Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/1040/
1030- 
THORAX. 
ence to the spine. But the relation of these 
torsions to the spine are different : the pos¬ 
terior torsion is relative to the spine late¬ 
rally, while the anterior torsion relates to 
the spine more in the antero-posterior direc¬ 
tion : they both conspire to increase the obli¬ 
quity of the rib in one given direction,—from 
above downwards. 
The torsion of the 1st rib, we have noticed, 
is directed in a contrary direction to that of 
other ribs ; and we have observed that the 
presence of torsion in general favours 
muscular traction : but the 1st rib is an 
exception to this ; here the torsion exists 
only between its two chief articulating pro¬ 
cesses, — the head and the tubercle : in the 
other ribs the torsion is between the tu¬ 
bercle and the body of the bone. The pos¬ 
terior torsion of the 1st rib appears to be 
merely destined to afford the head a more 
complete attachment to the body of the one 
vertebra (the 1st dorsal) to which that rib 
is fixed. A posterior torsion, in this short 
rib, is not needed for muscular traction, be¬ 
cause here the scaleni are placed in the most 
favourable position — nearly at an angle of 
90° with reference to the body of the bone 
in question, while their other insertion into 
the cervical vertebrae facilitates the most ex¬ 
tensive and favourable means for its mobility, 
independently of any favouring twist in the 
rib for that purpose. 
(4) Surfaces (special differences). — The 
thorax being conical, or somewhat barrel¬ 
shaped, it follows that the surfaces of 
the ribs, like the hoops of a very spherical 
barrel, must gradually change their direc¬ 
tion ; thus the surfaces of the 1 st rib are 
nearly superior and inferior, this bone forming 
the lid to the thorax, while the surfaces of the 
6th or 7th rib are external and internal, and as 
we proceed downwards to the 10th, 11th, and 
12th ribs, the surfaces are again slightly 
tending towards a superior and inferior po¬ 
sition, so that the internal surfaces of the 1st 
and 12th ribs are directed somewhat towards 
each other. The body of the rib, or that 
part which covers the lung laterally, and the 
anterior and posterior extremities, have also 
their surfaces inclined in different directions. 
Thus, take a perfect rib, say the 7th, laterally 
to the thorax the two surfaces are internal 
and external, while at the anterior end they 
are directed — external surface, forwards and 
downwards ; internal surface, upwards and 
backwards ; —at the posterior end, — external 
surface, upwards and backwards ; internal 
surface, downwards and forwards. This is 
produced by their respective torsions. In 
some of the lower animals the ribs overlap 
each other like the tiles of a house; this 
sometimes threatens in man, particularly in 
diseases of the spine (fig. 666.), when they 
closely approach each other. 
(5) Specific differences of the extremities of 
the ribs. — The greatest difference is in the 
posterior end of the rib. The anterior pre¬ 
senting little difference. 
(a) Anterior extremity.— These are ail hol¬ 
lowed out for their cartilage. As the ribs 
become more perfectly developed, for in¬ 
stance, the 5th, 6th, 7th, and 8th, the an¬ 
terior extremity is broader, but not more 
deeply hollowed out than some of the other 
ribs, which are less perfectly developed, as in 
the 2nd and 3rd, or 11th ribs. This extremity 
is most pointed in the 12th rib. 
Fig. 666. 
Relation of the ribs to the spine in angular curvature. 
(b) Posterior extremity. — The posterior ex¬ 
tremity of the rib is more complicated, and 
has certain named parts, as the head, neck, 
tubercle, and angle, all of which become modi¬ 
fied as we pass from above downwards. Their 
differences may briefly be noticed. 
ls£ Of the head.— On the head of the rib, 
articulating with the vertebrae, a surface or 
facet is formed. The 1st, the 11th, and the 
12th ribs articulate each with the body of one 
vertebra, and therefore they have one arti¬ 
culating surface. All the rest articulate each 
with the bodies of two vertebrae, and they 
consequently have two such articulating sur¬ 
faces as already described. The head of the 
1st rib is relatively larger than that of the 
others. For the most part, as the ribs in¬ 
crease in size, the head likewise increases, 
so that in the best developed rib the head and 
its surfaces are most perfectly formed, dege¬ 
nerating again to the 12th rib. 
2nd Of the neck. — The neck being that 
part of the rib between the articulation of 
the rib with the bodies of the vertebra, and 
that with the transverse process, and these 
points differing but little in their distance 
from each other in the dorsal vertebrae, it 
follows that the absolute length of the neck 
of the different ribs is nearly the same. The 
necks of the ribs differ in their thickness, ac¬ 
cordingly as their respective ribs increase or 
diminish in size ; therefore, in the middle
        

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