Post-cranial Axial Skeleton Flashcards
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
Keystone of the vertebrate skeleton
Segmented, more or less flexible, arched rod flanked by axial musculature
Vertebral Column
Vertebral Column function
Suspends the trunk
Protects the spinal cord
Suspend the trunk
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
In many extinct amphibians and few amniotes with two centra, the more cranial is called an
intercentrum
In many extinct amphibians and few amniotes with two centra the more caudal is called a
pleurocentrum
Some extinct ________ only have the intercentrum while ________only have the pleurocentrum
amphibians
amniotes
Types of Vertebra Based on Centra
no centra
Aspondyly
Types of Vertebra Based on Centra
with only 1 centrum per segment
Monospondyly
Types of Vertebra Based on Centra
the single centrum (intercentrum) is separate
Stereospondyly
Types of Vertebra Based on Centra
with two centra per segment
Diplospondyly
Types of Vertebra Based on Centra
the approximate equal-sized centra are separate
Embolomerous
Types of Vertebra Based on Centra
with five to size centra per segment
Polyspondyly
Types of Vertebra Based on Centra
centra and spines are separate
Aspidospondyly
Types of Vertebra Based on Centra
with numerous separate parts that constitute each segment
Rachitimous
Types of Vertebra Based on Centra
centra and spines are fused into a single bone
Holospondyly
Types of Vertebra Based on Centra
with husk-shaped centrum usually pierced by a notochordal canal
Lepospondyly
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
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
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
Types of Centra Based on Shape
flat ended
Can withstand compression and limit motion
Characteristic of mammals
Acoelus/amphiplatyan
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
arches
this and the interconnecting ligaments enclose a long vertebral canal which is occupied by the spinal cord
Neural arches
arches
are inverted beneath the centra of tail and houses the caudal vessels
Hemal arches
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
25
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
