HUMAN ANATOMY ATLAS - G.L. Bilich - 2014

THE LOCOMOTOR SYSTEM

THE SKELETAL SYSTEM

BONES OF THE SKULL

Ossification of the Skull Bones

The BONES OF THE skull develop from mesenchyme in two ways (Table 10):

✵ Directly from mesenchyme — direct osteogenesis — forming the bones of the cranial vault and facial Skeleton. They pass through two stages: membranous (Connective Tissue) and bony;

✵ With intermediate Cartilage formation — indirect osteogenesis, or endochondral ossification — forming the bones of the skull base. In this process, they pass through three stages: membranous (connective tissue), cartilaginous, and bony.

Elements formed through Direct and Indirect osteogenesis (desmocranium and chondrocranium) can fuse into a single bone (occipital, temporal, and sphenoid bones). The clavicle is the only tubular bone formed via direct osteogenesis; consequently, congenital defects in direct osteogenesis simultaneously affect both the skull bones and the clavicle.

The facial skeleton lies inferior to the neurocranium. A significant part of the facial skeleton is occupied by the Skeleton of the masticatory apparatus. This includes the paired Maxilla, as well as the Mandible, which articulates movably with the skull. The remaining bones of the facial region are small in size, contribute to the walls of the orbital, nasal, and oral cavities, and determine facial configuration. Some skull bones contain air-filled cavities that communicate with the Nasal cavity. Pneumatization of these bones reduces skull weight while maintaining structural strength. These cavities also act as voice resonators. A special place is occupied by the Hyoid bone, located in the anterior neck region and connected to the skull bones by Ligaments and Muscles.

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Fig. 42. Bones of the neurocranium (grey) and facial skeleton (blue), lateral view, right side

Fig. 43. Ossification of the neurocranium bones, lateral view, right side (endochondral — blue, endesmal — grey)

Table 9. Bones of the Neurocranium and Facial Skeleton

Table 10. Bones of the Desmocranium and Chondrocranium

Fig. 44. Frontal bone (A — external view, B — internal view):

1 — Frontal notch/foramen; 2 — Zygomatic process; 3 — Supra-orbital notch/foramen; 4 — Temporal line; 5 — Temporal surface; 6 — Superciliary arch; 7 — Glabella; 8 — Frontal suture; Metopic suture; 9 — External surface; 10 — Squamous part; 11 — Parietal margin; 12 — Frontal tuber; Frontal eminence; 13 — Supra-orbital margin; 14 — Nasal part; 15 — Nasal spine; 16 — Foramen caecum; 17 — Orbital part; 18 — Impressions of cerebral gyri; 19 — Grooves for Arteries; 20 — Frontal crest; 21 — Internal surface; 22 — Groove for superior sagittal sinus