A2 - Os sphenoidale

Question 1

What is the cranium formed by?

Answer 1

• Roof:
  
  • Os interparietale
  • Os parietale
  • Os frontale
• Lateral walls on each side:
  
  • Os temporale
• Floor:
  
  • _​_Os sphenoidale
    
    • Os praesphenoidale
    • Os basisphenoidale
  • Os occipitale, pars basilaris
• Nuchal wall:
  
  • _​_Os occipitale, pars squamosa
  • Os occipitale, pars lateralis
• Nasal wall:
  
  • _​_Os ethmoidale

Question 2

What does os sphenoidale form?

Answer 2

The rostral part of the base of the skull

Question 3

What are os sphenoidale divided into?

Answer 3

• Os presphenoidale
• Os basisphenoidale
• Both parts comprise:
  
  • Median body (corpus)
  • Wings (alae osisis praesphenoidale, ala ossis basisphenoidale)
  • Processus pterygoideus

At birth the two parts are united by synchondroses intersphenoidalis, which becomes ossified during the first years of life

Question 4

Structures to mention on os praesphenoidale

Answer 4

Corpus

• Jugum sphenoidale
• Rostrum sphenoidale
• Crista sphenoidalis
• Sulcus chiasmatis (in caudal part of os presphenoidale. Houses chiasma opticum. Marked by the crista orbitosphenoidalis)
• Crista orbitosphenoidalis (Marks sulcus chiasmatis)
• Sinus sphenoidalis (paired)
  
  • ​Septum sinuum sphenoidalium
• Fossa cranii rostralis (forms the wings)

Ala [=orbitalis]

• Canalis opticus (at the root of the wings. Leads to the orbit. Houses n. opticus)
• Fissura orbitalis (ca, eq) (lies below and behind canalis opticus)
• Foramen rotundum (lies below fissura orbitalis. Ca, eq: opens rostrally into canalis alaris)
• Foramen orbirotundum (bo) (for. rotundum and fissura orbitalis unite)
• Foramen opticum
• Incisura ethmoidalis (eq)
• Processus clinoideus rostralis

Question 5

Give the interspecies differences on os praesphenoidale

Answer 5

• Ala
  
  • Fissura orbitalis (ca, eq)
  • Incisura ethmoidalis (eq)

Question 6

What does ala ossis presphenoidalis form?

Answer 6

• The outer surface participate to the formation of the orbit
• The inner surface forms the cranial cavity

Question 7

Structures to mention on os basisphenoidale

Answer 7

Corpus

• Fossa cranii media (formed by the body and wings of the basisphenoid)
• Sella turcica (on the floor ot the cranial cavity)
  
  • Fossa hypophysialis
  • Dorsum sellae (Ø eq)
    
    • Processus clinoideus caudalis
• Sulcus caroticus (eq, ca)

Ala [=ala temporalis]

• Foramen rotundum (eq, ca)
• Foramen caroticum (ca) (formed by pars tympanica od os temporale)
• Foramen ovale (ca, bo)
• Foramen spinosum (ca)
• Fossa piriformis (houses lobus piriformis of the brain. Lateral from sulcus n. maxillaris)
• Spina ossis sphenoidalis
• Sulcus n. ophthalmici (ca, eq) (medial one, communicates with fissura orbitalis)
• Sulcus n. maxillaris (ca, eq) (lateral one, leads to for. rotundum)
• Sulcus nn. ophthalmici et maxillaris (bo, su) (on the cerebral surface, connects the for. orbirotundum with the orbit)
• Foramen lacerum (eq, su) (the caudal border of each wing demarcates the rostral margin)
  
  • Incisura carotica (eq, su) (medial. Eq: doubled)
  • Incisura ovalis (eq, su) (lateral)
  • Incisura spinosa (eq, su)

Processus pterygoideus

• Canalis alaris (eq, ca)
  
  • Foramen alare rostrale
  • Foramen alare caudale
  • Foramen alare parvum (eq)
• Crista pterygoidea (Ø ca)
• Canalis pterygoideus
• Sulcus n. canalis pterygoidei

Question 8

Give the interspecies differences on os basisphenoidale

Answer 8

Corpus

• Sella turica
  
  • Dorsum sellae (ø eq)
• Sulcus caroticus (eq, ca)

Ala [=ala temporalis]

• Foramen rotundum (eq, ca)
• Incisura carotica (eq: dupla, su)
• Foramen caroticum (ca)
• Foramen ovale (ca, bo)
• Incisura ovalis (eq, su)
• Foramen spinosum (ca)
• Incisura spinosa (eq, su)
• Sulcus n. opthalmichi (ca, eq)
• Sulcus n. maxillaris (ca, eq)
• Sulcus nn. opthalmichi et maxillaris (bo, su)
• Foramen lacerum (eq)

Processus pterygoideus

• Canalis alaris (eq, ca)
  
  • Foramen alare parvum (eq)
• Crista pterygoidea (ø ca)

Question 9

Os praesphenoidale

Processus pterygoideus

Answer 9

• Arises laterally from the rostral end of os basisphenoid
• Projects downwards, forwards
• Unites with the perpendicular plate of the os palatinum
• Make up the margin of choanae

In powerpoint:

• Hamulus pterygoideus
• Canalis alaris (ca, eq) (on its root)
  
  • For. alare rostrale
  • For. alare caudale
  • For. alare parvum (eq)
• Crista pterygoidea (ø ca) (crest continuing proc. pterygoideus dorsally. Borders fossa peterygopalatina)
• Canalis pterygoideus (through the base of proc. pterygoideus)
• Sulcus n. canalis pterygoideus (caudal continuation of canalis pterygoideus)

Question 10

Give the division of the base of the neurocranium

Answer 10

• Fossa cranii rostralis
  
  • ​Between laminae cribosa → alae ossis presphenoidalis
• Fossa cranii media
  
  • ​From the caudal borders of the alae ossis presphenoidalis → crista sphenooccipitalis and crista partis petrosae
• Fossa cranii caudalis
  
  • ​From crisa sphenooccipitalis and cristae partis petrosae → for. magnum

Question 11

Draw the base of the neurocranium

Answer 11

Question 12

Foramens and channels related to os sphenoidale

Answer 12

• For. rotundum (eq, ca)
  
  • For. rotundum → canalis alaris → sulcus n. maxillaris
  • For n. maxillaris
• For. caroticum (ca)
  
  • Rostral to bulla tympani, medial
  • For a. carotis interna
• For. ovale (ca, bo)
  
  • Rostral to bulla tympani, lateral
  • For n. mandibularis (V₃)
• For. spinosum (ca)
  
  • ​Rostral to bulla tympani, next to for. ovale
  • For a. meningea media
• For. lacerum (eq, su) (between os basisphenoidale, os temporale and os occipitale. Unites with for. jugulare through fissura pterooccipitalis?????)
  
  • ​Incisura carotica (su, eq: doubeld)
    
    • Medial
    • For a. carotis interna
  • Incisura ovalis (eq, su)
    
    • Middle
    • For n. mandibularis (V₃)
  • Incisura spinosa (eq, su)
    
    • Lateral
    • For a. meningea media

​Os basisphenoidale, proc. pterygoideus:

• ​Canalis alaris (eq, ca)​ (passage for a. maxillaris
  
  • For. alare rostrale
  • For. alare caudale
  • For. alare parvum (eq)
    
    • For a. temporalis profunda rostralis
• Canalis pterygoideus
  
  • ​For n. canalis pterygoidei
• Sulcus n. canalis pterygoidei​
  
  • ​Caudal continuation of calanis pterygoideus
  • Between corpus and processus pterygoideus of os basisphenoidale