16'4 MUSCULAR SYSTEM. 



ceous animals. The ylutei (A. 0,) the iliacus internus, 

 and the psoas, are strong muscles in the land species, as are 

 almost all the extensors and flexors of the thigh-bone. The 

 biceps cruris, (A.v,) and the semitendinosus, (A. w,) form long 

 muscular bands behind the femur, and the rectus femoris, 

 (A. #,) in front, which unites below with the vastus externus, 

 (A. y,) the vastus internus, and the crureus, to be inserted 

 into the tuberosity of the tibia, below the knee, by a common 

 tendon. The sartorius (A. z,) semimembranosus, obturator, 

 and graciliSy have here their usual position and action. The 

 extensor communis digitorum pedis, (A. 1,) and the short ex- 

 tensors of the four toes, (A. 5,) resemble the corresponding 

 muscles of the hand. The peroneus, (A. 4,) the gastrocnemii 

 (A. 3,) and the other extensors, are strong on the posterior as 

 those on the anterior extremities in the tortoises, to support 

 and move their heavy body on the land, but they are scarcely 

 perceptible in the long flat fin-like feet of the turtles. The 

 cloaca has its dilating and its sphincter muscles, and the 

 highly moveable tail has its numerous flexors and its exten- 

 sor muscles in the reptiles of this order, and even the glottis, 

 the penis, and the clitoris, have already their accompanying 

 muscles developed, as in higher animals. 



The muscles of birds are more red and vascular, more 

 irritable and dense than in the cold-blooded vertebrata be- 

 neath them, and they possess these properties in the greatest 

 degree in the rapaceous tribes, where the respiration is great- 

 est, and where all the functions are most energetic. This 

 condition of the muscular system is required in birds, from 

 the lightness of the medium through which they move, and 

 from their quick and long continued movements through that 

 element. The muscles are more feeble, pale, soft, and pala- 

 table in the heavy, slow-moving, phytophagous tribes, where 

 the condition of the bones and most of the other systems, 

 mark an inferior or reptile state of development. The fleshy 

 parts of the muscles are generally short and thick, especially 

 in the arms and legs of birds, and their tendons are generally 

 long, slender, dense, and often ossified, like many cartilagi- 

 nous parts of the skeleton. The active, heavy, fleshy parts 

 of the muscles being situate, for the most part, on or near 

 the solid trunk of the bird, the extreme parts, so important 

 for progression, are lightened by receiving and supporting 



