**3. Osteology**

The general build of the skeleton of the rhesus monkey is illustrated in **Figure 6**. The skull is large and heavy compared to the slender body. This contrasts with the sturdy external appearance of the rhesus monkey, as depicted in **Figure 1**, which suggests that this species has a well-developed musculature.

#### **3.1 Skull**

The skull including the mandible of an adult male rhesus monkey is depicted in **Figure 7**. Some major anatomical landmarks are indicated. The splanchnocranium is relatively large but presents a reduced length. The very large conical orbits are almost completely postorbitally closed. The neurocranium is situated caudal to the former. It contains the cranial cavity that harbors the brains. The mandible and in particular its body is relatively large. A prominent mandibular angle can be seen. The symphysis between the left and right mandibles is synostotic.

The hyoid bone of the rhesus monkey (**Figure 8**) is not directly connected to the skull. It consists of a body (corpus) and a bilaterally present pair of horns that lie caudally. The lesser horn (cornu minus) is, however, fused with the greater horn (cornu majus). The latter horns are joined with the body by means of cartilage.

#### **Figure 6.**

*Skeleton of a female rhesus monkey. 1: cranium, 2: mandibula, 3: vertebrae cervicales, 4: scapula, 5: clavicula, 6: humerus, 7: radius, 8: ulna, 9: manus, 10: vertebrae thoracales, 11: sternum, 12: arcus costalis, 13: vertebrae lumbales, 14: sacrum, 15: pelvis, 16: femur, 17: patella, 18: tibia, 19: fibula, 20: pes, 21: vertebrae caudales.*

#### **Figure 7.**

*Left lateral view of the skull of an adult male rhesus monkey. The splanchnocranium and neurocranium are shaded in red and green, respectively. 1: orbita, 2: canalis lacrimalis, 3: foramen infraorbitale, 4: foramen zygomaticofaciale, 5: os nasale, 6: os incisivum, 7: maxilla, 8: os frontale, 9: os parietale, 10: arcus zygomaticus, 11: fossa temporalis, 12: porus acusticus externus, 13: processus styloideus, 14: crista nuchae, 15: linea temporalis, 16: planum nuchale, 17: foramen magnum. The mandible is shaded in purple. 18: angulus mandibulae, 19: processus condylaris, 20: processus coronoideus, 21: foramen mentale.*

*Anatomy of the Rhesus Monkey (*Macaca mulatta*): The Essentials for the Biomedical Researcher DOI: http://dx.doi.org/10.5772/intechopen.99067*

#### **Figure 8.**

*Dorsal view of the hyoid bone. The large corpus (1) is caudally elongated by the bilateral cornu minus (2) and the bilateral cornu majus (3) that are fused.*

#### **3.2 Axial skeleton**

The vertebral column consists of 7 cervical vertebrae, 12 thoracic vertebrae, 7 lumbar vertebrae, 3 fused sacral vertebrae and around 19 caudal vertebrae. This number is variable. The fifth, sixth and seventh caudal vertebrae possess a hemal arch that encloses the caudal artery and vein. The number of rib pairs equals the number of thoracic vertebrae, i.e. 12. Consequently, the rhesus monkey presents 24 ribs in total. These are connected to the sternum, which is composed of 7 sternebrae, by means of costal cartilages. The manubrium is the first sternebra to which not only the first pair of ribs is connected, but also the bilaterally present clavicle (**Figure 9**). This bone

#### **Figure 9.**

*Dorsal view of the sternum. 1: manubrium sterni, 2: corpus sterni, 3: sternebra, 4: processus xyphoideus, 5: incisura clavicularis, 6: incisura costalis, 7: clavicula.*

#### **Figure 10.**

*Lateral view of the right scapula. 1: margo dorsalis, 2: margo caudalis, 3: margo cranialis, 4: angulus cranialis, 5: angulus caudalis, 6: angulus ventralis, 7: spina scapulae, 8: fossa infraspinata, 9: fossa supraspinata, 10: acromium, 11: facies articularis clavicularis, 12: collum scapulae, 13: incisura scapulae, 14: cavitas glenoidalis, 15: tuberculum supraglenoidale, 16: tuberculum infraglenoidale, 17: processus coracoideus.*

#### **Figure 11.**

*Cranial (A) and caudal (B) views of the right humerus. 1: epiphysis proximalis or extremitas proximalis, 2: diaphysis or corpus humeri, 3: epiphysis distalis or extremitas distalis, 4: caput humeri, 5: collum humeri, 6: tuberculum majus, 7: tuberculum minus, 8: crista tuberculi minoris, 9: crista tuberculi majoris, 10: sulcus intertubercularis, 11: tuberositas deltoidea, 12: epicondylus lateralis, 13: epicondylus medialis, 14: fossa radialis, 15: fossa coronoidea, 16: trochlea humeri, 17: capitulum humeri, 18: fossa olecrani, 19: sulcus nervi radialis.*

*Anatomy of the Rhesus Monkey (*Macaca mulatta*): The Essentials for the Biomedical Researcher DOI: http://dx.doi.org/10.5772/intechopen.99067*

connects the sternum with the thoracic limb through its junction with the acromion of the shoulder blade.

### **3.3 Appendicular skeleton**

#### *3.3.1 Thoracic limb*

The thoracic limb, which is connected with the thorax by means of the clavicle, is composed of the shoulder blade or scapula (**Figure 10**), the humerus (**Figure 11**), the medially located radius (**Figure 12**) and the laterally located ulna (**Figure 13**) that are unfused, and the hand (**Figure 14**). The hand contains five fingers that are each composed of 3 phalanges, except the first, called the pollex, that lacks the middle phalanx.

#### **Figure 12.**

*Cranial (A) and caudal (B) views of the right radius. 1: epiphysis proximalis or extremitas proximalis, 2: diaphysis or corpus radii, 3: epiphysis distalis or extremitas distalis, 4: caput radii, 5: fovea articularis, 6: collum radii, 7: tuberositas radii, 8: processus styloideus radii, 9: facies articularis carpalis, 10: tuberositas pronatoria, 11: incisura ulnaris.*

#### **Figure 13.**

*Cranial (A) and caudal (B) views of the right ulna. 1: epiphysis proximalis or extremitas proximalis, 2: diaphysis or corpus ulnae, 3: epiphysis distalis or extremitas distalis, 4: olecranon with tuber olecrani, 5: incisura trochlearis with processus anconeus, 6: processus coronoideus medialis, 7: processus coronoideus lateralis, 8: tuberositas ulnae, 9: crista musculi supinatorii, 10: caput ulnae, 11: facies articularis, 12: processus styloideus ulnae.*

#### *3.3.2 Pelvic limb*

The pelvic limb connects to the body through the pelvis that consists of the fused left and right pelvic bones (**Figures 15** and **16**). The symphysis between these bones is synostotic. The femoral bone or femur presents a distal trochlea for the ovoid patella. Both femoral condyles, which each support a sesamoid bone on their caudoproximal aspects, articulate with the tibial plateau (**Figure 17**). The tibia (**Figure 18**) lies medial to the slender fibula (**Figure 19**). The foot (**Figure 20**) contains five toes that are each composed of 3 phalanges, except the first, called the hallux, that lacks the middle phalanx.
