1901.] ANATOMY OP GRUIT^ORM BI-RDS. 647 



conditions in the G-ruinae, 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 he due either to a secondary 

 fusion of the medius and anterior, or to the anterior 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. 



Ilio-femo rails externuf: sen Glutceus anterior. — This variable 

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

 TR.E.) and is double in Cariama. 



Ilio-femoralis internum seu pectineiis. — This is present and fleshy 

 in all the Gruiformes. 



Amhiens. — 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 fixed 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 forms the " ambiens head " of the perforated flexor muscles 

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

 these in Balearica, 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 Crurceus 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 interims. The mass of the muscle (text- 

 fig. 79, FEM.-TIB.) 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 the distinctness 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. 



Oaiid-ilio-femoralis ( femoro-caudal and accessory). — The re- 

 searches of Garrod. 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 Gruiformes, the Eallidse, Heliornithidse, and some 

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

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



