Hornhill Embryos and Nestlings. 545 



pygiclium) 386 ; upper mandible 61 ; lowei' mandible 73 ; 

 antebrachium 74; manus 57; tibia 98; tarso-metatarsus 

 68; hallux 21; 3rd digit 35, 



Stage 5. — Two advanced young of Anthracoceros malayanus, 



(Plate X.) 



These two young birds have so nearly assumed the general 

 appearance of the adult that I have but little to remark. The 

 upper mandible is very deep^ if measured across the nostril, 

 which is much further from the culmen than in Buceros 

 rhinoceros. The pygidiura is turned downward, and the 

 mouth of the cloaca is still very prominent. The foot is 

 exactly the same as in the adult : that is to say the ventral 

 scutes have appeared, one line of granular scales separating 

 them from the dorsal series. 



The pterylosis is interesting, inasmuch as not even yet 

 have all the feathers appeared through the skin. 



Pteryla capitis. — This is very much as in Stage 4, though 

 the feathers are naturally much longer. The posterior half 

 of the eye and the base of the mandible are naked. 



Pt. colli. — The back and sides of the neck are still quite 

 naked, but ventrally the tract is very well developed, occu- 

 pying the whole of the space between the rami of the 

 mandibles and running into the pt. ventralis. This very 

 late appearance of the lateral and ventral parts of the pt. 

 colli is interesting as being possibly evidence of a former but 

 now obsolete arrangement. In the adult the feathers on 

 these parts are small and ill-developed, while in Wiinoplax 

 vigil the whole neck is quite bare (^Dictionary of Birds' 

 Newton & Gadow, p. 434) ; whether or not this latter 

 arrangement is the more primitive it is not easy to say. 



Pt. spinalis. — The apterium of the neck extends down the 

 back as far as a point between the shoulders ; a very small 

 apterium in the adult persists at this point. The pt. spinalis 

 is perfectly continuous with the pt. humeralis, no apterium 

 separating them ; shortly before reaching the pygidium the 

 tract narrows down to a row of two feathers deep, and then 

 spreads over the pygidium, fusing with the coverts of the 



