Lecture 4: The Skull Flashcards
What are the 3 components of the axial skeleton?
Skull
Vertebral column
Thoracic cage
What are the 2 components of the appendicular skeleton?
Upper/lower limbs
Pectoral/pelvic girdles
What are the 2 general types of skull bones?
Cranial (neurocranium)
Facial (viscerocranium)
What are the 2 paired cranial bones
Parietal
Temporal
What are the 4 unpaired cranial bones
Frontal
Occipital
Sphenoid
Ethmoid
How many cranial bones do we have?
8
How many facial bones do we have?
14
What are the 6 paired facial bones?
Zygomatic Lacrimal Nasal Palatine Maxillae Inferior nasal conchae
What are the 2 unpaired facial bones?
Vomer
Mandible
What differentiates the mandible of a modern human with that of a lower primate?
In primates, the mandible is 2 parts with a cartilagenous plate separating them at the chin
What suture along the frontal bone is only retained in some?
Metopic suture
The frontal crest lies along the inside of the frontal bone, it acts as the attachment site for the ____________, which is a type of protective connective tissue for the brain
Falx cerebri
What are the attachment points for the temporal musculature on the parietal bone?
Superior and inferior temporal lines
What suture forms the articulation between frontal and both parietal bones?
Coronal
What suture forms the articulation between both parietal bones?
Sagittal
What suture forms the articulation between parietal and occipital bones?
Lamdoid
What suture forms the articulation between the temporal and parietal bones?
Squamous
What is the origin of the sternocleidomastoid muscle?
Mastoid process of the temporal bone
What is the purpose of the groove of the sigmoid sinus (located at the interior of the temporal bone)?
Canal for drainage of blood from the brain
True or false: if you follow through the external acoustic meatus you will exit out the internal acoustic meatus
False, the two are not connected
What is the function of the petrous portion of the temporal bone?
Protection of the inner ear
Petrous = thick/dense
What is unique about the dimorphism of the external occipital protuberance?
It is more prominent in men
When nodding “yes” the occipital condyles articulate with the ________
2 pedicles on the atlas (cervical vertebrae)
What are the 3 grooves in the occipital bone making room for to drain the blood coming out of the brain?
Sigmoid sinus
Transverse sinus
Superior sagittal sinus
The sella turcica is part of what bone, and what is its significance?
Sphenoid - the pituitary gland sits in this cranial depression
What foramen of the sphenoid bone provides an exit point for the maxillary branch of the trigeminal nerve?
Foramen rotundum
What foramen of the sphenoid bone provides an exit point for the mandibular branch of the trigeminal nerve?
Foramen ovale
What foramen of the sphenoid bone provides an exit point for the middle meningeal artery?
Foramen spinosum
The superior orbital fissure is found in which cranial bone?
Sphenoid
What is the significance of the sphenoid bone?
Unites the cranial and facial bones
Articulates with almost every bone in the skull
Contains the sphenoid sinuses
What structure on the ethmoid bone provides an attachment site for the falx cerebri?
Crista galli
What structure on the ethmoid bone forms the medial wall of the orbit?
Orbital plate
What structure on the ethmoid bone forms the superior portion of the nasal septum?
Perpendicular plate
The ethmoidal labyrinth is made up of what 2 structures?
Superior nasal conchae
Middle nasal conchae
The inferior nasal concha is considered its own separate bone
The olfactory nerve descends along the lateral borders of what structure of the ethmoid bone?
Cribriform plate
What aspect of the ethmoid bone forms the passageway for olfactory nerve branches?
Cribriform foramina
What aspect of the vomer bone articulates with the sphenoid?
Ala
What aspect of the vomer bone forms the inferior portion of the nasal septum?
Vertical plate
What aspect of the palatine bone forms part of the medial floor of the orbit?
Orbital process
What aspect of the palatine bone forms the lateral wall of the nasal cavity?
Perpendicular plate
What aspect of the palatine bone forms the posterior portion of the hard palate?
Horizontal plate
What aspect of the maxilla forms the posterior portion of the hard palate?
Palatine process
What aspect of the maxilla separates the hard palate from the anterior nasal spine?
Incisive foramen
What aspect of the maxilla holds the teeth of the upper jaw?
Alveolar process
What is the largest paranasal sinus in the skull?
Maxillary sinus
How many bones make up the orbital complex?
7
What are the 4 paranasal sinuses?
Frontal
Sphenoid
Ethmoid
Maxillary
What are the 4 fontanelles associated with the fetal skull?
Anterior
Sphenoid
Mastoid
Posterior
The cribriform plate allows passage of what cranial nerve(s)?
CN I - Olfactory
The optic canal allows passage of what cranial nerve(s)?
CN II - Optic
The superior orbital fissure allows passage of what cranial nerve(s)?
CN III - Occulomotor
CN IV - Trochlear
CN V (V1) - Ophthalmic division of trigeminal
CN VI - Abducens
The foramen rotundum allows passage of what cranial nerve(s)?
CN V (V2) - Maxillary division of trigeminal
The foramen ovale allows passage of what cranial nerve(s)?
CN V (V3) - Mandibular division of trigeminal
The internal acoustic meatus allows passage of what cranial nerve(s)?
CN VII - Facial
CN VIII - Vestibulocochlear
The jugular foramen allows passage of what cranial nerve(s)?
CN IX - Glossopharyngeal
CN X - Vagus
CN XI - Accessory
The hypoglossal canal allows passage of what cranial nerve(s)?
CN XII - Hypoglossal
In comparing the anapsid reptilian skull with modern mammals/humans, describe changes to the dermatocranium
The anapsid dermatocranium was a very small structure at the back of the skull
In modern mammals/humans, it makes up a larger part of the braincase with parietal and frontal bones
In comparing the anapsid reptilian skull with modern mammals/humans, describe changes to the neurocranium
In the anapsid skull, the neurocranium is what held the brain but it was much smaller than modern humans
In the modern mammal/human skull, the neurocranium includes the occipital and temporal parts of the basocranium
In comparing the anapsid reptilian skull with modern mammals/humans, describe changes to the splanchocranium
In the anapsid skull, the splanchnocranium was the posterior part of the mandible
In the mammal/human skull it becomes the greater wing of the sphenoid
Describe the significance of the appearance and enlargement of fenestrae during vertebrate skull evolution
The anapsid reptilian skull was composed of a small neurocranium with the masticatory muscles almost completely occluded by a helmet of bone; there was no opening beyond the orbit
As the size of the neurocranium increased throughout evolution, there was a development of fenestra (openings) in the skull which led to the complete exposure of masticatory muscles
One of the structures that was retained after fenestra formed about the masticatory musculature is the ____________
Zygomatic arch
What is the significance of the evolution of a secondary plate?
Permits breathing while chewing
Primitive gulp-feeders did not need to breath while eating because they did not utilize oral processing of food as modern mammals/humans do
Describe the transition of mandibular bones to ear ossicles throughout evolution
The mandible becomes less complex, with fewer contributing bones. Ossicles develop from the prior mandibular bones
The convergence and frontation of the orbits that is seen in order primates is not seen in species like rabbits, which have extensive peripheral vision. What is the benefit to humans evolving this way when the downside is a decrease in our peripheral vision?
Convergence and frontation allow for more overlap between peripheral vision and frontal vision, which gives us stereoscopic vision (depth perception) which is further enhanced by color vision
Describe the evolution of the rostrum/snout
There is greater angulation in the skull (flexion), and ultimately shortening of the rostrum/snout
What suture of the skull is straighter in lower primates and has become progressively more curved in humans and our more recent ancestors?
Squamous
What does variation in the development of the supraorbital torus mean in terms of eye placement?
Primates such as chimps and gorillas have a large supraorbital torus, which typically indicates that the eyes protrude more
Starting with homo erectus the torus was lost, as the eyes were set back into the skull more
What structure found in some hominins was theorized to act in one of these two ways:
As a buttress to counteract high masticatory loads
Protection for eye when face is anteriorly displaced from the vault
Supraorbital torus
What is unique about the cranial bone in H. Erectus that is not found in any other hominins?
Markedly thickened cranial bone - unclear why
What accounts for variation in the architecture of the superior aspect of the cranial vault in humans?
This is primarily due to the size of masticatory musculature
What accounts for variation in the architecture of the posterior aspect of the cranial vault in humans?
Decrease in nuchal musculature, need less surface area for muscle attachment since they do not come up as high
What accounts for the variation in position and orientation of the nuchal musculature in Gorilla and modern Homo?
Variation due to facial size and spinal orientation. May also consider position of foramen magnum.
Gorillas primarily walk quadrupedally, so their spinal cord exits more horizontally. They also have a big, heavy face that requires more extensive nuchal musculature to hold it up.
Humans walk bipedally, so the spinal cord exits vertically. Face is shortened and does not need to be lifted up from a horizontal position, so there is less nuchal musculature.
Describe the differences in function of the nuchal ligament in humans vs. other mammals
In quadrupedal mammals, the nuchal ligament helps with neck extension and flexion
In humans, it does not serve these functions due to upright posture
Describe the differences in function of the sternocleidomastoid muscle in humans vs. other mammals
The shift of the head’s center of gravity in bipedal primates demands that the SCM take on the role of flexor AND extensor
Quadrupedal mammals primarily need the SCM as an extensor
The mastoid crest, large occipital torus, long flat skull, and large face are unique morphologies associated with what species of Homo?
H. erectus
What is unique about human facial skeleton development as compared to other primates?
Humans maintain an infantile configuration of the face
Other primates have more facial growth through the course of development from infant to adulthood
Describe the variation in the anterior zygomatic among hominids with anterior pillar Australopithecus
Posterior angulation in the zygomatic is the primitive condition
In hominins, there is anterior angulation at the root of the zygoma that can produce an anterior pillar along the side of the nose. This is a morphology not seen in modern humans or other living primates
What is the function of the anterior pillar seen in lower primates?
Appears to be an adaptation to high masticatory loads passing through the premolar
When doing measurements of facial prognathism, why create facial indices?
Removes the effect of overall size; allows you to compare facial length without considering size of the skull itself in order to compare with others
Describe the relationship between the lacrimal and ethmoid bones in Pan and Homo
Pan - there is barely any contact between lacrimal and ethmoid
Homo - there is distinct contact. This is a synapomorphy among hominins
Is the variation in nasal bone architecture useful for classification of species?
No
What is common to most, if not all, hominins in terms of the mid and upper face?
Flaring of the zygomatic arch
Why is the australopithecine zygomatic flared?
Takes the masseter muscle further from the mandible. With steeply angled masseter, there is opportunity for enhanced lateral movement during mastication
Between A. africanus, P. robustus, P. boisei, and early Homo:
Which has the greatest amount of zygomatic flaring?
Which have anterior pillar?
Which has the most flat/concave face with a broad beam instead of a pillar?
Which have the most robust faces?
Most zygomatic flaring = P. Boisei
Anterior pillar = A. Africanus, P. Robustus
Flat/concave face + broad beam = P. Boisei
Most robust = P. Robustus, P. Boisei
Why does Neanderthal have a pneumatized face?
3 theories:
To cool the body
To warm the incoming air
Simply due to a relatively large face, may not be otherwise functionally significant
