This page looks at musculoskeletal structure and events that occur at late embryonic Carnegie stage 22.
Page Links: Axial Skeleton | Upper limb | Lower limb
The axial skeleton consists of: Skull, Auditory Ossicles, Hyoid bone, Vertebral column, Chest (sternum, ribs)
The vertebral column is a series of bone segments (vertebra) separated by specialized joints (intervertebral disc). In the adult, these vertebral elements are made up of rostro-caudally: 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, coccyx.
The axial skeleton is derived from mesoderm forming paraxial mesoderm forming somites from which part forms scleretomes forming vertebra and intervertebral discs (More? Molecular - Vertebral Column).
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D1,D2: Vertebral body (centrum). Head of rib. Lamina of vertebral arch. Transverse processes. Vertebral canal. Spinal cord. Dura. Intervertebral foramen containing dorsal root ganglion (now in a ventral position!). Ribs. Sympathetic ganglia. Costovertebral and costotransverse joints. Note that laminae of the arches have not fused dorsally but are united by a connective tissue membrane (dorsal uniting membrane or ligament) which provides the guide-path for the growth and subsequent fusion of the laminae. The dura constitutes the ventral uniting membrane or ligament. Part of intervertebral disc seen in D2. |
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D3: Ganglia in intervertebral foramina. Costovertebral joint. |
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D4: Anteriorly, note ribs joining the sternum and intercostal muscles
D4: Pedicle of vertebral arch. The dark, fibrous tissue at the anterior margin of the vertebral column is the intervertebral disc (derived from dark part of sclerotome). Note erector spinae group of muscles. |
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E4: Vertebral body with intervertebral disc ventrally. Notochord remnant at junction of body and intervertebral disc. |
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E6: Next vertebral body (notochord incorporated into cartilage). |
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F1: Mostly intervertebral disc with notochord remnant |
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F2: Transverse abdominal muscle, internal and external oblique abdominal muscle, rectus abdominis muscles. |
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F7,G1: (Lumbar cross-section). Vertebral body and I.V. disc. Psoas major muscle. Erector spinae muscles. Note short laminae of the arches and wide dorsal uniting ligament. |
Links: Molecular - Vertebral Column |
The appendicular skeleton consists of: Shoulder girdle, Upper limb (arm, hand), Pelvic girdle, Lower limb (leg, foot).
Lower limb (Row G) |
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G1: Knee mesenchyme |
G2: Patella. Femur. Flexor and extensor muscles. |
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G4: Knee joint. Tibia and femur. Hip bone: pubis, ischium, ilium, head of femur. Developing acetabulum. Adductor group of muscles. |
G5: Hip joint. Acetabulum. Head and greater trochanter of femur. Sacro-iliac joint. |
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G6: Heel. Ischium. Sacro-iliac joint. |
G7: Tarsal cartilages (note inverted position of feet). Heel. Phalangeal cartilages. |
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The mesoderm forms nearly all the connective tissues of the musculoskeletal system. Each tissue (cartilage, bone, and muscle) goes through many different mechanisms of differentiation.
These note therefore have many different pages covering each of tissue, as well as information about limb development. Use the left hand menu to go to a specific topic of interest.
Please email Dr Mark Hill if you wish to make a comment about this current project.
