112 ANATOIMY OF VERTEBRATES. 



and eighth ribs. The fibres pass forward and join those of the 

 preceding muscle, to be inserted into the scapular integument. 



The three preceding muscles are broad and thin, but Avell- 

 defined; they would appear to influence the movements of the 

 rudimentary spur-armed wing through the medium of the integu- 

 ment, as powerfully as do the rudimental representatives of the 

 true muscles of that extremity. 



There are also two muscles belonging to the cutaneous series, 

 and inserted directly into the bones of the wing. One of these, 

 the dermo-ulnaris, is a small, slender, elongated muscle, which 

 takes its origin from the fascia beneath the dermo-costalis ; its 

 fibres pass backward, and converge to terminate in a very slender 

 tendon which expands into a fascia, covering the back part of the 

 elbow-joint. It extends the elbow-joint and raises the wing. 



The dermo-humeralis is also a long and narrow strip, deriving 

 its origin from scattered tendinous threads in the subcutaneous 

 cellular tissue of the abdomen : it passes upward, outward and 

 forward, and is inserted fleshy into the proximal part of the 

 humerus, which it serves to depress. 



The cutaneous muscles which spread the plumes of the peacock 

 and raise the hackles of the cock are unusually developed in these 

 birds. 



§ 136. Locomotion of Birds. — Upon land, the trunk is ba- 

 lanced horizontally on an axis traversing the acetabula perpen- 

 dicidarly to the plane of the medial section. The centre of 

 gravity is brought within the base of support by the advanced 

 position of the thigli-joints in the pelvis, and by the transference 

 of the weight from the femoral heads by the shafts inclining for- 

 ward to the heads of the tibia?. The area of the base of support 

 is adjusted to the same end by the anterior extension and diver- 

 gence of the three longest toes. On this base the stilt-like leg 

 of the crane, rising like a straight slender column to the capital 

 formed by the head of the tibia, is capable, by an outward as 

 well as backward course of the femur to its joint-cup, of sus- 

 taining the l:)ody singly : the neck of the bird being so bent, and 

 the head so disposed, as to throw the centre of gravity over the 

 vertical line passing through the base of support. Thus sleep 

 the GrallcB and allied Palmipeds (Flamingos, Anserines), adjusting 

 by reflex action the superincumbent weight as they may be 

 swayed by the wind on the long and taper pedestal. In standing 

 on two feet, the tibia and metatarse are usually, in Birds, bent at 

 an open angle. 



Progression on land is effected in most Birds by alternate ad- 



