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 
Fic. 76.--(a)—after Nitzsch~-Snipe, spinal feather tract divided ; (6) 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 ex¢ire or has notches or apertures ; what is the 
number of feathers in the tail. 
