616 MUSCULAR SYSTEM 



tarse. Tendon A goes to ii. iii. and iv. Tendon P to i. and by 

 vinculum to ii. also, consequently, owing to the vinculum's distal 

 position, its action is confined to two toes. This type, to a certain 

 extent intermediate between I. and II., is characteristic of Acci- 

 pitres, except Cathartidse (see V.), and Pandion, in which last, 

 perhaps owing to its reversible outer toe, A goes to ii. iii. and iv., 

 but tendon P splits into 4, sending a slip to each toe directly, 

 and in this case is therefore a complete flexor communis. 



IY. The prevalent type where the hallux is absent or very 

 small. Both muscles are strong and almost equally developed, 

 their tendons unite about the middle of the metatarse, the joint 

 tendon A + P going to the front toes, the hallux receiving no 

 tendon, and consequently there is no crossing. This type, genetically 

 connected with II. , occurs in Casuarius, Drom&us, Rhea, Struthio, 

 Turnix, Pterodes and Phcenicopterus, Palamedea, Dicholophus, Tubin- 

 ares, ColymU. 



V. Tendons A and P unite at a variable distance below the 

 ankle joint, passing it in the ordinary way, and there is no crossing 

 behind the metatarse, tendon P running directly into A from its 

 fibular side. Muscle A generally much stronger than muscle P. 

 In the simplest case (V, a) the united tendons A + P split into 4 

 equally strong tendons, either just above the base of the toes, or 

 successively first to the hallux and lastly to iv. as in Buceros, 

 Cypselus and Colius. Secondly an exaggerated condition of this 

 (V,a) prevails (as V,b) in Momotidw, Todidaz, Meropidae and in some 

 Alcedinidse, where the tendon of the hallux is split off directly 

 from the tibial and ventral side of A above its fusion with P. 

 Thirdly there is a condition (V, c), hitherto known in the Trochilidse 

 only, where A and P are completely divided from each other into 

 a deep mass (A) which goes to ii. and iii., and into a plantar mass 

 supplying i. and iv. Careful and, from their small size, difficult 

 preparations of this have been made by Prof. Stewart and Mr. 

 Bourne for the Museum of the College of Surgeons in London, and 

 any other description and figures of these Trochiline tendons are 

 either incorrect or misleading. Lastly comes the modification found 

 in the Cathartidse, where the fusion of the two principal tendons (as 

 in Y,a and V,b) is followed by a splitting into a ventral mass (P) to 

 ii. iii. and iv., and into a deep mass (A) to i. ii. and iii. This 

 arrangement can be easily derived from type V, a, but almost 

 equally well from the variable type III., as indicated by Pandion 

 (fig. XL) In the latter case the Cathartidse would appear as a 

 peculiar departure from primitive Accipitrine conditions. 



VI. Vinculum present, going from P to A. Tendon A single, 

 going only to iii. Tendon P going to i. ii. and iv., and by the 

 vinculum to iii. also, i.e. to all the toes. This most peculiar type 

 prevails in all the anomalogonatous zygodactyl Birds, Picidw, Rham- 



