li'Ol.] AXATOMY or Guuiron.M BTuns. (55-3 



Gastrocnemius. — Apart from the middle or posterior femoral 

 head, which I have discussed above in couuection witli the femoral 

 insei'tion of the cand-ilio-flexorius, the archecentric condition of 

 the gastrocnemius in birds appears to be the existence of a strong- 

 anterior femoral head, \vith which the short arm of the biceps- 

 sling is connected, and a very strong tibial (inner) head, the 

 tendons from the two heads uniting and running down to the 

 ankle-capsule. The anterior femoral head is double in Gariama, 

 there being, in addition to the normal head to which the biceps- 

 sling is attached and Mhich lies uuder the separate deep slip of the 

 femori-tibialis, a head passing external to that muscle. In Otis 

 both these heads ai-e present, and there is a third head to which 

 the biceps is superficial. In Enri/jn/c/a there are three heads with 

 similar relations. In Heliomis the anterior femoral head is 

 enormous, but I found no trace into the two or three divisions 

 found respectively in Canama and Otis. 



The middle and outer heads of the gastrocnemius show marked 

 variations amongst the Gruiformes, but these do not present an\- 

 definite correlation with the apocentric and archecentric conditions 

 of the wing. 



Solevs. — This muscle is present in all, and has the origin (text- 

 figs. 81, 82, 83, S-I, SOL.) normal in birds ; its tendon passes down 

 to the ankle-capsule without fusing with that of the gastrocnemius. 



FJexores lyerforantes et perforati. — The superficial flexors of 

 digits ii. and iii. are present in all the Gruiformes and have the 

 relations normal in birds. In Balearica the tendon for the second 

 digit fuses with the tendon of the perforated flexor of the same 

 digit for some distance along the tarsus, but the two separate 

 before insertion. Except in Psojjhia ohscura and Heliomis, the 

 tendon of digit iii. is connected with that of the perforated flexor 

 of the same digit by a strong slip near the insertion. Such a 

 connection is common in birds, and may be an archecentric 

 remnant of the original unspecialized condition of these tendons. 



Lle.rores perforati. — The pei'forated flexor muscles of digits ii., 

 iii., and iv, are closely similar in all these birds to the condition 

 that I have already figured (7. fig. 1) in Balearica. The only 

 points to mention are that the ambiens head in most cases is tied 

 to the head of the fibula by a strong ligament absent in Balearica, 

 and that in Otis the external head is very weak. 



Flexor profundus sen jjerforans and Flexor longushalhicis. — These 

 are present and are of the normal origin and general com'se in all 

 the Gruiformes including Otis, in \^"hich the hallux is absent. 

 The modes of junction of the tendons, however, are not all alike. 



The condition found in Eurypyga (text-fig. 85, A"II) appears to 

 me to be the most archecentric. The longus hallucis, as it does in 

 all the Gruiformes in which a hallux is present, sends a slip to the 

 hallux, and distal of this blends completely with the profundus 

 tendon in such a fashion that both tendons supply each of the 

 three digits. 



The condition in Heliomis (text-fig. 85, VIII) is an apocentric 

 Pboc. Zool. Soc— 1901, Vol. II. No. XLIII. 43 



