Functional Morphology - Nonhuman Primates in Biomedical Research - page 108

each first digit has two phalanges, whereas all of the other
four digits have three phalanges.
The bones of the forelimb differ from those of
many other mammals primarily in the presence of a well-
developed, usually robust clavicle which articulates with
both the manubrium of the sternum and the acromion
process of the scapula. It is a fully developed long bone
which serves as a strut for the lateral positioning of the
shoulder joint and contributes to the broadening of the
shoulders. The body of the clavicle has a ventral convexity
proximally and a ventral concavity distally. When rotated
longitudinally the resultant movement is similar to that of
a crank handle. The scapula is also well developed and may
be positioned more dorsally in primates than in other
quadrupeds ( Figure 4.8C ). Overall, many characteristics of
the pectoral girdle correlate with the evolutionary trends
towards a broadening and flattening of the thoracic cage
retained in many higher primates.
The shape of the humerus, particularly the direction of
the head and the longitudinal rotation (torsion) within the
shaft, reflects the locomotor behavior of the species. The
ulna and radius are fully developed, independent bones
whose proximal and distal articulations allow for consid-
erable longitudinal rotation of the forearm. The amount of
pronation and supination (longitudinal rotation) of the
forearm varies greatly among species and can be generally
correlated with the need for forearm flexibility in loco-
motor behavior. Marked elongation of the humerus, ulna,
and radius characterize species with locomotor repertoires
that include brachiation, semibrachiation, or arm-swinging.
The length of the olecranon process of the ulna shows
considerable variation among primates and the maximum
range of elbow extension can be as high as 180

prehensile hand. Other than robustness and relative lengths,
the long bones of the hands of higher primates differ little
from those of humans except for: (1) the carpometacarpal
joint of the thumb in Cebidae; (2) the vestigial nature of the
thumb in three species; and (3) the claws on the distal
phalanges of Callitrichidae (see the descriptions of hands
and digits in the sections “Nails or claws” and “Overview
of limbs” above). A further osseous difference between
humans and nonhuman primates is that sesamoid bones are
frequently found in the tendons of muscles in the hands of
the latter.

Skeleton of Hindlimb
The bones of the hindlimb include a pelvic girdle that is
very similar to that of other quadrupedal mammals
( Sullivan, 1933 ) and differs markedly from the short, wide
pelvic girdle of humans. The pelvic girdle is formed by the
two os coxae which articulate with either side of the
sacrum. Each os coxae is formed by the fusion of usually
four bones: the ilium, ischium, and pubis as well as a small
bone, the os acetabula. This latter bone fuses with the ilium
very early in development and is frequently considered
a part of it. The long, narrow blades of the ilia lie in para-
sagittal planes and give the pelvis a typically mammalian
quadrupedal orientation, i.e. the pubic symphysis is mark-
edly caudal to the plane of the sacral promontory
( Figure 4.12E ). In Old World monkeys and lesser apes the
ischial tuberosities are covered by specialized skin called
ischial callosities (for further discussion of these see the
section “Skin” above). The bony configuration of the pelvic
girdle in nonhuman primates makes it one of the few areas
of the body where their anatomy is more similar to other
types of mammals than to humans. This similarity,
however, is limited to the bony pelvis and the orientation of
the skeletal muscles which attach to it since the internal
organs of nonhuman primates more closely resemble those
of humans than of other mammals (see the sections
“Abdominal

in

brachiators.
The carpus is composed of eight or nine short bones that
are roughly arranged in two rows ( Figure 4.3 ). In most
nonhuman primates the os centrale is a separate bone, but in
some it is fused with the scaphoid. The names of the other
eight carpal bones are the same as those in humans:
scaphoid, lunate, triquetrum, and pisiform in the proximal
row from lateral (radial) to medial (ulnar) and trapezium,
trapezoid, capitate, and hamate in the distal row from
lateral to medial. As in humans the carpus is markedly
concave on the palmar surface. This forms a deep carpal
tunnel which transmits both the extrinsic flexor muscles
and the major vessels and nerves of the hand. The
nonhuman primate carpus differs markedly from that of
humans in only three respects: (1) the regular presence of
an os centrale; (2) the large size of the pisiform relative to
the triquetrum; and (3) the consistent presence of a large
sesamoid bone near the trapezium.
With the exception of reduced thumbs in a very few
taxa, the metacarpals and phalanges are generally all well-
developed long bones and contribute to a highly mobile and

and pelvic morphology” and “Perineal

morphology” below).
The femur is the single bone in the proximal segment of
the hindlimb. The shape and robustness of the bone as well
as the length and angle of the femoral neck vary among
species depending on locomotor pattern, but almost all
higher primates lack a third trochanter. The associated
patella articulates only with the ventral (anterior) distal
femur. The tibia and fibula of the more distal segment are
both well-developed, independent long bones which artic-
ulate both proximally and distally. The shape of these two
bones as well as that of the patella are very similar to those
in humans.
The tarsus of nonhuman primates is composed of seven
short, irregular bones: the talus, navicular, calcaneus,
cuboid, and three cuneiforms, lateral, middle, and medial