Cranium

The cranium consists of 23 bones of the cranium of 15 different types, with the exception of the mandible and hyoid bones, that are immovably connected. The cranium can be divided embryologically into neurocranium and viscerocranium. With the exception of the skull base, the majority of the bones of cranium undergoes membranous ossification, which differs from the ossification of the bones of the extremities (cartilaginous ossification).

The head has long been of interest to anatomists. Goethe, the great writer, was the first to describe that the intermaxillary bones (incisive bone, premaxilla) that animals have are also present in humans. He also put forth the idea (partially correct) that the cranium is a deformed version of the vertebrae. This was the beginning of "morphology". Physical anthropologists devised various measurements and scientifically classified races (!?) according to cranial index (maximum cranial width/maximum cranial length), facial angles (indicating protrusion of the maxilla), and so on.

Fossils of australopithecine (ape-man) from 2 to 3 million years ago indicate that their neurocranium capacity was not different from that of modern apes. Nevertheless, he (she) is classified as a human being. This is because various evidences, such as the inclination of the occipital condyles and the morphology of the leg bones, suggest that he (she) walked upright and bipedal. In other words, humans became humans by standing up before their brains developed.

The eye-ear-plane, (Frankfurt horizontal plane), is generally used as the reference plane when measuring the cranium. This plane is defined by the uppermost point of the left and right external acou stic opening and the lowermost point of the left orbital cavity. When measuring body height, for example, this plane is parallel to the floor (as it is when the chin is pulled back).

Let us compare the human cranium with those of other mammals and primates. Then, let us consider anatomically what makes us human.
1. Cranium as a brain container
Let us define it as the skeletal case that contains the brain. This does not necessarily correspond to what comparative anatomists call the brain case, the neurocranium, nor does it correspond to the part composed of the bones of cranium. Let us consider the part above the eye-ear-plane. And let us observe the lid (ceiling, calvaria) and the bottom (floor, cranial base) of the brain container.
1-1. External surface of calvaria
The calvaria belong to the dermal bones (exoskeleton). This bone is a bony structure that arises primarily within the dermis and not as pre-existing cartilage (i.e., membranous bone). In vertebrates, this dermal bones are found in crustaceans fossils from about 450 million years ago (think lamprey in armor, right?). In humans, the remnants are found in the calvaria and part of the clavicle. The limb skeletons, incidentally, are classified as endoskeletons.
・Sagittal suture (1-1)・Coronal suture (1-2)・ Lambdoid suture (1-3)
・Frontal / metopic suture (2)
In the majority of adults, it does not exist because of fusion disappearance.
Do not mistake the radiographic image for a fracture line.
・Sutural bone(Interparietal bone ,Inca bone)(3)
・Frontal tuber (4-1)・Parietal tuber (4-2);What's left of it.
・Bregma ---- Anterior fontanelle (5)
・Lmbda ---- Posterior fontanelle (6)
・External occipital protuberance (7) ;Touch it with a living body.
・Highest nuchal line (8-1)・Superior nuchal line (8-2) ・Inferior nuchal line (8-3)
What will attach to each
・Squamous suture (9) ;How is it different from other sutures
・Superior temporal line (10-1)・Inferior temporal line (10-2);What will attach to
・External acoustic opening (11)---- External acoustic meatus;The form is
・Mastoid process (13)(54);What will attach to
Touch it in your body
・Mandibular fossa (14)(62);What fits in
1-2. Internal surface of the calvaria
・Compare the fusion and disappearance of suture between the external and internal surfaces.
・Groove for superior sagittal sinus (16);What and where to run
・Granular foveolae(17);What's in it
・Parietal foramen (18); What and where to go
・Arterial grooves (19) ;What runs
Which foramen to start with
1-3. Internal surface of cranial base
・Anterior cranial fossa (20-1)・Middle cranial fossa (20-2)・Posterior cranial fossa (20-3)
To which part of the brain do the height and size of each fossa correspond
1-3-1. Anterior cranial fossa
・Frontal bone (21-1) ,Ethmoidal bone (21-2),Sphenoidal bone (21-3) ;Identify the bones
・Cribriform plate (22) ;What is and where is it going
・Crista galli (23);What attach to it
・Impressions of cerebral gyri (23-1);What does this correspond to
1-3-2. Middle cranial fossa
・Identify the sphenoidal and temporal bonea
・Sella turcica (24),Dorsum sellae (25)
Hypophysial fossa (26); What is the size of it
・Optic canal(27)(77);What is and where is it going
・Superior orbital fissure;What is and where is it going
・Foramen rotundum (29); What passes
Carotid canal (30)(58);What and how to pass
・Foramen lacerum (31)(61) <---- Groove for greater petrosal nerve (32)
What will run in it
・Groove for lesser petrosal nerve
What will pass
・Foramen ovale of sphenoidal bone (34)(66)
What will pass through
・Foramen spinosum (35)(65) ;What passes and where it leads
・Petrous part(pyramis)(36) ;What's inside
Arcuate eminence (37); What it corresponds to(Important!)
・Trigeminal impression (38);What's on board
・Internal acoustic opening (39) ----> Internal acoustic meatus
What passes and where to
・Opening of vestibular canaliculus
What is the opening for
1-3-3. Posterior cranial fossa
・Identify the Occipital bone (42) ,Sphenoidal bone (43),Temporal bone (44)
・Clivus (45);What's on board
・Foramen magnum (46)
Size, shape, what passes through
・Hypoglossal canal;What will pass through
・Groove for transverse sinus (48) ----> Groove for sigmoid sinus (49)
Where it comes from
・Jugular foramen (50)(59)
What will pass through
Which bones are composed of
1-4. External surface of cranial base
・Identify the occipital bone , temporal bone , sphenoidal bone.
・Occipital condyle (52)---- Atlanto-occipital joint
The shape and the direction of the major axis are
Movement at the joint
・Condylar canal (53)
What will pass through
・Mastoid process (54)(13);What attach to
Touch it in your body
Occipital groove (55);What will pass
・Styloid process (56) ;Originating from which gill arch What attach to
・Stylomastoid foramen (57)
What and where it comes from
・Carotid canal (58)(30);Where it leads
・Jagular foramen (59)(50);Imperfectly bifurcated, its meaning is
・Tympanic canaliculus (60);What and where to pass through
・Foramen lacerum (61) (31);What is happening in the living body
・Mandibular fossa (62)(14)---- Temporomandibular joint
Movement
・Petrotympanic fissure (64);What and where to pass through
・Foramen spinosum (65) (35);What passes
・Foramen ovale of sphenoidal bone (66)(34) ;What passes
・Sulcus of auditory tube (67);From where and to where
・Musculotubal canal
What passes through
2. Bones of face
Let's think of it as the area below the eye-ear horizontal plane. This does not necessarily correspond to the viscerocranium or the part composed of the facial bones. Can we think of it as a skeleton containing the visual, olfactory, respiratory, and digestive organs? Some of the bones belonging to this section and the auditory ossicles are derived from the gill arch. Look them up in an embryology book.
2-1. Orbit
The bones that make up the orbit are paper thin, so handle them with care!
Orbital cavity
Fontal bone (68)
Zygomatic bone (69)
Sphenoidal bone (70)
Mxilla (71)
Ethmoidal bone (72)
Lacrimal bone (73)
Palatine bone (74)
Identify these bones mentioned above.
・Supra-orbital foramen (notch) (75);What will pass through
Try to touch it in your body
・Frontal foramen (notch) (76);What will pass through
It may have become common with the former foramen and become a single foramen (notch).
2-1-1. Roof of orbit
・Optic canal (77)(27);What passes and where it leads
・Fossa for lacrimal gland (78);What fits in
2-1-2. Lateral wall of orbit
・Superior orbital fissure (79)
What passes and where it intersects
・Inferior orbital fissure (80)
What passes and where it intersects
2-1-3. Floor of orbit
・Infra-orbital groove (81);What will pass through
↓ Infra-orbital canal
↓ Infra-orbital foramen (83)
2-1-4. Medial wall of orbit
・Anterior and posterior ethmoidal foramen
What passes and where it intersects (Very complicated!)
・Fossa for lacrimal sac (85)(Don't mistake it for the fossa for lacrimal gland!)
・Nasolacrimal canal (86)
Remnants of posterior nostrils in fishes.
What passes and where does it lead
Consider the anatomical reasons why horseradish stings the eyes.
2-2. Zygomaic arch
・Touch it with your body. Compare the protrusion of it with your neighbor's.
・Which bones are made up of
・Zygomatico-orbital foramen
zygom_foramen.JPEG
2-3. Bony nasal cavity
・Piriform aperture (87)
・Nasal bone (88);The slope determines the nose depth (distance from the pronasale to the subnasale points) or so-called nose height. The anthropometric method determines nase height as the distance from the sellion/nasion to the subnasale points. This nose height is the so-called nose length.
Nasion (89) ;Difficult to detect in living body.
・Choana (90)
2-3-1.Floor
・Palatine bone (91)
・Bony nasal septum (92);How is the curvature
= os ethmodale(93-1)+ Vomer(93-2)
2-3-2. Sidewall
・Superior nasal chonca (94-1),Middle nasal chonca (94-2),Inferior nasal chonca (94-3)(The inferior nasal chonca is an independent bone!)
Superior nasal meatus (95-1),middle nasal meatus(95-2),inferior nasal meatus(95-3)
・Nasopharyngeal meatus (97) ----> Choana

The next part can be clearly observed by looking through the piriform aperture of the halved specimen from anteriorly downward.
・Ethmoidal bulla (98)
・Uncinate process of ethmoidal bone (99)
・Semilunar hiatus (100);Which paranasal sinuses open
・Sphenopalatine foramen (101);Where to communicate with where
2-4. Bony palate
・= Maxilla + Palatine bone
・Transverse palatine suture (102)
・Median palatine suture (103)
・Incisive suture(Disappearing in adults.)
[Incisive bone(Intermaxillary bone, premaxilla)](It is found in the fetal period. Goethe described that it is also present in humans.)
・Incisive fossa (105)
Incisive canal (106) ;What passes for
・Teeth
The percentages of erupted, erupted, and tooth-bud missing third molars are about 1/3 each.
・Greater palatine foramen (108) ---- Greater palatine canal
What passes and where it communicates with
・Lesser palatine foramen (110)---- Lesser palatine canal
What passes and where it communicates with
2-5. Pterygopalatine fossa and surroundings
・Pterygoid process;What will attach
Lateral plate of pterygoid process (112),Medial plate of pterygoid process (113)
Pterygoid hamulus (114);Tensor veli palatini muscle goes around
・Pterygoid fossa (115)
Pterygopalatine fossa (116);The following structures are gathered. Check them through fishing lines.

   Foramen rotundum;To backward and upward
   Inferior orbital fissure;To forward and upward
   Greater palatine canal;To downward
   Sphenopalatine foramen;To inward
   Pterygoid canal (121);To backward
2-6. Mandible
・Body of mandible (122)
・Ramus of mandible (123)
・Teeth
・Mental protuberance (125);Human traits!
Mental tubercle(Boundaries are indistinct.)
・Mental foramen (127); What will path through
Supra-orbital foramen, Location with infra-orbital foramen
・Angle of mandible (128); Touch yourself.
・Condylar process of mandible (129) ---- temporomandibular joint
・Coronoid process of mandible (130); What attaches to
・Pterygoid fovea (131); What will attach to
・Pterygoid tuberocity (132);What attaches to
・Mandibular foramen (133) ---- Mandibular canal
What passes and where it runs to
・Mylohyoid line (135); What will attach to
・Mylohyoid groove (136); What passes through
・Superior and inferior mental spine (137); What attaches to
・Digastric fossa (138); What will atach to
2-7. Hyoid bone
・Touch it in living body, but do not mistake it for thyroid cartilage.
・From which gill arch is it derived?
・Body (139)
・Greater horn of hyoid bone (140)
・Lesser horn

(References)  I hope you now understand the significance of the many foramens, fissures, and grooves in the cranium. The anatomy of these structures is a very difficult part of the dissection practice.
 Here is a summary of the parasympathetic pathways going from some cranial nerves to the glands. Let's follow them with a thinn wire or fishing line. The terms in [ ] are osteological structures.

  1. From glossopharyngeal nerve to parotid gland
    Glossopharygeal nerve --> Tympanic nerve --> [tympanic canaliculus]--> tympanic plexus --> [tympanic cavity] --> lesser petrosal nerve --> [groove for lesser petrosal nerve] --> [shpenopetrosal fissure] --> [foramen ovale ] --> otic ganglion --> parotid gland
  2. From facial nerve to submandibular gland and sublingual gland
    facial nerve --> chorda tympani --> [canaliculus for chorda tympani] --> [tympanic cavity] --> [petrotympanic fissure] --> lingual nerve --> submandibular ganglion --> submandibular gland and sublingual gland
  3. From facial nerve to lacrimal gland
    facial nerve --> greater petrosal nerve --> [groove for greater petrosal nerve] --> [foramen lacerum] --> [pterygoid canal] --> nerve of pterygoid canal --> pterygopalatine ganglion --> [inferior orbital fissure] --> lacrimal nerve --> lacrimal gland

 The connections between the nerves, plexus, and ganglia described here are of gross anatomical view, not necessarily neural junctions. Pay close attention!


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