384 THE STRUCTURE AND LIFE OF BIRDS chap. 



present ; the relation of the branched tendon that 

 flexes the toes to that which flexes the hallux (see 

 p. 167) ; the presence or absence of the ambiens muscle 

 (see p. 169) which passes from the pelvis to the toes ; 

 the distribution of the feathers on the neck and back 

 — whether there is a clearly defined tract of feathers 

 on the neck with bare spaces or apteria on either side, 

 and whether this tract forks, an apterion dividing it 



Fig. 76. — (a) — after Nitzsch— Snipe, spinal feather tract divided ; (b) Black- 

 bird, tract undivided. 



into two arms, when it reaches the back ; whether 

 there is an oil gland at the root of the tail, and whether 

 this, if present, is bare or tufted with feathers ; whether 

 the young are helpless when born, whether they are 

 born naked or covered with down, and, if naked, 

 whether they pass through a down-stage before their 

 feathers grow ; whether the hinder part of the ster- 

 num is entire or has notches or apertures ; what is the 

 number of feathers in the tail. 



