506 
MR. S1BSON ON THE MECHANISM OF RESPIRATION. 
The Chameleon, §§ 12-16, Plate XXIII. fig. II. 
12. The Chameleon, though a cold-blooded animal, whose movements are for the 
most part sluggish, and whose breathing is slow and irregular, yet stands in need of 
occasional very deep inspirations and very sudden and complete expirations. 
13. Has a sternum, and long costal cartilages in addition to the ribs. 
The Chameleon has a greater portion of rib movement than almost any other four- 
legged creature. The ribs, which are long and slender, yet strong, are eighteen in 
number; the lowest rib is at a very short distance from the pelvis. The first and 
second ribs have no cartilages ; the rest, excepting the last, have long, firm, slender 
cartilages, attached by very flexible almost tendinous intermedia to the ends of 
the ribs. The costal cartilages of the third, fourth and fifth ribs, are attached to 
the sternum. They resemble closely the costo-sternal ribs of birds. The remainder 
have their anterior extremities free. 
The addition of a complete system of anterior ribs or moveable cartilages gives the 
Chameleon a double power over the Snake for the expansion of its lungs. I defer 
considering the mode in which the anterior ribs act in expanding and narrowing the 
chest, until I describe the mechanism of breathing in birds, as it is so much more 
intelligible and explicable in the Bird than in the Chameleon. 
14. Inspiratory muscles acting on the ribs, Plate XXIII. fig. II. 1 .5.6.7- 
The scalenus (1), the levatores costarum (5.6), and the external intercostals (j), have 
the same action and nearly the same anatomical distribution that they have in the 
Snake. They combine to elevate the ribs, push forwards their anterior ends, and 
draw backwards their posterior curves; they thus deepen and widen the chest. The 
fibres of the external intercostal muscles between the first and second, and second and 
third ribs, have the same direction with those of the scalenus, of which indeed they 
seem to be a continuation, the ribs being interposed. 
In addition to these muscles, there is between some of the ribs another external 
intercostal (7), whose fibres are superficial to, and less oblique than the usual external 
intercostal. 
15. Inspiratory muscles of the cartilages, Plate XXIII. fig. II. 9. 
The first costal cartilage is raised by a strong triangular muscle arising from the 
sternum (9) ; strong muscular fibres pass from the first cartilage to the second, and 
raise it on inspiration ; the rest have between them webs of aponeurotic tissue. 
16. Expiratory muscles, Plate XXIII. fig. II. 31.21.32.30.19.17- 
In expiration a series of small muscles (31) lower the ribs; each arises from the 
vertebra to be inserted into the lower edge of the rib above. 
