Essentials of Anatomy and Physiology

functional importance because the hip is a weight-
bearing joint, whereas the shoulder is not. Because the
acetabulum is deep, the hip joint is not easily dislo-
cated, even by activities such as running and jumping
(landing), which put great stress on the joint.
The femuris the long bone of the thigh. As men-
tioned, the femur forms a very movable ball-and-
socket joint with the hip bone. At the proximal end of
the femur are the greater and lesser trochanters, large
projections that are anchors for muscles. At its distal
end, the femur forms a hinge joint, the knee, with the
tibia of the lower leg. Notice in Fig. 6–14 that each
bone has condyles, which are the rounded projections
that actually form the joint. The patella, or kneecap,
is anterior to the knee joint, enclosed in the tendon of
the quadriceps femoris, a large muscle group of the
thigh.
The tibiais the weight-bearing bone of the lower
leg. You can feel the tibial tuberosity (a bump) and
anterior crest (a ridge) on the front of your own leg.
The medial malleolus, what we may call the “inner
ankle bone,” is at the distal end. Notice in Fig. 6–14
that the fibulais not part of the knee joint and does
not bear much weight. The lateral malleolus of the
fibula is the “outer ankle bone” you can find just above
your foot. Though not a weight-bearing bone, the

fibula is important in that leg muscles are attached and

anchored to it, and it helps stabilize the ankle. Two

bones on one is a much more stable arrangement than

one bone on one, and you can see that the malleoli of

the tibia and fibula overlap the sides of the talus. The

tibia and fibula do not form a pivot joint as do the

radius and ulna in the forearm; this also contributes to

the stability of the lower leg and foot and the support

of the entire body.

The tarsalsare the seven bones in the ankle. As

you would expect, they are larger and stronger than

the carpals of the wrist, and their gliding joints do not

provide nearly as much movement. The largest is the

calcaneus, or heel bone; the talustransmits weight

between the calcaneus and the tibia. Metatarsalsare

the five long bones of each foot, and phalangesare

the bones of the toes. There are two phalanges in the

big toe and three in each of the other toes. The pha-

langes of the toes form hinge joints with each other.

Because there is no saddle joint in the foot, the big toe

is not as movable as the thumb. The foot has two

major arches, longitudinal and transverse, that are

supported by ligaments. These are adaptations for

walking completely upright, in that arches provide for

spring or bounce in our steps. Important parts of hip

and leg bones are described in Table 6–4.

The Skeletal System 125

Table 6–3 BONES OF THE SHOULDER AND ARM—IMPORTANT PARTS

Bone Part Description

Scapula

Clavicle

Humerus

Radius

Ulna

Carpals (8)

• Glenoid fossa


• Spine


• Acromion process


• Acromial end


• Sternal end


• Head


• Deltoid tubercle


• Olecranon fossa


• Capitulum


• Trochlea


• Head


• Olecranon process


• Semilunar notch


• Scaphoid • Lunate


• Triquetrum • Pisiform


• Trapezium • Trapezoid


• Capitate • Hamate
  
  
  • Depression that articulates with humerus
  
  
  • Long, posterior process for muscle attachment
  
  
  • Articulates with clavicle
  
  
  • Articulates with scapula
  
  
  • Articulates with manubrium of sternum
  
  
  • Round process that articulates with scapula
  
  
  • Round process for the deltoid muscle
  
  
  • Posterior, oval depression for the olecranon process
    of the ulna
  
  
  • Round process superior to radius
  
  
  • Concave surface that articulates with ulna
  
  
  • Articulates with the ulna
  
  
  • Fits into olecranon fossa of humerus
  
  
  • “Half-moon” depression that articulates with the
    trochlea of ulna
  
  
  • Proximal row
  
  
  • Distal row
  
  
  
  

(text continued on page 128)