ANA TOMY OF BIRDS 289 



the ambiens that ensues as soon as the leg is bent upon the thigh, 

 and the tarsus upon the leg, the weight of the bird thus holding it 

 fast upon its perch. The effect is as if an elastic cord were tied to 

 the hip joint, thence directed over the front of the knee and back 

 of the heel and so on to the ends of the toes. Obviously, such a 

 cord would be strained when the limb is bent, relaxed when the 

 limb is straightened out. The reader may observe a corresponding 

 effect of the muscular arrangement of his forearm by throwing the 

 hand as far back as possible ; the fingers tend to close by the strain 

 on the flexors in passing over what is a convexity of the Avrist when 

 the hand is in that position. Passeres have no ambiens, the perfec- 

 tion of their feet in other respects answering all purposes. Birds 

 having it are termed homalogonatous or " normally-kneed " (Gr. 

 ofxaXos, homalos, from 6/xos, homos, like, even, etc. ; y6i>v, yovaros, 

 gonu, gonatos, knee) ; those Avanting it are called anomalogonatous, 

 " abnormally-kneed." The distinction prevails with much applica- 

 bility to various large groups of birds, and does good duty in 

 diagnosis when duly connected with other characters ; but surely 

 should not give name to primary groups founded upon it ! Other 

 muscles of the leg much used by the same sagacious and zealous 

 anatomist are the feniorocaudal, accessory femorocauclal, seniitendi- 

 nosus, and accessory semltendinosus. The whole five of these muscles 

 " vary ; any one or more than one may be absent in different birds ; 

 . . . the constancy of the iieculiarities in the different individuals 

 of each species, or the species of each genus, and very generally in 

 the genera of each family, makes it evident to any one working at 

 the subject that much respecting the affinities of the different 

 families of birds is to be learnt from the study of their myology, in 

 connection with the peculiarities of their other soft parts ; and that 

 these features will, in the long run, lead to a more correct classifica- 

 tion than one based on the skeleton alone, becomes almost equally 

 certain." (Garrod, P. Z. S., 1873, p. 630.) 



d. AnGIOLOGY : THE VASCULAR OR CIRCULATORY SYSTEMS 



Blood and Lymph are the two media by the circulation of 

 which throughout the body the various amoeboid animals which 

 compose the tissues are fed, their waste repaired, and their dead 

 parts removed. Each species oi Amceha has the faculty of selecting 

 from the constituents of blood and lymph its appropriate food ; and 

 of converting such nourishment into its own proper sul;)stance. 

 Refuse matters are either drained off by the kidneys and voided as 

 excrement, or swept by the current of blood into the lungs and 

 there cremated. The stream of lymph is a feeder to the blood, and 

 when the mingled currents are no longer distinguishable has become 



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