MR. SIBSON ON THE MECHANISM OF RESPIRATION. 
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21. The internal intercostals (§§ 48.49.61.85). 
21 1 . In the Chameleon and Snake (figs. II. I.) an infra-costal muscle passes from 
the upper edge of one rib to the rib but one above (§§ 1 1.16). 
21 a. In the Hawk (fig. IV.) there is an infra- costal from the eighth to the sixth rib. 
In the Stormy Petrel (fig. V.) a muscle acts from the pelvis on the lowest rib. 
22.23.24. Digastricus, and its varieties. 
In the Monkey and Ass (figs. XV. X. Archives of the Royal Society) the digas- 
tricus is two-bellied, as it is in Man ; it is replaced in the Seal and Rabbit (figs. 
VIII. XI.) by two muscles arising from the mastoid processes inserted, one into the 
hyoid bone, the other into the lower jaw ; and in the Dog (fig. X.) by one muscle to 
the lower jaw. The Porpoise (fig'. XVI. b. Archives of the Royal Society) has a 
powerful genio-hyoid in lieu of the digastricus. 
2 7. In the Porpoise (fig. VII.) a muscle passes from the cervical vertebrae to the 
ribs, resembling a scalenus (§ 74). 
28. Omo-hvoid in the Monkey (fig. XV. Archives of the Royal Society). 
29. In the Fowl and Stormy Petrel (figs. III. a. IV.) a muscle acts from the su- 
perior ribs on the scapula to raise it (§ 25). 
30. The sacro-lumbalis is shown in the Ass (fig. X. Archives of the Royal Society). 
In the Chameleon and Fowl (fig. II. III.) an analogous muscle arises from the pelvis 
to be inserted into the ribs (§§ 16.26.54.66.94). 
30. In the Snake (fig. I.) represents a series of muscles that pass from rib to rib 
and serve as muscles of progression (§3). 
31. In the Stormy Petrel (fig. V.), 
31 and 32, in the Fowl (fig. III. a.), are muscles acting from the scapula to raise 
the ribs during inspiration (§ 25). 
31. In the Snake and Chameleon (figs. I. a. b., II.), are muscles acting from the 
dorsal vertebrae to lower the ribs (§§ 1 1.13.16). 
32. In the Chameleon (fig. II. b. Archives of the Royal Society) are muscles acting 
from the vertebrae on the ribs to narrow the chest (§ 16). 
32.34. In the Snake (fig. I. b.) are muscles acting from the vertebrae on the ribs 
to raise them (§ 10). 
33. In the Snake is a muscle passing from rib to rib near their vertebral articula- 
tions (§ 10). 
PLATE XXIII. 
Figs, l.a.b. (figs. I. c.d.e. Archives of the Royal Society). The muscles of respiration 
in the Snake (§§ 3-11). 
Fig. II. (figs. II. b.c.d. Archives of the Royal Society). The muscles of respiration in 
the Chameleon (§§ 12-16). 
4 b 2 
