By Elizabeth A. Murray, Mount St. Joseph University
When it comes to human anatomy and gender, there are differences between male and female skulls. On average, the bones of men are larger than women after puberty. Why is that? What makes their skull morphology so different? Read on to find out.
Male and Female Skulls
The reason why the bones of men are larger than women after puberty is owing to testosterone. As testosterone causes a longer period of bone growth, it also influences muscle mass, which can enlarge muscle attachment sites. So, following puberty, male skulls—as well as other bones—are generally larger and more robust, meaning they are more developed at their muscle attachment sites than those of females.
As a result, men often have larger brow ridges on their frontal bone, more robust zygomatic arches, larger mastoid processes and a rougher nuchal region where neck muscles attach.
Women retain the more gracile bony landmarks of their skull after puberty. So, they tend to have a smoother brow ridge, slight zygomatic arches, generally smaller mastoid processes, and a smoother nuchal region. This is not absolute; many of us are a blend of male and female skeletal characteristics, and the expression of each of them is on a continuum. The female jaw generally has a more obtuse mandibular angle, where the body meets the ramus, and a chin that typically comes to a single point in front. A male jaw frequently has a more 90° angle and often comes to two points anteriorly that tend to square off the mandible in front.
Forensic Anthropology
In addition, some of the geometry and bony landmarks of the mid-face region can be used in forensic anthropology in an attempt to assess a person’s ancestry or population affinity—which society may call their race. Features like the distances between the eye orbits, the width of the nasal aperture and shape of the nasal bones, the degree of projection of the upper and lower jaw—these can vary in people of different ancestries.
Measurements of those features, fed into computer software, can contribute to the biological profile of an unknown person—for example, whether they are male or female, and if their skull shows ancestral traits that may help get them identified by the medicolegal system.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
The Hyoid Bone
From the mid-face region, when we move inferior to the skull, we come to the hyoid bone. Though there is no gender difference indicated in the hyoid bone, it is still unique within the skeleton. This is because it is the only bone in the body that doesn’t directly articulate with another bone. That’s not to say the hyoid bone is completely free-floating. It is attached to the cartilages of the larynx, or voice box, that sits inferior to it and is also attached to muscles of the neck, but it doesn’t have a joint with any other bone.
The hyoid bone sits posterior and roughly parallel to the mandible. If we gently move the structures in our anterior neck from side to side for several seconds, we may begin to sense a pins-and-needles feeling at the base of our tongue. This is because the tongue is anchored to the hyoid bone. Due to its location, the hyoid bone is often fractured in cases of manual strangulation. Of course, a fractured hyoid doesn’t prove strangulation, but after bruising or other soft tissue evidence are decomposed, many pathologists find a fractured hyoid suggestive of strangulation, especially if it is the only broken bone in the skeleton.
Ribs
Next is the thoracic vertebrae. It is their companion—the ribs and the sternum—that form the complex known as the rib cage. There are twelve thoracic vertebrae, and each is attached to a pair of ribs. Ribs have their own anatomical landmarks: Beginning posteriorly, there’s the rib head, followed by a neck, and then a projection known as the tubercle. From the tubercle extends the shaft of the rib, which curves—in what’s known as the rib’s angle—as it passes from posteriorly to laterally and then anteriorly. On the inferior and deep or medial surface of the rib is the costal groove, in which intercostal nerves and vessels run. The sternal end of the rib is most anterior. That’s the anatomy of a typical rib, but not all ribs are created equally.
For one thing, the ribs start out shorter in length, then get longer, and ultimately shorten again. This results in a rib cage that is narrower superiorly and inferiorly and wider intermediately. The angles of the ribs also change in curvature through the rib cage. And while all ribs attach to the spine posteriorly, they do not all attach to the vertebral column in the same way.
False Ribs
In addition, not all ribs attach to the sternum anteriorly. The first seven pairs of ribs have their own costal cartilages that attach them to the sternum, so are called true ribs. But rib pairs eight, nine, and 10 usually borrow the cartilage of rib seven to reach the sternum, and rib pairs 11 and 12 don’t attach to the sternum at all. For this reason, pairs eight through 12 are known as false ribs, and pairs 11 and 12 are sub-grouped as floating ribs.
You may have read that floating ribs are their own third category, but there are technically seven pairs of true ribs, five pairs of false ribs, and of the false ribs, the last two pairs may be called floating ribs.
Common Questions about the Human Skull
The reason why the bones of males are larger than females after puberty is owing to testosterone. As testosterone causes a longer period of bone growth, it also influences muscle mass, which can enlarge muscle attachment sites.
The geometry and bony landmarks of the mid-face region can be used in forensic anthropology in an attempt to assess a person’s ancestry or population affinity.
The thoracic vertebrae, ribs, and sternum form the the rib cage.
