Comparative Anatomy Study Guide, Exam II


Synarthroses - immovable joints: skull sutures
Amphiarthrosis - slightly movable joints: intervertebral joints
Diarthrodial - freely movable joints = synovial joints.
Synovial joint - joint capsule, fibrous capsule and synovial membrane, synovial fluid, hyaline
     cartilage, reinforcing ligaments.

The Skeleton: Cranium.
Three primary moieties:
1. Dermatocranium - skull roofing bones (dermal portions)
2. Chondrocranium - braincase (endochondral portions)
3. Splanchnocranium - visceral arches

 Skull development - know chondrocrianium developmental pattern.
 Know which bones are derived from the chondrocranium, which from dermatocranium,
     which from splanchnocranium.

Evolution of the Cranium.
Primitive agnathans: Ostracoderms - heavy, external, armor plates covered head and anterior body.
Extant agnathans - skeleton degenerate, cartilaginous elements only. Splanchnocranium external
        to branchial basket.
Chondrichthyes - skeleton also degenerate. Cartilaginous elements only.  Chondrocranium well
      developed, roofed over dorsally. Splanchnocranial elements deep to gill chambers.

Jaws present: palatoquadrate & meckel's cartilages apparently derived from first gill arch.

- well developed dermatocrania.  Homology of individual elements not always clear in
        derived forms.
Gill chamber covered by a single, bony operculum in osteichthyes.

- Braincase divided into two separate portions that are movably articulated (cranial
Posterior end of braincase penetrated by notochord.
Pineal foramen present between parietals.
Palatal bones invested with labyrinthodont teeth.
Postorbital portion of skull elongate, preorbital portion short.

Dipnoi (lungfishes) – braincase remains largely cartilaginous, dermal roofing bones reduced. Maxillae
     and premaxillae lost in modern forms.
Crushing palatal tooth plates.
No intracranial hinge joint.

Tetrapods – Skulls of earliest amphibians similar to those of advanced rhipidistians:
Homologous roofing bones present, 2) Pineal foramen present, 3) labyrinthodont teeth present, 4) Intracranial joint present, 5) posterior portion of cranium penetrated by notochord, 6) Clear homologies between bones of palate.
Differences from rhipidisians: Preorbital skull elongate, postorbital skull shortened.

– extensive loss of skull bones and fenestration of skull.
Much of chondrocranium persistently cartilaginous in frogs and salamanders.
Occipital condyles paired.

– Primitive skull similar to that of labyrinthodont amphibians except: less flattened, eyes laterally directed (dorsally directed in labyrinthodonts), snout region reduced in length.
Intertemporal, supratemporal, tabular and postparietal. bones lost from posterior skull table.

Amniote skulls classified on basis of temporal openings:
Anapsida – temporal fenestrae absent: Turtles.
Diapsida – two temporal fenestrae, one dorsal, one ventral: Archosaurs and Lepidosaurs.
Synapsida – only the lower temporal fenestra is present: Pelycosaurs, Therapsids, Mammals.
“Euryapsida” – probably modified diapsids, only upper temporal fenestra present: Plesiosaurs
   and Ichthyosaurs.

Pelycosaurs have single occipital condyle, expanded epipterygoid.
have double occipital condyle, secondary palate develops, dentary bone increases in size until
     other bones are all displaced.

– complete secondary palate: premaxillae, maxillae and palatines contribute.
Epipterygoid becomes alisphenoid
Temporal bone formed from squamosal, Petrous portion (prootic + opisthotic), and tympanic
Supraoccipital, exoccipitals, and basioccipital fuse to form occipital bone
Squamosal-dentary articulation completed
Angular becomes tympanic bone, columella becomes stapes, articular becomes malleus, and
quadrate becomes incus.
Parietals and frontals grow downward and inward below old skull roof to complete sides of

Diapsida – single occipital condyle
Lepidosaurs primitively have full complement of temporal arches and fenestrae
Lizards lose lower temporal arch and fenestra.
Snakes have lost both temporal arches and fenestrae, braincase enclosed by downgrowth of frontals and parietals. Skull becomes highly kinetic.

 Archosauria – skull heavily armored in crocodilia, no kinesis.
Mandible fenestrated.
Skull pneumatized with a series of interconnecting channels.
Snout fenestrated in many forms, e.g. dinosaurs.


Squamosal – postorbital bar lost
Braincase closed by a dermal laterosphenoid
Teeth lost entirely, functionally replaced by beak (as in turtles)
Single occipital condyle
Enlarge orbit: sclerotic ossicles present (as in some other reptiles)
Enlarged premaxilla
Skull kinetic w/ hinge joint at nasofrontal suture and independently mobile quadrates and bony
Pneumatized skull.

Jaw Suspension

Paleostylic - No visceral arch involvement: agnatha
Euautostylic – Mandibular arch alone suspended from skull: placoderms and acanthodians

Amphistylic – Two articulation points: 1) Palatoquadrate to skull, 2) hyomandibular arch to
    skull: Early sharks, some osteichthyes, crossopterygians.  Modern sharks have modified
    amphistylic suspension.
Hyostylic – jaws suspended from hyomandibula alone: most osteichthyes.
Metautostylic – mandibles attach to cranium via quadrate: Amphibians, modern reptiles, birds.
Craniostylic – maxilla incorporated into cranium, jaws (reduced to dentary alone) suspended
    directly from squamosal bone.

Postcranial axial skeleton.
Vertebral column: Development.                                    Understand resegmentation.

Evolution of vertebral column.

Primitive fish groups have only notochord w/ a few cartilaginous arch support elements.
Sarcopterygia – arches develop neural spines and hemal spines. Rudimentary centrum elements develop.

 More advanced fishes (including chondrichthyans and osteichthyans) develop amphicoelous centra. 
Arch bases present.
Neural arches well developed, but lack zygapophyses.
Sharks develop intercalary cartilages between neural arches.

Tetrapods – zygapophyses evolve.

Centra include ventral crescentic intercentra and paired pleurocentra.
Vertebral pattern modifications:
Temnospondyls – intercentrum dominant, pleurocentra reduced
Anthracosaurs – pleurocentrum dominant, intercentrum reduced – gives rise to amniote
Embolomeres – pleurocentrum and intercentrum codominant in a 2-centrum vertebra.
Ancestry of lissamphibian centrum unknown.

Know and recognize the following vertebral patterns:
Amphicoelous         Procoelous         Opisthocoelous        Acoelous (=platycoelous)            Heterocoelous
Accessory articular structures evolve in some vertebrate groups:  Zygosphene – zygantrum articulation
Specialized vertebral types within column:
Atlas               Axis            Sacrum (know synsacrum of birds)              Caudal region

Ribs – know anatomy.
In fishes: two types: dorsal and ventral ribs.   Tetrapod rib  homologous to dorsal.

Know relationship between rib and vertebrae (articulation points)
Uncinate processes – what are they?  (see birds)

Sternum – composed of sternebrae in some vertebrates, fused in others

Appendicular Skeleton.
Paired appendages absent in earliest vertebrates.
Median fins effective in preventing roll and yaw
Appendicular fins effective in preventing roll and pitch

Appendicular fins with narrow, moveable basal joint also useful for steering and braking
as well as for slow locomotion in some groups.

Origins of appendages:
Know two theories:
Gill arch theory of Gegenbaur
Fin fold theory of Balfour and Thacher

Parts of fin skeleton:                         Parts of tetrapod limb skeleton:
Basal pterygiophores                       stylopodium
Radial pterygiophores                      zeugopodium
Ceratotrichia                                      autopodium

Pectoral girdle

Dermal elements: Cleithrum, clavicle and interclavicle
Endochondral elements: scapulocoracoid – scapula, procoracoid and coracoid
Know which taxa have these parts.
Know phylogenetic progression of anatomy.
What is the furculum?

Pelvic girdle: puboischiadic bar, Ilium, ischium, pubis.
Know which taxa have these parts.
Know phylogenetic progression of anatomy.
What is the acetabulum?
What is the prepubis?
What is the saurischian condition? What is the ornithischian condition?
Autopodium – Carpals and tarsals, Metapodials and phalanges.
Know phylogenetic progression of anatomy, including primitive condition and changes in
carpal and tarsal bones.

Know digital formulae,

Know the following terms:
Hallux                                      sesamoid
Pollex                                      tibiotarsus
Polydactyly                             carpometacarpus
Hyperphalange                      tarsometatarsus
Understand adaptive changes in foot morphology that have occurred, for example, in frogs, which
have a saltatorial style of locomotion.

Know plantigrade, digitigrade and unguligrade foot postures in mammals. 
Which types of mammals have which types of posture?

The Muscular System.

Muscular tissues are the primary effectors in the vertebrate body.
All forms of movement in vertebrates are produced by muscles

Three types of muscle tissue: striated, cardiac, and smooth.
This section is primarily concerned with striated muscle tissue.

Muscle cells are generally referred to as fibers.
Know terminology of fiber parts: sarcolemma, sarcoplasm, myofibrils, myofilaments, myosin and actin.

Know the muscle subunits and their connective tissue coverings: epimysium, fascicles and perimysium,
fibers and endomysium.
Connective tissue attachments are tendons and aponeuroses.

Muscle morphology: strap-like, spindle-shaped and pennate.  Three types of pennate muscle
include: unipennate, bipennate and multipennate.  Muscles may also be segmented.

Know the relationships among the following:
Paraxial mesoderm                             Myotome
Somites                                                 Myomeres

Major muscle groups:
Extrinsic ocular muscles: 4 rectus, 2 obliques, retractor bulbi and levator palpebrae (the latter
2 are only in tetrapods).
Epibranchial muscles
Hypobranchial musc.
Branchiomeric musc.
Epaxial musc.
Hypaxial musc.
Appendicular musc. (derived from hypax.)

Evolutionary Patterns of the major muscle groups, including the ocular muscles, epaxial,
hypaxial, branchiomeric, appendicular and branchial musculature in various groups, especially the
jaw musculature.

Electrical Organs: be able to explain and diagram an electroplaque.  Give examples of fish that have
these.  What are their uses?

Dentition: Know the following:

The anatomical structure of a typical mammalian tooth.
Tooth development

Mammalian dental formulae.  Know the primitive metatherian and eutherian formulae and some
other examples, such as cat and human.

Homodonty                              Hypsodonty               Diastema
Heterodonty                             Bunodonty                 Thecodont
Polyphyodonty                         Selenodonty               Acrodont
Diphyodonty                            Lophodonty                 Pleurodont
Deciduous dentition                Carnassial dentition

See also: handout on dentition.

Exam date changes: Lecture Exam II will be held on Wednesday, October 29.  It will cover everything from
                                            the lecture on joints to the lecture on dentition, inclusive.
                                     Lab Practical II will be postponed until Thursday, November 6, and will cover the entire
                                            muscular system.

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