 

 well developed. They are present in every species examined 

 which has any down. 



The humeral tracts are usually well developed, and run 

 obHquely downwards and outwards from the base of the neck 

 across each humerus just in front of the shoulder joint. They 

 are replaced by the " scapular " feathers of the juvenile 

 plumage. They are present in all the birds that I have 

 examined which have down, except the Wren (see note under 

 this species). 



The spinal tract runs down the centre of the dorsum from 

 about the level of the shoulder joint to the end of the sacrum 

 in those species in which it is well developed. The length 



