28Development of the diaphragm Muscle: from C4 myotome (phrenic nerve!)Development: innervation shows the origin…
29Development of the skull The development of the skull- Viscerocranium (Splanchnocranium = visceral skull, facial skeleton)- Neurocranium (around the brain)Bones can develop by- enchondral ossification (base of skull + some facial bones): chondrocraniumintramembranous (calvaria + mandible, maxilla etc.): desmocraniumSources: the embryonic tissue around the developing brain:The first 4 occipital somites lat. parts of occipital bonenon-segmented paraxial mesoderm: somitomeres base of the skull (partly)neural crest (ecto-mesenchyme) first two branchial arches (gill arch in fish) splanchnocranium (facial skeleton), bones of calvariaDevelopment of the skull+ structures from branchial arches I-II.
30The development of the skull - Viscerocranium (Splanchnocranium = visceral skull, facial skeleton)- Neurocranium (around the brain)Bones can develop by- enchondral ossification (base of skull + some facial bones)intramembranous (calvaria + mandible, maxilla etc.)Sources: the embryonic tissue around the developing brain:The first 4 occipital somites lat. parts of occipital bonenon-segmented paraxial mesoderm: somitomeres base of the skull (partly)neural crest (ecto-mesenchyme) first two branchial arches (gill arch in fish) splanchnocranium (facial skeleton), bones of calvariaPrechordal or
31- at the base of the skull and - at the face (from the nasal capsule). Chondrocranium - enchondral ossification: cartilage model turns into bone- at the base of the skull and- at the face (from the nasal capsule).The base of the skull: occipital bone (except upper part of its squama), petrous part of temporal (around the ectodermal acoustic placod -organ of hearing), sphenoid: body, wings and lateral (!) plates of pterygoid process.The nasal capsule ethmoid, inferior nasal concha.The remaining parts of the cartilaginous nasal capsule give the nasal cartilages which persist in adults.+ structures from branchial arches I-II.
32Desmocranium - intramembranous ossification: from the connective tissue covering of the developing brain. The first centers of ossification: tuber frontalia and parietalia ossification of the connective tissue spreads radially.Calvaria: frontal, parietal, squamous part of temporal, tympanic part of temporal bones.On the face: nasal, lacrimal, maxilla, zygomatic, vomer, palatine; medial plate of pterygoid process. Mandible also, but it develops from branchial arch.+ structures from branchial arches I-II.
33The splanchnocranium originally develops from the first and second branchial arches. 1. The first (or mandibular) branchial arch contains the Meckel's cartilage.The Meckel's cartilage in the cartilaginous fish is an ancient form of the jaw which articulates with the cartilagineous part of temporal bone.The posterior part of the Meckel’s cartilage is transformed into the malleus and incus (2 auditory ossicles, the hammer and the anvil). Around (!) the Meckel’s cartilage model: the mandible is ossified via intramembranous ossification.2. The second (or hyoid) branchial arch contains the Reichert's cartilage.The derivatives: the upper part of the hyoid bone*, the styloid process* and the stapes (the third auditory ossicle, the stirrups).(*Between them the mesechyme forms the stylo-hyoid ligament.)
35Which type of ossification? Where there is no clear ’model’ (shape) for a body area yet and an expansive development of the body part is needed (e.g. limbs, face): first cartilage appears, later enchondral ossification will generate the model for the body part.Where there is a pre-existing organ with well defined shape and it has an ability for expansive growth (e.g. the brain!), it is enough to ossify its connective tissue capsule (=intramembranous ossification).Malformations:Problems with the endochondral ossification: chondrodystrophia results in a serious problem in limb longitudinal growth and chondral skull bone growth dwarfs with depressed nasal root and huge, balloon-like neurocranium and very prominent facial bones.Problems with the intramembranous ossification: the calvaria of the skull and the clavicle are poorly developed (dysostosis cleidocranialis).