Royal Society. 67 



the former is inserted into the third-digit slip of the long flexor 

 tendon ; the latter, or true accessorius, is attached to the front 

 of the two inner tendons, and is rather larger. The tendons 

 for the toes are thus coni}>lex in their mode of formation ; for 

 jdantaris and flexor digitorum, united with flexor hallucis and 

 the accessorii, form but one common series of tendons. The 

 flexors digitorum and hallucis first unite; these are joined by the 

 plantaris ; and the conjoined tendon receives the accessorii : 

 thus the outer-toe tendon is formed by the outer accessorius 

 and a slip from the common flexor; the inner receives the 

 principal body of the flexor hallucis and a slip of the others, 

 while the middle has one single tendon of composite origin. 



PEOCEEDINGS OF LEAENED SOCIETIES. 



EOYAL SOCIETY. 



Feb. 11, 1869.— Dr. W. B. Carpenter, Vice-President, in the Chair. 



" On the Structure and Development of the Skull of the Common 

 YoviX {Gallus domesticus}." By W. Kitchen Parker, F.R.S. 



In a former paper (Phil. Trans. 1866, vol. clvi. part 1, pp. 113— 

 183, plates 7-15) I described the structure and development of the 

 skull in the Ostrich tribe, and the structure of the adult skull of the 

 Tinamou — a bird which connects the Fowls with the Ostriches, but 

 which has an essentially struthious skull. 



That paper was given as the first of a proposed series, the sub- 

 sequent communications to be more special (treating of one species 

 at a time) and carrying the study of the development of the cranium 

 and face to much earlier stages than was practicable in the case of 

 the struthious birds. 



Several years ago Professor Huxley strongly advised me to con- 

 centrate my attention for some considerable time on the morphology 

 of the skull of the Common Fowl ; that excellent advice was at length 

 taken, and the paper now offered is the result. 



A full examination of the earlier conditions of the chick's skull 

 has cost me much anxious labour ; but my supply of embryonic 

 birds (througli the kindness of friends)* was very copious, and in 

 time the structure of the early conditions of the skull became mani- 

 fest to me. 



The earliest modifications undergone by the embryonic head are 

 not given in this paper : they are already well known to embryo- 

 logists ; and my })urpose is not to describe tlie general development 

 of the embryo, but merely the skeletal parts of the head. 



These parts are fairly differentiated from the other tissues on the 

 fourth day of incubation, when the head of the chick is a quarter 



* Dr. Murie is especially to be tlianked for his most painstaking kindness 

 in this respect. 



5* 



