1901.] A.KATOMT OF ORl/lKoKM UIBDS. «">47 



conditions in the Gruinae, where the medius is small in one form, 

 although quite separate, and absent in another, point towards such 

 a cause. On the other hand, the condition in Otis suggests that 

 the absence of a separate medius may be due either to a secondary 

 fusion of the medius and anterior, or to the auterior being a 

 primitive muscle in process of subdivision. However, whatever 

 view may turn out to be best founded, there is certainly no 

 correlation between the absence of the muscle, whether such 

 absence be archecentric or apocentric, and the archecentric and 

 apocentric conditions of the wing. 



llio-femorali* extemus sen Glut a as anterior. — This variable 

 muscle is present in all the Gruiformes (text-figs. 79 & 80, TL- 

 TR.E.) and is double in Cariama. 



nio-femoralis internus seu pectinevs. — This is present and fleshy 

 in all the Gruiformes. 



Ambiens. — This notable muscle is present in all the Gruiformes, 

 with the customary origin from the ilium, course down the back 

 of the thigh, passage through the knee-capsule, and insertion to 

 the flexors of the digits. In Cariama, however, what may be a 

 stage in reduction exists ; the tendon is immovably lixed in the 

 knee-capsule. This condition points in the direction of many 

 cases where the ambiens ceases at the knee-capsule, and it is to be 

 noted that this apocentricity occurs in a eutaxic member of the 

 Gruiformes. Below the knee the distal extremity of the ambiens 

 tendon forma the " ambiens head " of the perforated flexor muscles 

 of the toes. I have already figured (7. fig. 1) the arrangement of 

 these in Baleariea, and in the other Gruiformes the arrangement 

 is similar except that the ambiens head is reinforced by a strong 

 tendinous anchor from the head of the fibula. 



Femori-tibiales seu Crurams and Vastus. — The deep muscular 

 masses arising from the femur and passing to the tibia, or at least 

 to the knee-capsule, are present and well developed in all the 

 Gruiformes. The separate portion at the back of the thigh is in all 

 strong (text-figs. 81, 82, 83, 84, FEM.-TIB.I.). It is what is 

 usually termed the vastus internus. The mass of the muscle (text- 

 fig. 7'->, FEM.-T1 It.) which lies immediately under the ilio- tibialis, 

 with which, as I have mentioned, it is frequently fused towards 

 the knee, is practically identical in all; but there is specially to be 

 noted 1 he dial inn ness of a deep slip of the muscle-mass (text-fig. 79, 

 FEM.-TIB.E.) with a separate origin and insertion. This slip, 

 frequently absent in birds, is present in all the Gruiformes, but is 

 much smallest and weakest in Heliornis. 



Caitd-iHo-femoralis (femoro-caudal and accessary). — The re- 

 searches of Ghurod, Beddard, Gadow, and others have made it 

 plain that the presence of two divisions of this muscle is the 

 archecentric condition for birds, and that deviations from this, 

 consisting of the reduction of either or of both, are apocentric. 

 Among the Qrniformes, the EtaUidss, Heliornithids, and Borne 

 Cranes alone display both muscles. In Eurypyya Garrod (5) 

 found both present, hut in the specimen that I examined the iliac 



