ANAT30007 Lecture Notes - Lecture 31: Foramen Magnum, Vertebral Column, Quadrupedalism
10 Jun 2018
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Nuchal muscles maintain stability of head - stronger, thicker and more numerous in apes
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Omocervacalis muscle in apes: from C1 to clavicle, deep to trapezius
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Rhomboids starts at nuchal line in apes (vs. T1-5 in humans)
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Biomechanical Considerations
Skull is a first order lever: fulcrum at foramen magnum. Nuchal muscles exert effort to keep
skull upright against its weight - hence apes require larger muscles to balance larger weight
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Pivot in apes is oblique and posterior
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Angle between Frankfurt Horizontal and the line that connects anterior-most part of
face (nose in humans, teeth in apes)
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Slightly more than 90° in humans, much larger in apes
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Basicranial flexion
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Much larger cerebrum and brain case, reduced masticator muscles, smaller jaw, non-
projecting canines
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Face pushed inwards
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Thorax
Deep and narrow rib cage - good for
quadrupedal (parasagittal) locomotion
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Vertebral column on outer edge. Centre of
Monkey:
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Locomotor Page 8
Clavicular length correlates with brachiation in primates
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Clavicle keeps shoulder above head in quadrupeds
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Vertebral column on outer edge. Centre of
gravity between 4 legs
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Scapula on side of rib cage to orient glenoid
ventrally - parasagittal movement only
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Shorter in quadrupeds
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Vertebral column closer to centre to bring
centre of gravity to midline
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Scapula is posterior, orients glenoid
laterally - greater mobility
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Clavicle longer in humans, even longer clavicle
in brachiators
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Broad and wide rib cage in apes and humans -
related to upright posture
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Difference between apes and humans
Locomotor Page 9
Document Summary
Nuchal muscles maintain stability of head - stronger, thicker and more numerous in apes. Omocervacalis muscle in apes: from c1 to clavicle, deep to trapezius. Rhomboids starts at nuchal line in apes (vs. t1-5 in humans) Skull is a first order lever: fulcrum at foramen magnum. Nuchal muscles exert effort to keep skull upright against its weight - hence apes require larger muscles to balance larger weight. Angle between frankfurt horizontal and the line that connects anterior-most part of face (nose in humans, teeth in apes) Slightly more than 90 in humans, much larger in apes. Much larger cerebrum and brain case, reduced masticator muscles, smaller jaw, non- projecting canines. Deep and narrow rib cage - good for quadrupedal (parasagittal) locomotion. Scapula on side of rib cage to orient glenoid ventrally - parasagittal movement only. Broad and wide rib cage in apes and humans - related to upright posture.
