Functional Morphology - Nonhuman Primates in Biomedical Research - page 117

ribs and bony pelvis laterally, and the pelvic diaphragm
caudally (inferiorly) ( Figure 4.12E,F ). The morphology of
the vertebrae is described with the back (see the section
“Skeleton” above). The bony pelvis is described in detail
with the bones of the hindlimb (see the section “Skeleton of
hind limb” above). The shape of the bony pelvis in
nonhuman primates is similar to that of other quadrupeds.
The blades of the ilia are elongated in a cranial

The four-part compartmentalization of their stomach,
however, is not as complete as that seen in ruminants nor is
there any regurgitation of food. Enlarged colons (and
cecums) serve a similar function in folivorous New World
monkeys, apes, and other Old World monkeys. Gut size,
motility and transit time vary widely among species of
nonhuman primates and the link between phylogeny, body
size, diet, gut length, and gut transit time has not been fully
explored ( Milton and Demment, 1988; Stevens and Hume,
1995; Remis, 2000; Lambert, 2002; Remis and Dierenfeld,
2004 ). A vermiform appendix is found only in apes (and
humans).
The accessory digestive organs include the liver,
gallbladder, and pancreas. The spleen is not a digestive
organ, but it develops within the dorsal mesentery of the
stomach and thus is closely associated with the gastro-
intestinal system. The liver is a large organ in the cranial
(superior) abdomen which is expanded far more to the left
than in humans to occupy an extensive region caudal
(inferior) to the respiratory diaphragm ( Figure 4.12A,B ).
It most commonly has three large distinct lobes (left, right,
and central or median) and two smaller ones (caudate and
quadrate). The connective tissue separation between the
left lateral lobe and the central lobe is well defined, but
that separating the right lateral and central lobe is not. The
quadrate and caudate lobes are small and the latter nearly
surrounds the caudal (inferior) vena cava ( Figure 4.12B ).
The internal structure of the liver is similar to humans and
lacks clearly defined connective tissue septa between
adjacent liver lobules ( Vons et al., 2009 ). The relation-
ships of the hepatoduodenal ligament, ligamentum teres,
and other ligaments are similar to those of humans. The
gallbladder lies against the caudal surface of the central
lobe.
The spleen (lien) develops in the dorsal mesentery and
is suspended by mesenteric connections to adjacent organs.
It is situated in the dorsolateral (posterolateral) aspect of
the cranial (superior) left quadrant of the abdomen
( Figure 4.12C ) and is structurally similar to that of humans.
As in humans, the spleen has a collagenous, not muscular,
capsule.
As in other mammals the pancreas develops as two
parts, one each in the dorsal and ventral mesenteries.
During development these two parts fuse to form a single
pancreas. The pancreas lies dorsal (posterior) to the
stomach, and its long axis is positioned transversely. The
head lies adjacent to the duodenum which receives the two
pancreatic ducts. The tail lies near the hilum of the spleen
( Figure 4.12C ). The body of the pancreas is partially fused
to the dorsal (posterior) abdominal wall and, as in humans,
is secondarily retroperitoneal except for the tip of the tail.
The dual functions of the pancreas are evident in the
interspersing of islets of Langerhans among the exocrine
glandular tissue.

caudal
direction and the iliac crest usually lies adjacent to the
caudal portion of the last lumbar vertebra. The axial
(transverse) plane of the pubic symphysis lies caudal to the
axial plane of the sacroiliac joint ( Figure 4.12D

e

F ). Thus,
as in most other mammals, during parturition the fetal head
is able to negotiate the sacral promontory before the pubic
symphysis rather than simultaneously as in humans.

e

Gastrointestinal System and Spleen
The gastrointestinal system includes both the tubular gut
and the associated digestive glands ( Lineback, 1933a;
Chivers and Hladik, 1980 ). The first part of this tube, the
pharynx, is a shared pathway for both the respiratory and
digestive systems. (See also the pharynx in the sections
“Oral cavity” and “Neck viscera and thyroid and para-
thyroid glands” above.) Caudally the pharynx continues
directly into the esophagus. In nonhuman primates the
pathway from mouth to pharynx to esophagus to stomach is
almost a direct line. This differs considerably from humans
where flexion of the basocranium positions the face below
the anterior cranial fossa, thus positioning the pharynx at
a right angle to the oral cavity.
The segments of small intestine, comprising duodenum,
jejunum, and ileum, are quite similar to humans in position,
blood supply and lymphatic drainage, and innervation,
although extensive plicae circulares, such as are found in
humans, are lacking internally ( Lineback, 1933a ). All
primates have cecums and relatively enlarged colons when
compared to most other mammals. All primates lack the
ability to digest cellulose ( Chivers and Hladik, 1980 ), and
none chew their cud. Digestive system adaptations parallel
dietary preferences and, to an extent, both can be correlated
with overall body size, although there are numerous
exceptions ( Fleagle, 1999 ). Smaller species tend to be
insectivores whereas large species tend to be folivores.
Frugivorous primates include the entire spectrum of body
sizes. Small frugivores frequently supplement their diet
with insects whereas large frugivores supplement with
leaves. Most of the adaptations of the digestive system seen
in primates are found in folivores and occur in the stomach,
cecum, and/or colon. In folivorous species the digestion of
cellulose is performed by colonies of microorganisms
living in dilated regions of the digestive system. Some
folivorous Old World monkey groups such as Colobines
have an enlarged stomach which allows for fermentation.