Thieme Dissector Volume 3 (eBook)

Introduction

The head is the upper globular part of the body which contains the brain. The neck is an elongated, cylindrical region of the body which connects the head to the trunk.

The bones of the head and neck region consist of skull, cervical vertebrae, and hyoid bone.

1.The skull forms the skeleton of the head region.

2.The cervical vertebrae form the skeleton of neck region.

3.The hyoid bone is present in the upper part of the neck in front of the third cervical vertebra.

Skull

The skull is formed by many paired and unpaired bones (Table 1.1), most of which unite with each other by sutures. A suture is narrow, linear gap filled with dense, fibrous tissue. Students are suggested to identify various bones of a dry skull and intervening sutures with the help of Figs. 1.1 to 1.5. We may study the dry skull by looking at it from various aspects, that is, from above (superior view), behind (posterior view), front (anterior view), side (lateral view), below (external view of the base), and inside (internal views of the base and the skull cap).

Table 1.1 Bones of skull

The skull consists of a brain box/cranium and facial skeleton. The facial skeleton is located beneath the anterior part of the cranium.

Anatomical Position of the Skull

Anatomical position of the skull is obtained by keeping it in “Frankfurt horizontal plane.” This plane is obtained by holding the skull in such a way that the inferior border of the orbit and superior border of external acoustic meatus of right and left sides lie in the same horizontal plane.

Superior Aspect of the Skull

Bones: On the superior aspect of the skull, the scalp covers the parts of the frontal bone, right and left parietal bones, and occipital bone.

Sutures: With the help of Fig. 1.1, identify the coronal, sagittal, and lambdoid sutures in this view. The bregma is the meeting point between the coronal and sagittal sutures, while lambda is the meeting point between the sagittal and lambdoid sutures.

Bony features: Identify the parietal eminence, parietal foramen, temporal lines (superior and inferior), and vertex (highest point of the skull).

Posterior Aspect of the Skull

Bones: With the help of Fig. 1.2, look for the following bones on the posterior aspect of the skull: posterior portions of the parietal bones, upper part of the occipital bone, and mastoid parts of the temporal bone.

Sutures: Look for the following sutures seen in this view: lambdoidal suture, occipitomastoid suture, and parietomastoid suture.

Bony features: With the help of Fig. 1.2, identify the following bony features on a dry skull: external occipital protuberance, external occipital crest, highest nuchal lines (supreme nuchal lines), superior nuchal lines, and inferior nuchal lines.

Anterior Aspect of the Skull

The anterior aspect of the skull forms the facial skeleton. It consists of forehead, orbits, nasal region, and upper and lower jaws.

Bones: Identify the bones of the facial skeleton with the help of Fig. 1.3. These bones are the frontal bone, right and left nasal bones, right and left zygomatic bones, and right and left maxilla and mandible.

Sutures: Look at Fig. 1.3 for the following sutures present in this view: frontonasal suture, frontomaxillary suture, internasal suture, nasomaxillary suture, intermaxillary suture, frontozygomatic suture, and zygomaticomaxillary suture.

Bony features:

1.Forehead: Look for the following features on the forehead: glabella, superciliary arches, and frontal eminences.

2.Orbital opening: It is quadrilateral in shape and presents four margins: supraorbital, infraorbital, lateral, and medial.

3.Malar prominence: It is formed by the zygomatic bone and presents the zygomaticofacial foramen.

4.Anterior nasal aperture: It is piriform in shape. Note the presence of the median nasal septum, anterior nasal spine, and nasal notch of the right and left maxillae.

5.Upper jaw (maxillae): It is formed by the right and left maxillae. Note the bony features, such as the alveolar process, canine eminence, incisive fossa, and canine fossa.

6.Lower jaw (mandible): It is formed by the mandible. Note the features, such as alveolar process, mental foramen, symphysis menti, and mental protuberance.

Lateral Aspect of the Skull

Bones: This aspect of the skull is formed by the cranial and facial bones. Identify the following bones on the lateral aspect of the skull: frontal, parietal, occipital, nasal, maxilla, zygomatic, sphenoid, temporal, and mandible (Fig. 1.4).

Sutures: Many sutures, which are seen on this aspect, have already been observed while studying the superior, anterior, and lateral views of the dry skull. Hence, we shall study the sutures present in the central region of the lateral view (Fig. 1.4).

Identify an H-shaped suture present in the floor of the temporal fossa. This H-shaped suture is formed by the parietosphenoid, frontosphenoid, and temporosphenoid sutures. A small circular area enclosing this H-shaped suture is called a pterion. Also, identify the parietosquamous (squamous) and parietomastoid sutures, lambdoid suture, and occipitomastoid suture.

Bony features: Identify the superior and inferior temporal lines, zygomatic arch, supramastoid crest, external acoustic meatus, suprameatal triangle, mastoid process, and styloid process.

1.Temporal fossa: This fossa lies above the zygomatic arch. It is bounded above by the temporal lines. The temporal fossa communicates below with the infratemporal fossa.

2.Infratemporal fossa: It is an irregular fossa below the zygomatic arch and behind the maxilla. It communicates above with the temporal fossa deep to the zygomatic arch. It consists of the roof, anterior, medial, and lateral walls, while the posterior wall and floor are open.

3.Pterygopalatine fossa: The junction of the anterior and medial walls shows a fissure called pterygomaxillary fissure. Deep to the fissure lies the pterygopalatine fossa.

(Students should note that infratemporal and pterygopalatine fossae are not properly visualized in these figures. They should study these fossae on a dry skull with the help of their teacher.)

Base of the Skull

You should note that to visualize the base of the skull, it is necessary to detach the mandible from the rest of the skull. The base of the skull is formed, from anterior to posterior, by the maxillae, palatine, vomer, sphenoid, temporal, and occipital bones (Fig. 1.5). For the convenience of description, the base of the skull is divided into anterior, middle, and posterior parts by two imaginary horizontal lines. The first imaginary horizontal line is drawn along the posterior border of the hard palate, and the second line passes through the anterior margin of the foramen magnum.