1901.] AHATOMY OF 6BUIT0BM BIBDB. Go^ 



Gastrocnemius. — Apart from the middle or posterior femoral 

 head, which I have discussed above in connection with the femoral 

 insertion of the caud-ilio-nexorius, the archecentric condition of 

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

 anterior femoral head, with 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 Cariama, 

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

 sling is attached and which lies under the separate deep slip of the 

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

 both these heads are present, and there is a third head to which 

 the biceps is superficial. Tn Eurypyga there are three heads with 

 similar relations. in Heliornis the anterior femoral head i< 

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

 found respectively in Cariama and Otis. 



The middle and outer heads of the gastrocnemius show marked 

 variations amongst the Gruiformes. but these do not present any 

 definite correlation with the apocentric and archecentric conditions 

 of the wing. 



Sole)'*. — This muscle is present in all, and has the origin (text- 



"1 . 82, 83, 84, SOL.) normal in birds ; its tendon parses down 



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



FUxores perforantes et perforati. — The superficial llexors <>f 

 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 fuse> 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 Psophia obscum and Heliornis, 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 he an archecentric 

 remnant of the original unspecialized condition of these tendons. 



flexures perforati. — The perforated flexor muscles of digits ii., 

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

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

 points to mention are that the ambiena head in mosl cases is tied 

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

 ami that in Otis the external head is very weak. 



Flexor profundus sen perforans and Flexor longus hull mix. — These 

 are present and are of the normal origin and general course in all 

 the Gruiformes including Otis, iii which the hallux is absent. 

 Tie* modes of junction of tin- tendons, hov ever, are not all alike. 



The condition found in Eurypyga (text-fig. s ">. VII) appears to 

 lie- to lie tie- mosl archecentric. The longus hallucis, as it docs in 

 all the Gruiformes in which a hallux is present, sends a -!i|> to the 

 hallux, and distal of this blends completely with tie' profundus 

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

 three digits. 



Tie- condition in UsUomis (text-fig. 86, VIII) is an apocentric 



Pboc. Zoot,. 8oc.— 1901, Vol. II. No. XLII1. 13 



