Development of the
Skeletal System
EMBRYOLOGY: Note #1.
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1.
DEVELOPMENT OF THE SKELETAL SYSTEM
Development of the Skeletal System
Medical Editor: Jan Camille Santico
OUTLINE
I) SKULL
II) TRUNK
III) LIMBS
IV) INTRAMEMBRANOUS VS ENDOCHONDRAL
V) REVIEW QUESTIONS
VI) REFRENCES
I) SKULL
In the development of the skeletal system, there are two
primary goals:
o Form the
axial skeleton (skull, thoracic cage)
o Form the
appendicular skeleton (limbs)
The skull develops from
mesoderm and
neural crest
cells
(A) NEUROCRANIUM
The neurocranium is the
part of the skull which
encases/surrounds the brain
Recall: Trilaminar disc
o Superior to
the neural tube are neural crest cells
o Flanking the neural tube are
somites, which develop
from the segmentation of the paraxial mesoderm
The
occipital somites (located towards the cranial end
of the embryo) and the
neural crest cells migrate
cranially to from the
neurocranium
The neurocranium can be divided into three regions:
o Posterior cranial fossa
o Middle cranial fossa
o Anterior cranial fossa
The neurocranium can be divided into two types
based on
the process of bone formation:
o Chondrocranium
o Membranous neurocranium
(1) Chondrocranium / “Base of the Skull”
This part of the neurocranium is developed through
endochondral ossification
o Most bones are developed through this process
o The mesenchymal cells (of the paraxial mesoderm)
differentiate into chondrocytes first before
differentiating into osteoblasts
o Mesenchymal cell chondrocytes osteoblasts
The base of the skull is made up of the following bones:
o Occipital bone
o Petrous
part of temporal bone
o Sphenoid bone
o Ethmoid bone
Figure 1. Development of the Chondrocranium
