Skull

The skull of the largest fish-eating myotis (Myotis vivesi) is characterized by a short, broad, and tall or dorsally projected rostrum and broad zygomatic arches.

From: The Teeth of Mammalian Vertebrates , 2018

Skull

Sentiel A. Rommel , ... Alexander M. Costidis , in Encyclopedia of Marine Mammals (Third Edition), 2018

III Joints and Foramina

Skull bones can meet in several ways and attach to each other by more than one type of material (e.g., cartilage and other connective tissue). Joints between adjacent cranial bones are referred to as sutures or synchondroses. Sutures are fibrous joints between dermal bones; synchondroses are cartilaginous joints between endochondral bones. Sutures and synchondroses are regions of growth between individual bones; in adults they may also function to relieve stresses that are produced in the skull ( Gordon, 1988). At parturition, some joints provide the flexibility for a relatively large brain within the cranium to pass through a relatively narrow birth canal. In the illustration of the exploded manatee cranium (Fig. 6), the hatched regions represent joints or regions of overlap. Fig. 8 compares some of the joints of the dog skull with those of the manatee and dolphin skull. The type of joint generally reflects the mechanical forces acting on the adjacent bones. Different types of joint may be found between the same bones in different species; types may also be different in different parts of the same joint, probably to reflect differences in forces. Interlocking joints can absorb mechanical energy. Movable joints eliminate shearing forces. Butt joints can support little shear but are strong in compression. Squamosal or scarf joints allow more surface contact between adjacent bones and are stronger than simple butt joints. Some bone configurations affect the complexity of joints, and this complexity, in turn, affects the action and strength of the joints. The age of an animal can sometimes be determined by evaluating the sequence of ankyloses of sutures and synchondroses, as ankyloses occur in a consistent order (Moore, 1981).

Figure 8. Joint types in the cranium of the dog (A), manatee (B), and dolphin (C). Top row, diagrams of different joints; second and third row, dorsal and lateral views of skulls; bottom row, midline sectional view of cramium. Joints allow growth of adjacent bones, provide limited flexibility and absorb mechanical forces. Sutures are fibrous joints between dermal bones; synchondroses are cartilaginous joints between endochondral bones. Suture types are defined by their shape. PLA, plane or butt joint, an approximately straight suture with nearly squared-off margins. SQA, squamous or scarf joint, a suture with tapered overlapping margins. FOL, foliate joint, a suture with small alternating vertical bony plates, in which adjoining bones interleave. SER, serrate joint, an irregular suture, in which adjoining bones interlock. SYN, a synchondrosis with persistent cartilage between bones.

 Copyright S. A. Rommel.

The development of the skull bones proceeds at a pace different from that of the soft tissues of the head. Bone is remodeled throughout life; this takes place in response to trauma, nutrition, but is also part of normal development. This plasticity is reflected in the way individual skull bones form around vessels and nerves. The resulting openings, or foramina (singular, foramen), are often phylogenetically conserved. Therefore, they can be used to establish homologies of the same bones across different species. An individual nerve or blood vessel may be completely surrounded by a bone or bones of the skull, resulting in a specific foramen. Because this process occurs early in the development of the individual and appears to be similar in all vertebrates, cranial nerve foramina can be used to identify the skull bones. In Fig. 9, cranial nerves are indicated with Roman numerals (II, III, IV, V2, V3, VI, VII, IX, X, XI, XII), next to the figure label of the foramen that they emerge from. Nerves not mentioned (I, V1, VIII) are not visible in these views.

Figure 9. Comparison of the basicranial morphology of the manatee (A), dolphin (B), and dog (C). Als, alisphenoid; Boc, basioccipital; Bsp, basisphenoid; Exo, exoccipital; fis, fissure; for, foramen; Jug, jugal; L, left; Max, maxilla; Pal, palatine; Pmx, premaxilla; proc, process; Pty, pterygoid; R, right; Sqa, squamosal; Tym, tympanic; Vom, vomer. Roman numerals indicate cranial nerves that pass through the foramen or fissure indicated.

 Copyright S. A. Rommel.

In some species, or even in individuals of the same species of different ages, instead of a single foramen for each individual nerve, one or more nerves may exit the braincase through a single opening. Some openings are very large and irregular and are referred to as hiatuses. The cranial hiatus of the dolphin (Fraser and Purves, 1960) and manatee may include the following nerve openings: optic foramen (for cranial nerve II), orbital fissure [anterior lacerate foramen, for cranial nerve III, IV, V1, V2, and VI)], and oval foramen (V3). Such a cranial hiatus is not present in the other marine mammals.

The tympanic and periotic bones of the ear region are often referred to as the earbone complex or the tympano-periotic complex. The earbone complexes of the manatee and dolphin have loose connections with the rest of the skull bones, presumably to produce an acoustic isolation from the rest of the skull; in cleaned skulls the earbone complexes may fall out of the skull in these taxa. In life, the odontocete tympanoperiotic is surrounded by (airfilled) peribullar sinuses that add to this acoustic isolation (Fraser and Purves, 1960; Houser et al., 2004).

The mandible also has a number of foramina. At its caudal end, the medial side (lingual surface) of the dentary has a mandibular foramen, which is the opening of the mandibular canal for the alveolar vessels and nerves. In manatees, the mandibular foramen is relatively large because of the large amount of soft tissues and perioral bristles of the chin supplied and innervated via the mandibular canal. In dolphins, the mandibular foramen is even larger; it is referred to as a hiatus (Fraser and Purves, 1960). This foramen is giant in odontocetes, and the odontocete dentary is almost hollow and is filled with a well-vascularized mandibular fat body, which performs the acoustic function of receiving and guiding sound energy to the earbones (Norris and Harvey, 1974; Koopman et al., 2006).

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Skull

Friderun Ankel-Simons , in Primate Anatomy (Third Edition), 2007

Lorisidae

The skulls of Lorisidae, compared with those of other prosimians, give the impression of being dorsoventrally flat, especially in species of genera Perodicticus and Nycticebus. The interorbital distance is generally smaller in Lorisidae than in Malagasy Lemuridae or Indriidae. This narrowness is also seen in lorisids in the lessened postorbital breadth of the skull, or "postorbital constriction." Moreover, among lorisids the snout does not taper toward the front as much as in Lemuridae and thus gives the impression of being less long and pointed comparatively. Among lorisines, the nasal bones are flatter than in Lemuridae. A characteristic elongation of the snout beyond the front end of the tooth row is found in species of the two lorisid genera Arctocebus and Loris. This phenomenon is brought about as a result of their comparatively large premaxillae, the upper margins of which project forward. The nasal bones also enter this projection, thus forming a pipelike nasal opening. In addition, the snout is narrow in Arctocebus and Loris. In Nycticebus, the occipital is flattened and faces backward. The foramen magnum opens most directly backward in Nycticebus of all Lorisidae. Skulls of galagids resemble those of lorisids, but slight differences can be detected. For example, with galagids the cranial vault is slightly more rounded than in Lorisidae, and the interorbital distance is somewhat wider. The postorbital constriction, however, is much more marked in Galagidae than in Lemuridae. The small lacrimal bone at the lower inside corner of the orbit extends considerably forward onto the outside of the orbital wall, and the lacrimal canal (tear duct) is positioned externally. Figure 5.16 shows the skull base of a loris genus Perodicticus.

Figure 5.16. Skull base of a loris genus Perodicticus showing basicranial foramina. 1) Foramen incisivum; 2) f. palatinum major; 3) f. palatinum minus; 4) foramen ovale; 5) foramen lacerum; 6) f. postglenoideum; 7) Tuba auditiva; 8) Meatus acousticus externus; 9) f. condyloideum; 10) f. jugulare; 11) f. caroticum.

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Skull

Tim D. White , ... Pieter A. Folkens , in Human Osteology (Third Edition), 2012

4.2 Elements of the Skull

The term "skull" is often misused in common speech. Terms such as this have very specific meanings to anatomists and osteologists. It is worthwhile to review the proper use of terminology.

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The skull is the entire bony framework of the head, including the lower jaw.

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The mandible is the lower jaw.

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The cranium is the skull without the mandible.

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The calvaria (or calvarium) is the cranium without the face.

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The calotte is the calvaria without the base.

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The splanchnocranium is the facial skeleton.

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The neurocranium is the braincase.

The three basic divisions of the endocranial surface at the base of the neurocranium correspond to the topography of the base of the brain. These anterior, middle, and posterior cranial fossae are respectively occupied by the frontal lobes, temporal lobes, and cerebellum of the brain.

When the ear ossicles (three pairs of tiny bones associated with hearing) are included and the hyoid excluded, there are usually 28 bones in the adult human skull. Distinguishing these bones is occasionally made difficult because some of them fuse together during adult life. For this reason, it is advisable to begin study with young adult specimens, in which the bones are most readily recognizable. In addition to the 28 normal skull bones, there are often sutural bones (also called Wormian bones, or extrasutural bones), which are irregular ossicles that occur along some sutures. A large, triangular inca bone is occasionally found at the rear of human crania.

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SKULL

Tim D. White , Pieter A. Folkens , in The Human Bone Manual, 2005

7.3 Growth and Architecture, Sutures and Sinuses

At birth the skull is made up of forty-five separate elements and is large relative to other parts of the body. The facial part of the newborn skull, however, is relatively small, reflecting the dominance of brain development at this stage of maturation. The face "catches up" to the neurocranium as development, particularly in the mandible and maxilla, proceeds. Important stages in the development of the skull include emergence of the first set of teeth (between the ages of 6 and 24 months), the emergence of the permanent teeth (beginning at about 6 years), and puberty. Figure 7.7 illustrates growth of the skull.

Figure 7.7. Growth in the human skull. (Left, below, and opposite) Note the change in proportions of face and vault through the series. All specimens are shown in facial and lateral views. One-third natural size.

At birth the skull contains intervals of dense connective tissue between plates of bone. These "soft spots," or fontanelles, are cartilaginous membranes that eventually harden and turn to bone. In the adult the skull bones contact along joints with interlocking, sawtooth, or zipper-like articulations called sutures. Cranial articulations in the adult human skull are summarized in Figure 7.8. Many of these sutures derive their name directly from the two bones that contact across them. For example, zygomaticomaxillary sutures are sutures between the zygomatics and maxillae, and frontonasal sutures are short sutures between the frontal and nasals. Some sutures have special names. The sagittal suture passes down the midline between the parietal bones. The metopic suture passes between unfused frontal halves and only rarely persists into adulthood. The coronal suture lies between the frontal and parietals. The lambdoidal suture passes between the two parietals and the occipital. Squamosal sutures are unusual, scale-like, beveled sutures between temporal and parietal bones. The sphenooccipital, or basilar suture (actually a synchondrosis) lies between the sphenoid and the occipital. Parietomastoid sutures pass between the parietals and the temporals, constituting posterior extensions of the squamosal suture. Occipitomastoid sutures pass between the occipital and temporals on either side of the vault.

Sinuses are void chambers in the cranial bones that enlarge with the growth of the face. There are four basic sets of sinuses, one each in the maxillae, frontal, ethmoid, and sphenoid. These sinuses are linked to the nasal cavity and, in life, irritation of their mucous membranes may cause swelling, draining, and headache-related discomfort.

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Tumors of the Nervous System

Richard A. LeCouteur , Stephen J. Withrow , in Withrow & MacEwen's Small Animal Clinical Oncology (Fourth Edition), 2007

Radiography

Plain skull radiographs are of limited value in the diagnosis of a primary brain tumor; however, they may be helpful in detecting neoplasms of the skull or nasal cavity that involve the brain by local extension. Occasionally, lysis or hyperostosis of the skull may accompany a primary brain tumor (e.g., meningioma of cats), or there may be radiographically visible mineralization within a neoplasm ( Figure 29-2). 1,74 General anesthesia is required for precise positioning of the skull for radiographs, and various projections have been recommended to identify abnormalities. 1

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Metastatic Disease of the Nervous System

Rebecca A. Harrison , ... Franco DeMonte , in Handbook of Clinical Neurology, 2018

Anatomy

The skull base forms the floor of the cranium, and serves as a passageway for the spinal cord, cranial nerves, and cerebral vasculature. The ethmoid, sphenoid, occipital, paired frontal, and temporal bones constitute the skull base, which is subdivided into the anterior, middle, and posterior cranial fossa ( Policeni and Smoker, 2015). An indepth knowledge of the nerves and surrounding structures is essential to understand the clinical syndromes associated with lesions in this location. The frequency of SBM in the various anatomic regions of the skull base is presented in Table 14.4.

Table 14.4. Anatomic location of cranial base metastases referred for surgery: the MD Anderson experience

Anatomic location Proportion of patients (%)
Anterior fossa
Orbit
Frontal/ethmoid sinuses
Orbit and frontal/ethmoid sinuses
Planum and frontal/ethmoid sinuses
26
11
11
4
Anterior and middle fossa
Sphenoid wing and orbit
15
Middle fossa
Sella/parasellar region
Parasellar extending to cavernous sinus
Sphenoid wing/infratemporal fossa
15
4
11
Posterior fossa
Cerebellopontine angle
4

Adapted from Chamoun RB, Suki D, DeMonte F (2012) Surgical management of cranial base metastases. Neurosurgery 70: 802–809; discussion 809–810.

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Neuroimaging Part I

Hillary R. Kelly , Hugh D. Curtin , in Handbook of Clinical Neurology, 2016

Abstract

Skull base imaging requires a thorough knowledge of the complex anatomy of this region, including the numerous fissures and foramina and the major neurovascular structures that traverse them. Computed tomography (CT) and magnetic resonance imaging (MRI) play complementary roles in imaging of the skull base. MR is the preferred modality for evaluation of the soft tissues, the cranial nerves, and the medullary spaces of bone, while CT is preferred for demonstrating thin cortical bone structure. The anatomic location and origin of a lesion as well as the specific CT and MR findings can often narrow the differential diagnosis to a short list of possibilities. However, the primary role of the imaging specialist in evaluating the skull base is usually to define the extent of the lesion and determine its relationship to vital neurovascular structures. Technologic advances in imaging and radiation therapy, as well as surgical technique, have allowed for more aggressive approaches and improved outcomes, further emphasizing the importance of precise preoperative mapping of skull base lesions via imaging. Tumors arising from and affecting the cranial nerves at the skull base are considered here.

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Musculoskeletal System

John E. Cooper , in Gorilla Pathology and Health, 2017

Skull

Skulls predominate in museum collections – see Part II, A Catalogue of Preserved Materials. Some include both the cranium (calvarium and facial bones) and the mandible (referred to as 'skull' in Part II: A Catalogue of Preserved Materials); others lack the mandible.

Skulls/crania have played a large part in osteological, palaeontological, pathological and odontological studies in gorillas. Osteometry (usually a series of cranial measurements) is important in taxonomic and diagnostic research (see studies on 'Guy' in Appendix 5: Case Studies – Postmortem Investigations). Geometric morphometrics has been employed extensively in primate studies, especially of the cranium and mandible.

Some specific pathology relating to the skull is discussed later.

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Volume 2

Shirley I. Stiver , in Schmidek and Sweet Operative Neurosurgical Techniques (Sixth Edition), 2012

Conclusions

Skull base trauma implies transfer of significant forces to the cranium. Fractures of the skull base are often remote from the site of impact. The presence of a skull base fracture should heighten awareness for the possibility of associated cervical spine instability, cranial nerve deficits, vascular injury, and CSF fistula. Because of the location and extent of damage, operative repair of skull base injury requires subspecialized approaches and skills. Surgical repair is complex and often carries significant risk of hemorrhage from major arteries or venous sinuses. Advanced TBI monitoring and medical management in the ICU, together with expertise in a diverse repertoire of surgical approaches and techniques, are critically important to enable optimal recovery for patients with skull base trauma.

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Neuroimaging Part II

Thierry A.G.M. Huisman , Andrea Poretti , in Handbook of Clinical Neurology, 2016

Skull mechanical properties

The pediatric skull differs from the adult skull in many ways. It is unique because of a combination of higher plasticity and deformity, and consequently, forces are absorbed in a very different way compared to adults. Open sutures may function as "joints," allowing for a certain degree of movement in response to a mechanical stress ( Ghajar and Hariri, 1992). Open sutures also prevent early and rapid rise of the intracranial pressure related to mild brain swelling and space-occupying lesions. This feature can prevent or limit secondary brain injuries due to the various types of brain herniation. The pediatric skull base is also different compared to the adult skull base. The pediatric petrous bone is compact at an early age, which results in a high mechanical stress between the dense petrous bone and the soft/cartilaginous skull base and skull when exposed to traumatic forces. Absorption of forces is different in adults, in whom the difference in densities between the petrous bone and the skull base/skull is less prominent.

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