The family Eurylaimidae differs in two important anatomical characters from the Pittidae. It differs from this latter family as from all other Indian families of the Passeres in having the flexor longus hallucis and the flexor profundus digitorum joined near the centre by a vinculum (fig. 85); the intrinsic muscles of the syrinx are attached to one pair only of the bronchial semi-rings instead of to two pairs as in the Pittidae.
The sternum is Passerine but has one notch on each side of the hinder border and the manubrium sterni or spina externa is unforked as in the non-Passerine birds. The oil-gland is present but nude.
The relations of this family to other groups has been dealt with in various ways by different Ornithologists but on the whole it seems advisable to retain them with the great Order of Passeres, even if it forms a somewhat aberrant family. In life their very close connection with the Passeres is obvious, and the most interesting discoveries of Dr. P. R. Lowe and Mr. G. L. Bates (P. Z. S. 1924, pp. 279-291) show how closely connected the Oriental Eurylaimidae are with the genus Smithornis, a genus of small African birds, hitherto generally retained in the family Muscicapidae. Pycraft had already called attention (P. Z. S. 1905) to the curious quadrate and other anatomical characters which influenced him in considering his Anisomyodi to be a branch or Sub-Order only, of the Passeres.
In this family the bill is normally very flat and broad. The feet are adapted for perching; hind toe large ; the anterior toes joined at' the base, the outer and middle toes (third and fourth) having only the last phalanx free (fig. 85). The tarsi, which are short but strong, are reticulated behind and transversely scutellated in front, the scutellation often ill-marked and in some genera entirely disappearing on the inner anterior side of the tarsus. The tail is generally rounded, often strongly, graduated.
Key to Genera.
A. Nostrils exposed.
a. Tail shorter than wing.
a1. Sides of upper mandible comex and overhanging.
a2. Region below eye feathered………..Eurylaimus, p. 461.
b2. Region below eye nude ………..Corydon, p. 464.
b1. Sides of upper mandible straight and not overhanging,
c2. Nostrils elongate and situated about one-third length of bill from forehead………..Cymbirhynchus, p. 466:.
d2. Nostrils rounded and situated close to base of bill………..Serilophus, p. 469.
b. Tail longer than wing………..Psarisomus, p. 472.
B. Nostrils concealed by loral plumes………..Calyptomena, p. 475.