Embryos and Nestlings o/Centropus sinensis. 663 
(fig. J), except by means of the still persistent tricho- 
ptiles, but originates at a point about midway between 
the mid-dorsal line and the articulation of the humerus,, 
from here it runs up to and over the point of the 
shoulder to fuse with the pt. ventralis; it is also con¬ 
tinuous with the tectrices marginales but not with the 
parapteron. The sheaths, which are long and still pro¬ 
vided with trichoptiles, are arranged in three rows deep. 
The distance between this tract and the following is 
much greater than formerly. 
Pt. femoralis (fig. 4, pt /.).—A glance at the diagram will 
show the peculiar nature of the tract at this stage : it is 
plainly divisible into two portions, a pre-axial and a 
post-axial; the former is rather indistinct, arising from 
the pt. spinalis it runs obliquely upwards for a very 
short distance; the latter is not connected with the 
spinal tract, its base-line is of considerable length, the 
lower extremity sweeping down past the pygidium and 
not far separated from the lower extremity of the inner 
branch of the pt. ventralis; from this base-line the 
feather-sheaths rapidly converge and run over the out¬ 
side of the thigh, mostly on its post-axial half. The 
greater extent of this tract in younger stages is shown 
by the triclioptiles. 
Pt. cruralis has not altered in shape or size, though its 
pre-axial portion has lost its connection with the 
pt. femoralis owing to the reduction of that tract. 
Pt. ventralis (fig. 5, p. 661,pt. v.). —This is now well developed 
and dense. Commencing as a continuous tract between 
the mandibular rami (cf. ante), it divides at the junction 
of the head and neck into two broad main stems; these run 
down the sides of the neck and chest for some distance, 
when each stem re-divides into two branches—an outer, 
short branch *, so short, in fact, that it hardly appears 
to be a branch at all; and an inner, narrow branch, which 
runs down almost to the level of the anus, diverging 
slightly from its fellow on the opposite side. The 
* This branch is said to be very short in Rkinococcyx. 
