University:
University of Phoenix
Course:
BIO 101T | Principles of Biology 3
Academic year:

2024
Views:

712

Pages:

5
Author:

reitheadhtgr

Jaw Suspensorium Jaw suspension refers to the attachment of the upper and lower jaw with the skull. It primarily aids in biting and chewing. This attachment depends on the modification of visceral arches in vertebrates. There are five main types of jaw suspension: Autodiastylic Amphistylic Hyostylic Autostylic Craniostylic 1. Autodiastylic The jaws are attached to the cranium by anterior and posterior ligaments. The hyoid arch remains completely free or independent and doesn’t support the jaw. Gill cleft is present in front of the hyoid arch. Example: Early gnathostomes like acanthodians. 2. Amphistylic The quadrate or the basal and otic process of the upper jaw are attached by ligaments to the chondrocranium. The upper end of the hyomandibula is also attached to the chondrocranium. The two jaws are supported from each other, making a double suspension called amphistylic. Example: Found in crossopterygians and some primitive sharks. 3. Hyostylic Upper jaw is loosely attached by anterior ethmopalatin to cranium. Both jaws are stronger against the hyomandibular, which bites into the auditory region of the skull. The hyoid arch binds the two jaws together and to the cranium. Helps in enlarging the gape during swallowing larger prey. Example: Found in elasmobranchs and most bony fishes. 4. Autostylic Hyomandibula does not participate but is modified into stapes, transmitting sound waves. Upper jaw is directly and intimately bound to the cranium. Sub-types: Holostylic: Upper jaw fused with attached skull. Example: Lungfish, Holocephali. Monimostylic: Lower jaw suspended directly off the skull. Example: Many tetrapods. Streptostylic: Quadrate is movable and flexible. Example: Some reptiles like lizards, snakes, birds. 5. Craniostylic The squamosal, stapes (hyomandibular), incus (quadrate), and malleus (articular) articulate with the hyoid arch and dentary. Example: Present in mammals where the lower jaw articulates with the squamosal of the skull.