Post-cranial Axial Skeleton Flashcards by Miyaki Jan Lim

The primitive axial skeleton, replaced by the vertebral column

Unsegmented and composed of dense fibrous connective tissue

The first skeletal element to appear in the embryo of chordates

Notochord

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Keystone of the vertebrate skeleton

Segmented, more or less flexible, arched rod flanked by axial musculature

Vertebral Column

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Vertebral Column function

Suspends the trunk
Protects the spinal cord
Suspend the trunk

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Principal part of the vertebra which lies just below the spinal cord where it surrounds, restricts or replaces the notochord

May consist of one or two elements

Centrum

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In many extinct amphibians and few amniotes with two centra, the more cranial is called an

intercentrum

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In many extinct amphibians and few amniotes with two centra the more caudal is called a

pleurocentrum

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Some extinct ________ only have the intercentrum while ________only have the pleurocentrum

amphibians
amniotes

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Types of Vertebra Based on Centra
no centra

Aspondyly

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Types of Vertebra Based on Centra
with only 1 centrum per segment

Monospondyly

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Types of Vertebra Based on Centra
the single centrum (intercentrum) is separate

Stereospondyly

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Types of Vertebra Based on Centra
with two centra per segment

Diplospondyly

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Types of Vertebra Based on Centra
the approximate equal-sized centra are separate

Embolomerous

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Types of Vertebra Based on Centra
with five to size centra per segment

Polyspondyly

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Types of Vertebra Based on Centra
centra and spines are separate

Aspidospondyly

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Types of Vertebra Based on Centra
with numerous separate parts that constitute each segment

Rachitimous

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Types of Vertebra Based on Centra
centra and spines are fused into a single bone

Holospondyly

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Types of Vertebra Based on Centra
with husk-shaped centrum usually pierced by a notochordal canal

Lepospondyly

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Types of Centra Based on Shape
concave at both ends
Limited motion is permitted in any direction
Characteristic of most fishes, some salamanders and caecilians

Amphicoelus

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Types of Centra Based on Shape
convex in front and concave in back
Permit motion in any direction
Characteristic of most salamanders and chelonians

Opisthocoelus

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Types of Centra Based on Shape
concave in front and convex in back
Permit motion in any direction
Characteristic of anurans and modern reptiles

Procoelus

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Types of Centra Based on Shape
flat ended
Can withstand compression and limit motion
Characteristic of mammals

Acoelus/amphiplatyan

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Types of Centra Based on Shape
saddle-shaped Allow vertical and lateral flexion but prevent rotation around the axis of the spine
Characteristic of birds

Heterocoelus

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arches
this and the interconnecting ligaments enclose a long vertebral canal which is occupied by the spinal cord

Neural arches

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arches
are inverted beneath the centra of tail and houses the caudal vessels

Hemal arches

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Processes or Apophyses are the most common articulating with the ribs and serves as attachment for muscles

Diapophyses (transverse processes)

Processes or Apophyses can be prezygapophyses or postzygapophyses

Zygapophyses

Processes or Apophyses are lateral projections from the centra of a few tetrapods and serve as articulation site for bicipital rib

Parapophyses

Processes or Apophyses are prominent midventral projections from the centra of snakes and few other amniotes

Hypapophyses

Processes or Apophyses are paired ventrolateral processes which are remnants of the hemal arch bases that may receive articulation with ventral ribs

Basopophyses

Processes or Apophyses are transverse processes fused with remnants of ribs in the cervical and lumbar regions

Pleurapophyses

Mesenchymal cells from sclerotomes surround the notochord and neural tube and produce the _______ for future vertebra

blastema

________ deposit a cartilaginous central and neural or hemal arch

Chondroblasts

Membrane bone is deposited in teleosts, urodeles and apodans but arches arise from _________

cartilage

Cartilage is generally replaced by bone except in _________

chondrichthyans

is formed by deposition of cartilage in the sheath and notochord itself in many fishes, urodeles and apodans

Chordal cartilage

orders that consist of perichordal membrane bone, chordal cartilage and unaltered notochordal tissue

Urodeles and apodans

order that has a replacement bone deposited in a perichordal blastema and the notochord disappears

Anurans

Centra is formed by ___________ from the caudal half of one somite and the cranial half of the succeeding one and establishing a perichordal blastema around the notochord

scleroblasts

___________ are typically intersegmental and myomeres are segmental

Centra

is a condition in which there are 2 centra per segment located in the tail and is characteristic of some fishes Increased flexibility for locomotion

Diplospondyly

fish exhibits only two major morphologic regions:

Trunk (dorsals) Tail (caudals)

animals that have Notochord is prominent Only skeletal elements are lateral neural cartilages Limited to the tail region in hagfishes Caudally, they fuse to form a single longitudinally dorsolateral cartilaginous plate perforated by foramina for spinal nerves Some scientists consider them as fused fin support

Agnathans

animals that have Notochord is present throughout the length of the adult vertebral column and is constricted within each centrum Centra is composed of chordal and perichordal cartilage and is amphicoelus Vertebral canal consists of paired dorsal plates, paired dorsal intercalary plates and supradorsal cartilages in other species Neural arches and intercalary plates are perforated by foramina for the dorsal and ventral roots of spinal nerves and blood vessels Hemal arches consist of ventral plates Ventral intercalary plates are common Fibroelastic ligament overlies and connects the neural spines along the entire length of the vertebral column

Chondrichthyans

animals that have Consisted of calcified rings of cartilages that had been deposited in the notochord sheath Rings were more numerous than the body segments

Extinct Holocephalan

animals that have Well-ossified amphicoelus vertebrae Centrum is dumb-bell shaped vacuole where the notochord previously existed Space between successive vertebrae is occupied by porous cartilage-like material Centra and neural arches are interconnected by a complex system of collagenous and elastic ligaments Neural spines are often very tall and are sometimes surmounted by supraneural bones Variety of processes usually unique to fishes protrude from the arches and centra

Actinopterygians

animals that have Dipnoans, chondrostei and coelocanth develop no centra Notochord is present and unconstricted and its thick sheath contains little cartilage or bone Basidorsal, basiventral, interdorsal and intervertebral cartilages are associated with the notochord Dipnoans, chondrostei and coelocanth develop no centra Notochord is present and unconstricted and its thick sheath contains little cartilage or bone Basidorsal, basiventral, interdorsal and intervertebral cartilages are associated with the notochord

Sarcopterygians

animals that have Have two centra and two sets of neural and hemal arches in each metamere of the tail Diplospondylous condition in which the centra is double the number of myomeres and spinal nerves

Elasmobranchs and Other Bony Fishes

Rhipidistian and early labyrinthodonts consisted of several bones per segment median, U-shaped anterior bone that cradled the notochord

Hypocentrum

Rhipidistian and early labyrinthodonts consisted of several bones per segment small wedges of bone overlying the notochord dorsolaterally

Pleurocentra

Rhipidistian and early labyrinthodonts consisted of several bones per segment Left and right laminae of bone lateral to the spinal cord the collectively provides a ______

neural arch

Rhipidistian and early labyrinthodonts consisted of several bones per segment Notochord is _________ throughout the body but is constricted at the level of the hypocentrum

continuous

Evolution of Tetrapod Vertebrae large intercentrum and a small pleurocentra

Rhachitomi

Evolution of Tetrapod Vertebrae retained only the intercentrum

Stereospondyli

Evolution of Tetrapod Vertebrae increased the size of the pleurocentrum to the size of the intercentrum

Embolomeri

Evolution of Tetrapod Vertebrae enlarged pleurocentrum to near or complete exclusion of intercentrum

Amniotes

Tetrapod vertebrae except urodeles and apodans appear to be modifications of ______________ Increased size of pleurocentrum and decreased size of hypocentra

rachitimous vertebrae

Evolution of Tetrapod Vertebrae Modern adult tetrapod vertebra is a composite structure Centrum begins ossification at several paired and median loci in the ____________

perichondral blastema

Development of mobile joint between the first vertebra and the skull Shortening or eliminating ribs of more cranial vertebrae Increasing mobility of intervertebral joints

Cervical vertebra

Presence of long ribs in the anterior portion of the trunk

Thoracic vertebra

Immediately after the thoracic Supports the abdominal cavity

Lumbar vertebra

Supports the stress transmitted to the pelvic girdle

Sacral vertebra

Tail vertebra

Caudal vertebra

class that have: Single cervical vertebra Lacks processes and bears facets for articulation with the occipital condyles Permits limited rocking of the skull not available in fishes

Amphibians

Cervical Vertebra of Amniotes Ringlike because its centrum is missing Has facets for articulation with the occipital condyles Centrum became the odontoid process of the axis - held in place by transverse atlantal ligament Reduction or absence of zygapophyses on results to rocking of the skull and atlas Sphenodon chondrifies and unites with axis just before hatching

Atlas

Cervical Vertebra of Amniotes Resembles a neural arch and is derived from a pair of bilateral cartilaginous blastemas Found in crocodilians, Sphenodon and insectivorous spiny hedgehogs Some modern lizards have a fibrous membrane instead of a bone

Proatlas

Cervical Vertebra of ________ Ball-and-socket joints allows the entire head and neck to be completely retracted in the shell Have only 8 cervical vertebrae

Turtles

Cervical Vertebra of ________ Exceptional flexibility due to the configuration of the vertebra (heterocoelus) Right-left convexity Dorsoventral concavity Increased number of cervical vertebra Commonly 12

Birds

swans number of Cervical Vertebra

Cervical Vertebra of __________ Almost always have 7 cervical vertebrae Length of centra and not the number determines the length in mammals

Mammals

Three edentates (two sloths and the great anteater) number of Cervical Vertebra Manatees number of Cervical Vertebra

Three edentates (two sloths and the great anteater) - 6, 8 or 9 Manatees - 6

animals with Sacral Vertebrae that are stout transverse process strong enough to bear the thrust of the pelvic girdles

Bears

class with 1 Sacral Vertebrae

Amphibians

classes with 2 Sacral Vertebrae

Living reptiles including most birds and opossums have 2

class with 3 to 5 Sacral Vertebrae

Most mammals have 3 to 5 (ankylosed)

Perissodactyls number of Cervical Vertebra Edentates number of Cervical Vertebra

Perissodactyls can have up to 8 Edentates can have up to 13

Fusion of the last thoracic, all lumbars and sacral and the first few caudals with the pelvic girdle Provides rigid brace for the teeter-totterlike stance of birds Little flexibility in the avian backbone caudal to the neck

Synsacrum

___________ have a synsacrum of up to 13 fused sacrals and caudals

Armadillos

Early tetrapods usually numbered 50 or more Reduced and dictates how the tail is used in modern mammals Processes and arches become progressively shorter and rudimentary towards the end until such that the last segment is a small cylindrical centra

Caudal Vertebrae

Found in anurans that develops from continuous elongated perichordal cartilage at the base of the tail Composed of post-sacral vertebrae

Urostyle

Responsible for the regeneration of the tail of many lizards especially when caught

Autotomy

Fusion of usually the last caudals which becomes the skeleton of the visible tail of birds

Pygostyle

Rudimentary but with transverse processes and lack arches Diminished in size and usually fused in apes and humans Recurrent tailbone soreness in people who have had an earlier fall in their life

Coccyx

Articulate with vertebrae and extend into the body wall Formed intersegmentally by scleroblasts from two successive mesodermal somites like the centra

Ribs

___________ ribs of some reptiles are not ribs but remnants of dermal exoskeleton

Abdominal ribs or gastralia

Basal actinopterygians and some teleosts have ________ sets of ribs associated with each vertebra

two

in fish (ribs) pass laterad into the horizontal skeletogenous septum that separates the epaxial and hypaxial muscles

Dorsal ribs

in fish (ribs) develop in myosepta and arch ventrad in the lateral body wall just external to the parietal peritoneum Approach one another to form hemal arches commencing at the vent

Ventral ribs

Some fishes have only __________ (except perch) and some have only dorsal ribs (_________)

ventral ribs sharks

animals that Ribs were associated with vertebrae from the atlas to nearly the base of the tail in early tetrapods Became restricted in number and the short ones ankylosing Longs ribs of the anterior thoracic region acquired anchorage (sternum) Occupy the same position as of the ventral ribs of fishes and they encircle the coelomic cavity They are however not homologous Ribs of tetrapods are homologous with the dorsal ribs of fishes Most ribs are bicipital having a dorsal tuberculum (transverse process) and a ventral capitulum (hypocentrum)

Tetrapods

Articulation of capitulum varies in different modern tetrapods:

Two adjacent demifacets (half-facets) Parapophysis if present Facet on a single centrum

Other _________ have the tuberculum reduced in size of others have fusion of tuberculum and capitulum (crocodilians) and tuberculum remaining

tetrapods

Tetrapods Thoracic ribs have two parts: __________ribs are those that adjacent to the vertebrae and ___________ ribs are more ventral and articulates with the sternum

costal sternal

Tetrapods Sternal ribs may remain cartilaginous (humans) and are called

costal cartilages

animals that Very short in anurans and urodeles Ankylosed to transverse process in anurans Ribs of the burrow-dwelling apodans are long Only the ribs of anurans are not bicipital

Amphibians

Nonavian Reptiles that have long ribs on many of the trunk vertebrae and short ribs in most of the neck

Lizards and crocodilians

Nonavian Reptiles that have long ribs on many of the trunk vertebrae and short ribs in most of the neck

Sphenodon

Nonavian Reptiles that have ribs with every cervical vertebra More specialized ________ usually lack them on the atlas and axis

Geckos

Nonavian Reptiles Half dozen or more of the posterior ribs are elongated Can be rotated outward to elevate the patagium

Draco

Nonavian Reptiles Have no cervical ribs and trunk ribs are fused with costal plates Sacral ribs are not fused with the carapace and are short with the expanded distal ends ankylosed to the ilium

Turtles

Nonavian Reptiles Long, curved ribs beginning at the second vertebra and continuing to the tail No sternum for rib attachment but ventral ends of ribs have ligamentous connections with integumentary scutes Long, curved ribs in cobras can be rotated outward causing a fold of loose skin to spread and is inflated with air from the lungs

Snakes

animals that have First two pairs or ribs articulate with the last two cervical vertebrae at the base of the neck in carinates that are generally movable and lack a sternal segment Next 5 pairs are thoracic ribs that are thin, flat and broad and have uncinate processes in most Caudal ribs are ankylosed to the synsacrum

Birds

animals that have Generally confined in the thorax Ranges from 9 pairs (whales) to 24 pairs (sloths) with 12 being most common If more than 10 ribs are present, all that remain are floating or are not connected with the sternum Transverse foramen is created from the fusion of the transverse process and the centra

Mammals

Only a tetrapod structure and predominantly found in amniotes and is of endochondral in origin Presence, size and anatomical relationships are correlated with the extent to which the forelimbs are employed in locomotion

Sternum

Sternum Functions:

Base against which the pectoral girdles and ribs are braced Anatomical origin of ventral muscles of the forelimb

the bone that is the Largest in animals that fly and is reduced or absent in tetrapods lacking forelimbs

Sternum

the bone that Arises as paired mesenchymal bars that later unite and undergo chondrogenesis

Sternum

Presternal and suprasternal blastemas also develop in many

mammals

Presternal blastemas contribute to the formation of the _____ and ______

manubrium and suprasternal ossicles

__________ Only well differentiated in anurans

sternum

animals in amphibians that has more or less isolated nodules of cartilage associated with the linea alba caudal to the coracoid cartilages of the pectoral girdle Sternal element is present in other salamanders at the same location

Necturus

amphibians that have no trace of a sternum

Apodans

Nonavian Reptiles which are agile climbers and rubbers have a large shield-shaped sternum or cartilage or replacement bone

Lizards

Nonavian Reptiles have a simple cartilaginous plate attached to the procoracoid of the pectoral girdle continuing caudally in mineralized fibrous membrane incorporating the gastralia

Crocodilians

Nonavian Reptiles have no sternum

Turtles

class that have Sterna that is powerful and used for flight have developed an enormous keel or carina to which flight muscles are attached

Birds

class that have Composed of series of bony segments or sternebrae Last sternebrae or the xiphisternum bears a cartilaginous or bony xiphoid process

Mammals

type of mammals that have short sternum, only a few ribs reaching it and individual sternebrae tend to fuse

Marine mammals