NO. I LOCOMOTOR MECHANISMS OF BIRDS HARTMAN 21 



species in the same family, it will be recalled that there are some 

 exceptions. In the herons the range of the pectoralis is from 10 to 

 17 percent of the body weight; in the flycatchers, from 12 to 22 per- 

 cent; in the swallows, from 14 to 21 percent. 



Supracoracoideus. — The supracoracoideus, one of the principal leva- 

 tors of the wing, appears to be of little importance in many birds, 

 judging from its size. In our studies it ranged from about 0.40 percent 

 of the body in species of the genus Buteo to 11.5 percent of the body 

 in the trochilids, or 1.8 to 30 percent respectively of the flight muscles. 

 High values (table 1) are found in Crypturellus, Chamaepetes, Odon- 

 tophorus, Numida, Capella, trochilids, doves, Pyrrhura, and Manacus. 

 Low values appear in Phalacrocorax, Buteo, Pandion, Caracara, Piaya, 

 Tyto, and Pulsatrix. The supracoracoideus of Nyctibius (3.18 percent 

 of the flight muscles) is much smaller than that of Nyctidromus 

 (6.9 percent of the flight muscles). There is a great difference in this 

 muscle in Manacus (14.2 percent of flight muscles) as compared to 

 that in Chiroxiphia (6.0 percent of flight muscles). Likewise, this 

 muscle is larger in Cotinga ridgwayi (7.76 percent of flight muscles) 

 than in Querula (4.56 percent of flight muscles). 



The range of supracoracoideus among different families is shown in 

 figure 3. It will be noted that the greatest differences are to be found 

 in the larger birds, the muscle being largest in those birds that make a 

 quick takeoff. It is especially small in cuculids, tytonids, and strigids. 



"Rest." — The combined muscles of the shoulder, brachium, and 

 forearm (except those noted above), which appear in the table under 

 the heading "Rest," are shown in figure 4. With fewer exceptions 

 than in the other muscle groups, they tend to follow a straight line. 

 Among the lowest are the grebes, rallids, certhiids, and sylviids. 



Division of this group of muscles into shoulder, brachium, and 

 forearm shows variations among the different families and among 

 some species of the same family. This has been done for 67 species 

 distributed among 32 families. Typical examples have been chosen 

 in table 3 (p. 89). The shoulder group shows low values in Anhinga 

 (1.04 percent), Ardea (1.47 percent), Polyborus (1.60 percent), 

 Ereunetes mauri (1.13 percent), Thalasseus (1.37 percent), Columba 

 livia (1.26 percent), and Crotophaga (1.60 percent). It was high in 

 Tinamus (3.44 percent), Heterocnus (3.07 percent), Chondrohierax 

 (3.30 percent), Ortalis (3.34 percent), Colinus (3.42 percent), Co- 

 lumba speciosa (3.15 percent), Megaceryle (3.25 percent), and Mnio- 

 tilta (4.46 percent). These muscles were larger in Colinus (3.42 per- 

 cent) than in Odontophorus (2.05 percent) and Gallus (1.61 percent). 



