#60] ANNUAL REGISTER, 
traction of the recti muscles, inserted 
into and covering them, move over 
each other, and thus the circle of 
the sclerotica will be diminished, 
and of course the cornea, which is 
immediately within the circle made 
by these scales, will be pressed for- 
wards, or, in other words, rendered. 
more convex, and thus the focus of 
the eye becomes altered, its axis 
being elongated. This construction, 
and consequent convexity of the 
cornea, must render small objects 
near the animal very distinct. 
On these muscles relaxing, the 
elasticity of the sclerotic coat will 
restore the cornea to its original 
flatness ; it thus becomes fitted for 
viewing objects placed ata greater 
distance from the eye, and this will 
be in proportion to the degree of 
relaxation. 
There seems toexist in nature an 
economy of motion, to prevent fa- 
tigue and exhaustion of the abimal 
powers by continued voluntary mus- 
cular action. If two opposite ac- 
tions of the same frequency occur in 
two muscles, the one being antago- 
nist to the other, the action of one 
ceasing, the action of the other must 
take place previously to farther mo- 
tion of the part; for instance, on the 
- biceps flexor of the arm acting, the 
arm will be bent, but on discontinu- 
ing its action the arm will remain in 
the same state, unless it was straight- 
ened by the action of the bicepts 
exterior, its antagonist ; but where 
one action in a part is required to 
take place almost constantly,and the 
opposite action but.seldom, to save 
the animal from fatigue necessarily 
induced by muscular contraction, - 
she gives an elastic ligament, which 
from its elasticity may be said to be 
in continual action, without ex. 
hausting the animal. Thus, when 
1793. 
the opposite action, which is of less 
‘frequent occurrence, is required, it 
is performed by overcoming the re- 
sistance, or elasticity of this elastic 
ligament, which, on the muscle giv- 
ing over its action again, resumes its - 
former state. The elastic cartilages 
of the ribs performing, in some de= 
gree, the functions of a muscle, are 
of use in fespiration ; likewise the 
elastic ligaments which support the 
claws of all the feline genus, keep- 
ing them from friction against the 
ground. ‘These claws, at the voli- 
tion of the animal, by muscles ap- 
propriated for that purpose, are 
brought into action or extended. 
From theabovementioned structure, 
the same thing appears to take place 
in the eyes of animals. When an 
animal is desirous of seeing minute 
objects, the recti muscles act, and 
thus, by rendering the eye more 
convex, enlarge the angle under 
which the object is seen. How ne- 
cessary is this structure to these ani- 
mals in particular ; for, without ita 
bird would be continually exposed 
to have its head dashed against a 
tree when flying in a thick forest, 
its motions being too rapid for the 
common structure of theeye. The 
eagle, when soaring high in the 
air, observes small objects on the 
earth below him, inconceivable to 
us, and darts upon them instanta- 
neously. Here we must allow that 
there must be an extraordinary ale 
teration in the focus in this eye, in 
almost an instant of time. How 
could this be performed unless the 
animal had this apparatus? The 
eyes of quadrupeds, as I shall after- 
wards shew, can perform this altes 
ration, though notin the same degree, 
as it is not necessary, their modes of 
life being different. A swallow, |) 
sailing through the air, pursues a 
great |) 
