MOEPHOLOGT OF THE GALLINACE.E. 229 



Anterior. Posterior. 



Propodial bones. Humerus. Feniuv. 



Epipodial bones. Radius and ubia. Tibia and Fibula. 



Mesopodial bones. Carpals. Tarsals. 



Metapodial bones. Metacarpals. Metatarsals. 



Phalangeal bones. Finger-bones. Toe-bones. 



In the beginning of my work these researches were in their infancy, and the Bird 

 stood out from all other types as an anomalous form, deficient as to many elements of 

 the limb, and, on the liind limb especially, possessing only the ghost of a tarsal bone, and 

 that not in all cases ; this is a bone that serves as a sesamoid, but was thought to be 

 a rudimentary "calcaneal ossicle" (see Owen, Osteol. Catal. Mus. Coll. Sui-g. vol. i. 

 1853, p. 270, no. 1406). On page 258, no. 1355, the bone bad already been accurately 

 described as " a small cuneiform tarsal wedged into the outer and back part of the 

 ankle-joint." This great anatomist, however, only saw in this bone a rudimentary os 

 calcis, which it cannot be, being below that part. In all the Sauropsida the most 

 flexible part of the ankle-joint is not, as in Mammals, between the astragalus and 

 OS calcis (tibiale and fibulare) and the tibia, but between the astragalus and os calcis and 

 the distal part of the tarsus. Thus we have one of the many reasons for classifying 

 the Birds with the Reptiles ; and this once done (see Huxley, " On the Classification 

 of Birds," P. Z. S. 1867, pp. 415-472), a clear path was opened for fresh workers. 



For a long while the bilobate mass of separately ossifying cartilage at the end of the 

 tibia in a young bird had been an anomaly to me. In the year 1843 I dissected out 

 these parts in the chick of the Emu (six weeks old) and in young domestic fowls. 

 The drawings of these parts, still unptiblished and still unexplained, led me in 1860 

 {Balceniceps rex, T. Z. S. vol. iv. p. 343) to suggest very cautiously that that mass was not 

 an epiphysis of the tibia, but an astragalus. For I had then seen only one epiphysis in 

 the skeleton of a young bird, namely that on the cnemial process of the tibia *. 



But besides the bony separateness of the great upper tarsal mass in young birds, I had 

 seen a still earlier and greater distinctness, for the cartilage of this mass is distinct 

 from that of the tibia as well as the bone. Happily for science, this subject came 

 across the path of Professor Gegenbaur (see his Monoir in the Archiv fiir Anat. u. 

 Phys., Jahrgang 1863, pp. 450-472), and his researches were followed up by Professor 

 Huxley (see Proc. Zool. Soc. 1869, pp. 12-31, and also the paper just referred to in the 

 P. Z. S.) ; and uoav, at the present time, this subject has attracted a host of workers 

 and no little controversy. 



At the end of a full week of incubation, the leg, in my 1st stage (Plate XXII., and 

 Plate XXIII. fig. 1), has already taken on a tboroughly ornithoscelidan condition, and is 

 greatly modified from a normal ami^hibian or lacertian hind limb. Nevertheless, it 

 can be seen to be pentadactylc, and to have its sharpest line of segmentation between 

 the upper and lower series of tarsal segments ; also the fibula is not much shorter than 



* Within the last few years I have found a few more " epiphyses," namely, ou the top of the fibula iu Ujjtipa 

 epops, on the distal end of the radius in some small Passerines, and on the distal end of the ulna in Turdus meriila. 

 SECOND SERIES. — ZOOLOGY, VOL. V. 35 



