The chondrocranium (or ''cartilaginous
neurocranium'') is the primitive
cartilaginous skeletal structure of the fetal
skull that grows to envelop the rapidly growing
embryonic
brain
The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...
.
[Salentijn, L. ''Biology of Mineralized Tissues: Prenatal Skull Development'', Columbia University College of Dental Medicine post-graduate dental lecture series, 2007]
The chondrocranium in different species can vary greatly, but in general it is made up of four components, the sphenoids, occipitals, otic capsules, and nasal capsules.
In
human
Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s, the chondrocranium begins forming at 28 days from
mesenchymal condensations and is fully formed between week 7 and 9 of fetal development. While the majority of the chondrocranium is succeeded by the bony skull, some components do persist into adulthood.
In
cartilaginous fishes (e.g.
shark
Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...
s and
rays) and
agnatha
Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...
ns (e.g.
lampreys and
hagfish
Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...
), the chondrocranium persists throughout life.
[Kent, G.C & Miller, L. (1997): Comparative Anatomy of the Vertebrates. Wm. C. Brown Publishers. .] Embryologically, the chondrocranium represents the basal cranial structure, and lays the base for the formation of the
endocranium.
Divisions
The portion of the chondrocranium that is associated with the
notochord
The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the verteb ...
is termed the chordal chondrocranium and is formed from
mesodermally-derived
mesenchyme. The more
rostral portion of the chondrocranium that lie anterior to the notochord constitutes the prechordal chondrocranium, and is derived primarily from
neural crest-derived mesenchyme.
See also
*
Dermal bone
References
Vertebrate developmental biology
Skull
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