Cranial Cavity Anatomy PDF

The Cranial Cavity Lec: 7 The cranial cavity contains the brain and its surrounding meninges, portions of the cranial nerves, arteries, veins, and venous sinuses. Vault of the Skull The internal surface of the vault shows the coronal, sagittal, and lambdoid sutures. In the midline is a shallow sag...

The Cranial Cavity Lec: 7 The cranial cavity contains the brain and its surrounding meninges, portions of the cranial nerves, arteries, veins, and venous sinuses. Vault of the Skull The internal surface of the vault shows the coronal, sagittal, and lambdoid sutures. In the midline is a shallow sagittal groove that lodges the superior sagittal sinus. On each side of the groove are several small pits, called granular pits, which lodge the lateral lacunae and arachnoid granulations. Several narrow grooves are present for the anterior and posterior divisions of the middle meningeal vessels as they pass up the side of the skull to the vault. Base of the Skull The interior of the base of the skull is divided into three cranial fossae: anterior, middle, and posterior. The anterior cranial fossa is separated from the middle cranial fossa by the lesser wing of the sphenoid, and the middle cranial fossa is separated from the posterior cranial fossa by the petrous part of the temporal bone. Anterior Cranial Fossa The anterior cranial fossa lodges the frontal lobes of the cerebral hemispheres. It is bounded anteriorly by the inner surface of the frontal bone, and in the midline is a crest for the attachment of the falx cerebri. Its posterior boundary is the sharp lesser wing of the sphenoid, which articulates laterally with the frontal bone and meets the anteroinferior angle of the parietal bone.The medial end of the lesser wing of the sphenoid forms the anterior clinoid process on each side, The crista galli is a sharp upward projection of the ethmoid bone in the midline for the attachment of the falx cerebri. Alongside the crista galli is a narrow slit in the cribriform plate for the passage of the anterior ethmoidal nerve into the nasal cavity. The upper surface of the cribriform plate supports the olfactory bulbs, and the small perforations in the cribriform plate are for the olfactory nerves. Middle Cranial Fossa The middle cranial fossa consists of a small median part and expanded lateral parts. The median raised part is formed by the body of the sphenoid, and the expanded lateral parts form concavities on either side, which lodge the temporal lobes of the cerebral hemispheres. It is bounded anteriorly by the lesser wings of the sphenoid and posteriorly by the superior borders of the petrous parts of the temporal bones. Laterally lie the squamous parts of the temporal bones, the greater wings of the sphenoid, and the parietal bones. The floor of each lateral part of the middle cranial fossa is formed by the greater wing of the sphenoid and the squamous and petrous parts of the temporal bone. The sphenoid bone resembles a bat having a centrally placed body with greater and lesser wings that are outstretched on each side. The body of the sphenoid contains the sphenoid air sinuses, which are lined with mucous membrane and communicate with the nasal cavity; they serve as voice resonators. Anteriorly, the optic canal transmits the optic nerve and the ophthalmic artery (branch of the internal carotid artery, to the orbit). The superior orbital fissure, which is a slit-like opening between the lesser and the greater wings of the sphenoid, transmits the oculomotor(III), trochlear(IV), lacrimal, frontal, and nasociliary branches of ophthalmic division(V1) of the trigeminal n., and abducent(VI) nerves, together with the superior ophthalmic vein. The foramen rotundum, which is situated behind the medial end of the superior orbital fissure, perforates the greater wing of the sphenoid and transmits the maxillary nerve. The foramen ovale lies posterolateral to the foramen rotundum. It perforates the greater wing of the sphenoid and transmits the mandibular nerve. Middle Cranial Fossa The small foramen spinosum lies posterolateral to the foramen ovale and also perforates the greater wing of the sphenoid. The foramen transmits the middle meningeal artery. The large and irregularly shaped foramen lacerum lies between the apex of the petrous part of the temporal bone, the sphenoid bone and the occipital bone. The inferior opening of the foramen lacerum in life is filled by cartilage and fibrous tissue, and only small blood vessels pass through this tissue from the cranial cavity to the neck. Middle Cranial Fossa On the anterior surface of the petrous bone are two grooves for nerves; the largest medial groove is for the greater petrosal nerve, a branch of the facial nerve; the smaller lateral groove is for the lesser petrosal nerve, a branch of the tympanic plexus. The greater petrosal nerve enters the foramen lacerum The lesser petrosal nerve passes forward to the foramen ovale. The superior angles of the dorsum sellae have two tubercles, called the posterior clinoid processes, The cavernous sinus is directly related to the side of the body of the sphenoid. It carries in its lateral wall the 3rd and 4th cranial nerves and the ophthalmic and maxillary divisions of the 5th cranial nerve. The internal carotid artery and the 6th cranial nerve pass forward through the sinus. Posterior Cranial Fossa The posterior cranial fossa is deep and lodges the parts of the brain, namely, the cerebellum, pons, and medulla oblongata. Anteriorly, the fossa is bounded by the superior border of the petrous part of the temporal bone, and posteriorly it is bounded by the internal surface of the squamous part of the occipital bone. The floor of the posterior fossa is formed by the occipital bone and the temporal bone. The internal occipital crest runs upward in the midline posteriorly from the foramen magnum to the internal occipital protuberance; On each side of the internal occipital protuberance is a wide groove for the transverse sinus. This groove sweeps around on either side, on the internal surface of the occipital bone, to reach the parietal bone. The groove now passes onto temporal bone, and here the transverse sinus becomes the sigmoid sinus. The superior petrosal sinus drains into the sigmoid sinus.  Neonatal Skull The newborn skull, compared with the adult skull, has a disproportionately large cranium relative to the face. In childhood, the growth of the mandible, the maxillary sinuses, and the alveolar processes of the maxillae results in a great increase in length of the face. The bones of the skull are smooth and unilaminar, there being no diploë present. Most of the skull bones are ossified at birth, but the process is incomplete, and the bones are mobile on each other, being connected by fibrous tissue or cartilage. The bones of the vault are ossified in membrane; the bones of the base are ossified in cartilage. The bones of the vault are not closely knit at sutures, as in the adult, but are separated by unossified membranous intervals called fontanelles. Clinically, the anterior and posterior fontanelles are most important and are easily examined in the midline of the vault. The anterior fontanelle is diamond shaped and lies between the two halves of the frontal bone in front and the two parietal bones behind. The fibrous membrane forming the floor of the anterior fontanelle is replaced by bone and is closed by 18 months of age. The posterior fontanelle is triangular and lies between the two parietal bones in front and the occipital bone behind. By the end of the 1st year, the fontanelle is usually closed. The mandible has right and left halves at birth, united in the midline with fibrous tissue. The two halves fuse at the symphysis menti by the end of the 1st year. The angle of the mandible at birth is obtuse, the head being placed level with the upper margin of the body and the coronoid process lying at a superior level to the head. It is only after eruption of the permanent teeth that the angle of the mandible assumes the adult shape and the head and neck grow so that the head comes to lie higher than the coronoid process.