Chapter 7: Cranial Skeleton Flashcards
Chondrocranium
Protects the brain and special sense organs,
Begins as cartilage that is partly or entirely replaced by bone,
Also called the neurocranium
- Cartilages grow and fuses together to produce the basic ethmoid, basal, and occipital regions
- Regions ossify to form bones and sensory capsules
In which vertebrates does the chondrocranium remain cartilaginous
Lampreys, hagfish - several cartilaginous components of the embryonic chondrocranium remain in adults as more or less independent cartilages
Cartilaginous fishes - retain a cartilaginous chondrocranium throughout
In which vertebrates does the chondrocranium get covered by membrane bone
Bony fishes, lungfishes, and most ganoids - retain highly cartilaginous chondrocranium that is covered by membrane bone
In which vertebrates does the chondrocranium become entirely replacement bone
Other bony vertebrates - embryonic cartilaginous chondrocranium is largely replaced by replacement bone (several ossification centers)
what are the 4 main ossification centers in this kind of skull for replacement bone?
- two for otic
- occipital
- sphenoid
Splanchocranium in tetrapods
highly modified to support the tongue and vocal apparatus
Splanchocranium in fish
a series of cartilaginous or bony arches in the wall of the pharynx, each arch lying between gill slits
Describe Development of Splanchocranium
Devloped by neural crest cells(makes mostly face)
During early embryonic development, neural crest cells contribute to the head mesenchyme (ectomesoderm)
Also contributing to the head mesenchyme are cells of mesodermal origin (mesodermal mesenchyme/aka embryonic connective tissue)
The position of the mesodermal (stippled) and the neural crest (shaded) mesenchyme, and the approximate interface between them
What are the 2 theories for the evolution of Jaws?
Serial theory
Composite theory
In both, mandibular arch makes up upper and lower jaw
Serial Theory
Early fish had several gill arches, which were bony or cartilaginous structures supporting the gills
Transformation: According to the serial theory, the first couple of these gill arches evolved into the upper and lower jaws. Specifically, the mandibular arch became the lower jaw (mandible), and the palatoquadrate became the upper jaw
Composite theory
The theory says that more than one gill arch contributed to the formation of the jaw structure
Elements from the mandibular, hyoid, and perhaps premandibular arches fused and modified over time. This fusion led to the complex structure we recognize as jaws today
The resulting jaw structure was more versatile and robust, capable of greater functionality, which gave early vertebrates a significant survival advantage.
What is a branchial basket? Which vertebrates have one?
The branchial basket, often called the gill basket, is a skeletal structure found in the pharyngeal region of certain vertebrates. It supports the gills and aids in respiration and feeding.
Seen in cartilaginous fish (sharks, rays) and lamprey/jawless fish
Branchial Arch I
(Mandibular Arch)
2 parts: palatoquadrate and Meckel’s cartilage
Branchial Arch II
(Hyoid Arch)
1 important bone, hyomadibula
Branchial Arches 3-7
Each arch has same 5 parts:
Pharyngobranchial
Epibranchial
Ceratobranchial
Hypobranchial
basibranchial
