The role of soft tissues in skull growth in rabbits

ABSTRACT

The vault is said to expand centrifugally, following expansion of the brain or of an equivalent fluid mass. The bones are carried passively outwards. However, the frontal bone shows, simultaneously, sutural growth resorption in parasutural areas endocranially and in the olfactory fossa stasis or slow erosion ectocranially over the eminence, differential endocranial and estocranial deposition, and differential deposition and resorption on the orbital plate; and a pronounced postolfactory ridge of endocranial deposition. Cartilage is said to act as "pacemaker", its interstitial growth and turgidity enabling it to thrust bones in particular directions. Pressure on bone familarly leads to resorption. Two areas on the frontal bone in contact with the enlarging cartilaginous ethmoid show, respectively, resorption and deposition. The response to thrust is not simple. Can muscular pressure affect the form of the braincase? The squamosal bone forms a bed for muscles (1) the temporalis (a) attached to its postzygomatic surface above, fibres nearly horizontal (b) attached to its orbital surface, fibres vertical; (c) its tendon related to the upper aspect of the zygomatic process root; and (2) the lateral pterygoid related to the paracondylax fossa and inferior margin. Surface (1) (a) shows deposition; (1) (b) marked resorption; (1) (c) shows stasis early, slow deposition later - a rate of deposition increased by temporalis section. Surface (2) shows resorption above, with continuous osseous drift inwards, and below, deposition. Further experiments are needed to elucidate the cause-effect relationships between muscle and bone. The contribution of the sense capsules to the overall form of the cranium has been neglected. The cribriform plate is displaced endocranially, as is the posterior part of the orbit, where it forms neurocranial wall. The circumferential growth of the ear capsule causes periotic encroachment upon the cranial cavity. Thus brain growth must be compensated for at areas other than these (AU)