Mammal Cranial Skeleton

Question 1

Define cranium

Answer 1

The bones of the entire skull except the mandible.

Question 2

Define neurocranium

Answer 2

The encasement of the brain.

Question 3

Define calvaria

Answer 3

The skull cap, top of the neurocranium.

Question 4

Define basicranium

Answer 4

The bottom of the neurocranium.

Question 5

Define splanchnocranium

Answer 5

AKA the viscerocranium, the facial skeleton.

Question 6

How many bones are there in the human skull, cranial and facial and what are they called?

Answer 6

22 bones
8 cranial (surround cranial cavity and in contact with meninges) : sphenoid, ethmoid frontal, occipital , parietal (x2), temporal (x2)

14 facial (supports the teeth, form the nasal cavities and orbit, not in contact with meninges) : mandible, zygomatic bone (x2), maxilla (x2), inferior nasal conchae (x2), palatine bone (x2), lacrimal bone (x2), nasal bone (x2), vomer

Question 7

Define meninges

Answer 7

Membranes around the brain

Question 8

Detail the sphenoid bone

Answer 8

Body is the most medial aspect with two air sinuses on either side.
Has lesser wings placed superiorly to greater wings (which stretch to the lateral parts of the cranium).
Inferiorly there are 4 pterygoid processes, 2 medial and 2 lateral.

Question 9

Detail the ethmoid bone

Answer 9

Acts as roof of nasal cavity and superior part of the nasal septum.
Superior and middle turbinates/concha like on the lateral walls. These walls also act as the medial wall for the orbits.
Ethmoid air cells lie between lateral wall of nasal cavity and medial wall of orbit.
Superiorly lies cribriform plate and then crista galli.

Question 10

Detail the frontal bone

Answer 10

Forms the forehead and part of the rood of the cranium.
Forms the roof of the orbits.
Contains the frontal sinus.

Question 11

Detail the occipital bone

Answer 11

At rear of cranium and forms the majority of the base of the skull.
Forms the foreamen magnum which encircles the spinal cord.
Has 2 occipital condyles which articulate with the atlas (C1 vertebrae).
External occipital protuberance at centre which gives attachment to nuchal ligaments which stretches down the spinous processes.
Nuchal lines mark neck muscle attachments.

Question 12

Detail the parietal bones

Answer 12

Known as wall of skull, it is bordered by 4 sutures - coronal, sagittal, lambdoid, squamous.
The two bones are connected via the sagittal suture.
Temporal line is marked on this bone due to the temporalis muscle attachment.

Question 13

Detail the temporal bones

Answer 13

Form the lateral walls and part of the floor of the cranial cavity.
Contains the inner and middle ear (ossicles: malleus, incus, stapes).

Question 14

Detail the mandible

Answer 14

Only moving bone in the skull.
Holds lower teeth in places.
Condyloid process attaches to mandibular fossa at the temporomandibular joint on the temporal bone .
Mandibular foreamen for inferior access for alveolar nerve.
Mental foreamen for anterior access for mental nerve which innervates mandible.

Question 15

Detail the zygomatic bones

Answer 15

Cheekbones as well as providing lateral wall for orbits.

Temporal process joins to zygomatic process on temporal bone creating the zygomatic arch.

Question 16

Detail the maxillae

Answer 16

Form the floor of the orbits.
Inferior to this lies the infraorbital foreamen which allow access to infraorbital nerves.
Forms the upper jaw.
Forms anterior 2/3 of hard palate.
Incisive foreamen behind incisors for nerve access.

Question 17

Detail the inferior nasal conchae

Answer 17

Can be called inferior turbinates.
Turbinate a it is shaped like a scroll to provide the function of specific air movement.
Humans have 3 turbinates, mammals with snouts have a more complex structure to aid with sense of smell.

Question 18

Detail the palatine bones

Answer 18

Back to back L-shaped bones which are part of the lateral nasal wall.
Form a small part of the orbital floors.
Form poster 1/3/ of hard palate that maxilla does not.

Question 19

Detail the lacrimal bones

Answer 19

Forms the medial wall of the orbit.
Lacrimal fossae formed between lacrimal and maxillae housing the lacrimal sac (where tears collect and drain into the nasal cavity).

Question 20

Detail the nasal bones

Answer 20

Form the bridge of the nose and support the nasal cartilage.

Question 21

Detail the vomer bone

Answer 21

Supports the nasal cartilage.

Forms inferior half of the nasal septum.

Question 22

Detail the temporalis muscle

Answer 22

Muscle of mastication which is fan shaped and functions to elevate the mandible to close the jaw.
Lies inferiorly to the inferior temporal line.
Inserted at the coronoid process and the anterior surface of the ramus of the mandible.
Muscle fibres pass behind zygomatic arch.
Innervated by mandibular and cutaneous nerves.
Blood supplied superficially by superficial temporal vessels and deeply by maxillary artery.

Question 23

Detail the masseter muscle

Answer 23

Muscle of mastication which is large and rectangularly shaped and functions to elevate the mandible and occlude the teeth (bite).
Stretches from zygomatic process of maxilla and lower border of zygomatic arch to the ramus of the mandible.
Anterior fibres slope backwards and are more superficial whilst posterior fibres are deeper and reach to coronoid process.
Innervation by mandibular nerve through mandibular notch and superficially via facial nerve.
Blood supplied superficially by facial artery.
Parotid duct also present.

Question 24

Define cladistic apomorphy and give an example from the human skull

Answer 24

Branching away from an original shape. e.g. modern humans developing the chin so being a distinguisher from previous human ancestors.

Question 25

Explain the relationship between brain size and cranial structure

Answer 25

• As brain size increases, the face has to rotate downwards and the nose directs are up into the olfactory area.

Question 26

Explain the relationship between bipedalism and cranial structure

Answer 26

• As the human began to stand up, the spine had to rotate downwards and so the foreamen magnum would move more inferiorly and posteriorly to allow this.

Question 27

Describe the distinguishing cranial features of carnivora

Answer 27

Large sagittal crest for large mastication muscle attachment. Orbits facing forward for binocular vision and depth perception. Tight temporomandibular joint and hooked angular process on mandible for a powerful bite - not suitable for grinding. Pronounced nuchal crest for strong neck muscle attachment. Mixed dentition: large canine teeth, crushing molars and distinct carnassial (shearing) teeth behind canines.

Question 28

Describe the distinguishing cranial features of artiodactyla

Answer 28

(Even-toed ungulates or cloven-hooved mammals). No sagittal crest. Orbits face laterally for peripheral vision. Loose temporomandibular joint so allows sideways grinding aided by large masseter muscles - no angular process on mandible. Narrow nuchal crest to hold p head but weak with sideways movements. Continuously growing molars adapting to wear from vegetarian diet. Grooves in teeth to aid tear of vegetation. No upper incisors, lower incisors meet a bony palate instead. Diastema (large gap) between incisors and molars. Lack canines or modified to tusks. Bony structures support antlers which are sometimes present and are temporary (often seasonal for breeding).

Question 29

Why is the pig an exception to the artiodactyl group?

Answer 29

They are omnivores so use canine teeth. They have more frontally aligned orbitals, a tall narrow nuchal crest They also have long paroccipital process which attaches digastric muscles for jaw movement.

Question 30

Describe the distinguishing cranial features of two types of placental mammals: rodentia and lagomorpha.

Answer 30

Rodentia (to gnaw): No sagittal crest Laterally facing orbits Loose temporomandibular joint 4 incisors, 2 upper and 2 lower which continually grow and sharpen on each other - formed from enamel surface and soft dentine inside. No canine, diastema between incisors and molars. Large molars which grow continuously and have altering enamel and dentin layers. Lagomorpha (rodentia with fenestrae present): Similar to rodentia. 4 upper incisors, front two resembling that of rodents but with extra pair lying behind these.