656 
Mr. R. Slielford on the Pterylosis of the 
the embryo; being all directed backwards they constitute a 
regular flowing mane (Plate XIII. A), the exact boundaries 
of which are not easy to define. None of the actual defini¬ 
tive feathers have yet made their appearance, so that the 
following description applies strictly to the distribution of 
the trichoptiles. 
Pt. capitis (fig. 1 *, p. 655, pt. cap .).—This is very well 
developed on the crown and back of the head, but is 
sparse on the sides; the skin below the ear, between 
the mandibular rami and between the eye and nostril is 
naked, a few delicate threads are to be seen surrounding 
the upper and posterior borders of the ear-opening and 
on the gonys of the mandible. The eyelashes have not 
yet made their appearance. 
Pt. spinalis (fig. 1, pt. sp.) is confluent with the pt. capitis; 
at first it is single, but at about the level of the attach¬ 
ment of the humerus it bifurcates, the two branches 
again reunite in the lower lumbar region and run on to 
the pygidium, stopping short just in front of the oil- 
gland papilla. The apterium between these two spinal 
branches is very narrow, and might easily be overlooked 
had one no later stages at hand for comparison. 
Pt. humeralis (fig. 1 ,pt. hum.) arises from the pt. spinalis just 
below the point where the bifurcation begins, and runs up 
to the point of the shoulder to fuse with the trichoptiles 
on the patagial membrane; its connection with the pt. 
ventralis is not yet established, nor does the ill-developed 
parapteron join it. 
Pt. femoralis (fig. 1, pt.f.) is a triangular tract, the long 
trichoptiles converging from the back over the whole of 
the outside of the thigh to a point at the knee; anteriorly 
the base of this triangle is confluent with the pt. spinalis 
for a short distance, but it soon diverges and runs down 
as far as the anterior angle of the pygidium, leaving 
* The figure representing Stage 2 is introduced here for expediency, 
since the difference between it and Stage 1 is almost imperceptible 
(see p. 658). 
