Embryos and Nestlings of Centropus sinensis. 657 
between itself and the pt. spinalis an elongate narrow 
apterium (see arrow in fig. 1 p. 655). At the knee the 
pt. femoralis runs into the— 
Pt. cruralis (fig. 2, pt. cr.) f which is divisible into two por¬ 
tions, a narrow pre-axial and a broader post-axial, which 
again are confluent with each other in the lower third 
of the crus on its outer aspect. 
Pt. colli lateralis (fig. 2, pt. coll, lat .) is at present well defined, 
though not recognizable in the adult or even in Stage 3 ; 
it branches off from the pt. spinalis at the junction of 
the head and neck, and runs obliquely on to the upper 
part of the breast, where it becomes confluent with the 
pt. ventralis. After its origin it is separated from the 
pt. spinalis by the apt. colli laterale, which runs down as 
far as the pt. humeralis (it is found also in the adult), 
and from its fellow of the opposite side by the naked 
skin of the throat. The trichoptiles of this and the 
following tract are very small. 
Pt. ventralis (fig. 2, p. 655, pt. v.). —This is, as yet, merely 
rudimentary, and the rudiments are curiously disposed. 
As is well known, the pt. ventralis in the genus Centropus , 
after bifurcating, redivides again on each side into an 
inner and outer branch. In the embryo now under 
discussion, the posterior end only of the inner branch is 
seen running on each side from the lower part of the 
stomach to the anus, and the upper part of the outer 
branch extends from its junction with the pt. colli 
lateralis to the level of the knee-joint only. 
The oil-gland is not tufted, and there is no pt. ani. 
Pt. caudae (fig. 1, pt.caud.). —The ten rectrices and their 
coverts are represented by short trichoptiles. 
Pt. alaris. —Owing to the small size of the fore-limb and the 
disproportionately long trichoptiles, it is almost impos¬ 
sible to make out their relative positions [cf. description 
of this tract in a nestling of Stage 2). 
With the exception of the pterylosis, there is not much in 
the external features of this embryo to call for special notice. 
The egg-tooth is small but prominent; the nostrils are 
