Skeletal Series Part 7: The Human Arm

In this post we shall focus on the main bones located in the arm.  They are the Humerus, Radius & Ulna.  The previous post on the shoulder elements (Scapula & Clavicle) can be found here.  It should be noted that the bones discussed  in this post, known as the forelimb, are the homologs to the bones in the leg, the hind limb.

Articulation of arm with the distal humerus and proximal radius and ulna making the elbow joint (Image credit: Wikipedia 2011).

Excavation

As noted in previous Skeletal Series posts care should be taken with excavating human remains, and the maxim that ‘context is everything’ should be well noted with detailed plans of the in-situ remains made.  It is likely that some damage will have occurred to the smaller ulna and radius as they are more fragile then the larger and denser humerus bone.  A record of the condition of the bones should be made, alongside what contextual information is available (Mays 1999, White & Folkens 2005).

Arm Anatomy & Function

The humerus articulates proximally with the scapula and clavicle, as discussed in the last entry (See diagram below).  The distal humerus articulates with the proximal radius and ulna head.  This articulation makes up the elbow, which will be discussed in detail below.  At the distal end of the radius and ulna the carpals are located, which make up the wrist.  These, alongside the other elements in the hand, will be discussed in the next Skeletal Series post.

The individual brachium and antebrachium skeletal elements and major skeletal landmarks, as seen in articulation with the full limb (image credit: Wikipedia 2011).

The function of the forelimb is to provide a rigid limb to help hold, grab and move surfaces and objects.  The shoulder girdle and arm bones have moved away from our evolutionary history of weight-bearing limbs, and have become essential in helping humans to manipulate and move objects with astounding dexterity (Jurmain et al 2011).

Elbow Joint

The elbow joint (image credit: CK-12).

This joint in particular is important to understand as it is a key hinge joint.  The diagram below helps to mark out the distal humerus with the proximal radius and ulna in articulation.  The elbow is one of the strongest points of the body in terms of bone hitting strength.  The two main movements of the elbow are flexion and extension of the humerus and ulna, alongside the pronation of the radius and ulna in turning the arm over (White & Folkens 2005).  The joint itself has a large synovial membrane that protects the articulation points of the bone, whilst the main muscles involved are the Brachialis & Brachiaoradialus (at the anterior side) and the Triceps Brachii & Aconaeus towards the posterior side.  The lateral and medial muscles are the Supinator and Extensor muscles, alongside the Flexor muscles and Flexor Carpi Ulnaris muscles (White & Folkens 2005, but also here).

Anterior elbow joint in articulation, highlighting the major skeletal landmarks of the three bones that make up the joint. Image credit: here.

The Humerus

The humerus is the largest bone in the upper body, and ‘compromises of a proximal end with a round articular head, a shaft, an irregular distal end’ (White & Folkens 2005: 203).  It articulates with the Glenoid cavity (or fossa) of the scapula, and as mentioned, the proximal radius and ulna at the distal end.  The humerus head faces medially, whilst the surgical (or anatomical) neck is the groove that encircles the head for the attachment of the joint capsule (White & Folkens: 203-4).  Both the Greater and Lesser Tubercle are muscle attachment eminences that help move and rotate the upper arm.  On the Greater tubercle (the more posterior and large of the tubercles) rugosities for the insertion of the rotator cuff muscles are round, which help in rotation and adduction and abduction of the arm (White & Folkens 2005).

Main skeletal landmarks of the humerus (click to enlarge). Image credit: Google 2011.

The Shaft of the humerus is variably triangular in section, going from more cylindrical at its proximal end to more triangular in shape towards the distal end (Larsen 1997).  The Deltoid tuberosity is an important feature located on the lateral side of the shaft.  It is the insertion site of the deltoideus muscle, and is recognised by its roughened appearance.  Towards the distal end of the humerus we have several key features that are easily identifiable in recognising this as an upper limb element.

The Olecrannon Fossa is the largest of three hollows located posteriorly at the distal end, and accommodates the olecrannon process of the ulna during forearm extension.  The Capitulum is the rounded eminence that forms the lateral portion of the distal humeral surface, and it articulates with the head of the radius (White & Folkens 2005: 211).  The Lateral and Medial Epicondyle are the non articulating projections of bone, the medial is more prominent than the lateral epicondyle.

The humerus is relatively easy to recognise by the certain features picked out above, but parts can be confused with the tibia and femur.  With the femur, the head has a distinct depression called the Fovea Capitis whilst the humerus lacks this feature (Mays 1999).  The humeral shaft is smaller and less triangular than the tibial shaft.  When siding remember that the olecrannon fossa is posterior and the medial epicondyle is larger, and the humeral head faces medially.  The deltoid tuberosity is found laterally (White & Folkens 2005: 214).

The Ulna

The Ulna is the longest and thinnest bone of the forearm, and articulates proximally with trochlea of the humerus and head of the radius.  Distally, it articulates with the ulnar notch of the radius and an articular disk that separates it from the carpals.  The Olecrannon of the ulna is located on the most proximal part of the ulna; it is the insertion point for triceps brachii muscle.  The Trochlea Notch articulates with the trochlea articular surface of the humerus.  The Coronoid Process is the ‘anterior beak shaped projection at the base of the semilunar notch’ (White & Fokens 2005: 219).  The Radial Notch  is the small articular surface for the radius, and is located along the lateral side of the coronoid process.  The Radial Articulation (Ulna Head)  is the distal, lateral round articulation that conforms to the ulna notch on the radius.  The distal and proximal ends of the ulna are fairly distinctive and indicative of the element, however as White & Folkens (2005) and May (1999) point out, the shafts could be mistaken for radial or fibular shafts.

The ulna and the radius and their associated skeletal landmarks, click to enlarge. Image credit: Wikipedia 2011.

The Radius

The radius is a relatively small bone and shortest of the three in the forelimb.  Its name was gained for the action it goes through as the ‘turning movement about the capitulum of the humerus’ (White & Folkens 2005: 214).  At the proximal end it articulates with the humerus and medially with the ulna on both proximal and distal ends, whilst also distally it articulates with two carpal bones of the wrist.

The Head is a round articular structure at the proximal end of the radius, and as stated above articulates with both the humerus and ulna.  The Neck is a slender segment between the head and the radial tuberosity.  The Radial Tuberosity is a blunt rugged structure on the anteromedial site of the proximal radius that marks the insertion for the biceps brachii muscle (Mays 1999).  The  Styloid Process is a sharp projection located on the lateral side of the distal radius whilst the Ulnar Notch is a concave articular hollow on the medial corner of the distal radius.

Discussion: Wrist Fracture

Colle’s fracture is a break at the distal end of the radius and ulna that results in a ‘dinner fork deformity‘ with dorsal angulation, and displacement of the fracture with radial angulation.  The counterpart to this is Smith’s fracture which is the same but the fracture is displaced in the opposite direction, ie palmar (Marsland & Kapoor 2008: 96).

Smiths fracture highlighting the displacement of the distal radius. Image credit: Wikipedia 2011.

These type of fractures often occur because of trips or falls onto outstretched hands, as an automatic safety device by the body.  In modern contexts they also happen in a variety of sport environments.  These types of breaks are often easy to treat with splints and plaster casts, although they sometimes require surgery to correct the breaks and/or angles.  The patients can often be left with a visible deformity, but likely without any pain whatsoever (Marsland & Kapoor 2008: 96).  In archaeological examples these type of fractures can be found in any number of contexts or cultures.  It is important to note that, as Larsen (1997) says, many human cultures’ skeletal series often exhibit these breaks, and it can shed light into pathways of differing lifestyles.  Larsen also notes that whilst there is a large osteological literature on injuries in comparison to more population based studies which would help to highlight inferences on accidents and conflict in both historic and prehistoric societies (1997: 109).

Further Information

• A detailed diagram of the upper arm muscles can be found here and of the lower arm here.
• A helpful page for muscle names and motions can be found here.
• Further information on Colles’ Fractures can be found here.

Bibliography

Jurmain, R. Kilgore, L. & Trevathan, W.  2011. Essentials of Physical Anthropology International Edition. London: Wadworth.

Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human Skeleton. Cambridge: Cambridge University Press.

Marsland, D. & Kapoor, S. 2008. Rheumatology and Orthopaedics. London: Mosby Elsevier.

Mays, S. 1999. The Archaeology of Human Bones. Glasgow: Bell & Bain Ltd.

Roberts, C. & Manchester, K. 2010. The Archaeology of Disease Third Edition. Stroud: The History Press.

Waldron, T. 2009. Palaeopathology: Cambridge Manuals in Archaeology. Cambridge: Cambridge University Press.

White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic Press.

Broken Bones: One of My Own

An x-ray of my right tibia showing a traumatic transverse fracture in 2009.

My right tibia and fibula, with a transverse fracture gained in the summer of 2009.  A result of polyostotic fibrous dysplasia and my having MCune Albright Sydrome.  Needless to say I spent the summer reading in the sun.  The fracture took a remarkable 17 weeks to heal in a plaster cast.

Teesside Archaeology Excavation At Preston Park

For the past few days I have been on site volunteering for Tees Archaeology on one of their annual excavations at Preston Park Hall & Museum, near Stockton-on-Tees.  The excavation is continuing until a week Friday, so it is only a short two week run.

Preston Park Hall

The excavation is hoping to uncover the  original boundary lines, ditches and the partition distances of the heated greenhouses of the Preston Hall Kitchen Garden dating from 1857.  This information will then be passed on to those who are redesigning the kitchen garden ahead of renovation next year.

Preston hall was built between AD 1820-1825 by David Burton Fowler, and during the latter part of the 19th century ownership passed to Sir Robert Ropner.  Initially the Hall faced South across the River Tees but was later re-fronted to face the North side, possibly due to encroaching views from the Stockton and Darlington Railway.

At the site I am the finds processor; so I’m helping to clean the artefacts from the numerous trenches, mark and bag them for future study.  Its good to be back out in the open, and at the heart of a dig again after a long absence of  nearly 3 years from taking an active part in an excavation.

The material and artefacts themselves are typical of what you would normally find on such a site- clay ceramic pipes, ceramic building material, butchered animal remains, the odd marble, slag waste and numerous brick & slate tiles.  There are also numerous willow pottery fragments being found.  Interestingly the diggers have uncovered an articulated sheep skeleton, with other possible animals underneath near the centre of the garden.  So far the diggers have also uncovered two medieval pottery fragments.

Willow Pottery

There are a number of events still to come in 2011 from Tees Archaeology so if you are in the area or interested please don’t hesitate to come along and join in.  In this day and age it is important that we support our local archaeological units throughout a time of harsh cuts that threaten our shared heritage.

Skeletal Series Part 6: The Human Shoulder

This post will focus on the scapula and the clavicle elements of the shoulder girdle.  The scapula provides the back of the shoulder, and the clavicle articulates with the sternum (discussed in previous post) and the top of the arm (the humerus).  The humerus will be discussed in a subsequent post on the elements of the arm.

Excavation

Together with previous posts on the spine and rib cage, this post makes up the ‘trunk’ of the human body.  As ever, care should be taken during excavation & examination.  Both the scapula and the clavicle are fairly tough elements and survive well.  The body and medial border of the scapula is liable to damage however as it is a thin blade of bone (Mays 1999).

On mainland Europe the study of anthropologie de terrain (the study and alignment of the body in a burial context) is often used, especially so in prehistoric sites.  Interestingly by examining the placement of the clavicle bones in burial, you can often tell whether a body has been covered in a shroud or likewise garment in the deposit of the cadaver.  The clavicles are often found near vertical in the upper chest cavity, which itself is often tightly bound.

The Shoulder Girdle Anatomy and Its Function

The shoulder girdle consists of the scapula bone, and the clavicle, which provide support and articulation for the humerus.  They also  anchor a variety of muscles which help rotate, move and flex the humerus.  The joint of the humerus and scapula is called the Glenohumeral Joint, the acromion process (see below) and clavicle is the  Acromioclavicular Joint, & the sternum and clavicle is called the Sternoclavicular Joint (Marshland & Kapoor 2008: 206).  The clavicle functions as the strut for the shoulder whilst the scapula helps provide anchor points for the larger muscles as well as the loose ranging ‘cup’ for the humeral head (White & Folkens 2005: 193).  Because of the lateral placement of the forelimb on the upper human body, we have evolved away from our nearest ancestors, as the forelimb placement gradually changed (See Afarensis article below in relation to our recent hominid brothers).  The diagram below marks out the main features of the shoulder girdle-

Anterior view of the shoulder elements, note only the clavicle and scapula are discussed in this post (Image credit: Britannic Inc 2007).

The clavicle is easy to palpate in your own body, along the length of the bone whilst the scapula spine and acromial process (see below) can be palpated just adjacent medially from the top of either arm.

Clavicle

As for any shoulder element, there are two clavicles present in the human skeleton.  As demonstrated by the above and below diagram, the clavicle is a tubular S shaped bone that sits anteriorly in the shoulder joint and is easily palpated.  The clavicle is oval to circular in cross section (White & Folkens 2005: 193).   The main anatomical landmarks are featured in the diagram below.

Landmark features and muscle attachment sites for clavicle (click to enlargen). Image credit: Wikipedia.

The costal impression is a broad rough surface that anchors the costoclavicular ligament, which strengthens the joint.  The lateral side of the clavicle has two major attachment muscle sites for the trapezuis & deltoideus muscles (White & Folkens 2005: 193).  The clavicle articulates with the acromial process of the scapula at the lateral end, whilst at the medial end it articulates with the clavicular notch of the manubrium.  The clavicle is often broken during a trip or a fall as the bone is so close to the skin, and acts as a supporting strut (Marsland & Kapoor 2008).

There are a few main points to consider when siding a clavicle.  The medial end is rounded whilst the lateral side is flattened.  Most irregularities are roughenings are on the inferior edge of the bone, whilst the bone itself ‘bows anteriorly from the medial end, curves posteriorly at the midshaft and sweeps anteriorly again at the lateral flat end’ (White & Folkens 2005: 195).

Scapula

The scapula is a ‘large, flat, triangular bone with two basic surfaces; the posterior (dorsal) and costal (anterior, or ventral)’ (White & Folkens 2005: 195).  The bone articulates with the humerus at the glenoid cavity (or fossa), and the distal clavicle on a small facet on the acromion process (see below diagram).  The ‘coracoid process just anteriorly and superlaterally from the superior border of the scapula’ whilst the acromion process is the lateral projection of the scapula spine.  Both of these projection points provide anchoring points for a number of key muscle abductors, rotators and flexors, amongst others (White & Folkens 2005: 200).  The glenoid cavity provides the humeral head with great mobility because of how shallow the fossa is; however the arm can be easier to dislocate then the leg bones (Marshland & Kapoor 2008).  The scapular spine provides an anchor point for the acromion process, and it key in distinguishing the posterior aspect of the body.

Distinctive landmark features on the scapula (anterior view, lateral view and posterior view). Image credit: Wikipedia.

Interestingly scapula fractures are rare in the archaeology record, but when evident they are usually located in the blade of the bone.  They are usually marks indicative of interpersonal violence due to the posterior position and location (Roberts & Manchester 2010: 104).  However as pointed out above the blade is usually damaged before or during excavation due to its delicate nature.

Another feature to be aware of is the lack of fusion that can take place at the acromion epiphysis (growing plate).  The most famous case concerning the lack of fused acromional points in a  skeletal series are from the remains of individuals from the Tudor ship The Mary Rose.  Of the skeletons studied, 13.6% of their number had unfused acromions (see diagram above/below).  The reason suggested was that they represented the archers aboard the ship, and had practised since childhood which had prevented any fusion of the element because of the constant stress, strain and movement needed to be a top bowman (Roberts & Manchester 2010: 105).

Posterior shoulder anatomy showing the major muscle (supra and inferspinatus muscles). Image credit: source.

When siding and investigating a piece of suspected scapula bone, it should be noted that it is mostly a thin bone, and unlike the pelvis, there is no spongy bone sandwiched between the cortices.  The following is taken from (yes that’s right!) White & Folkens 2005, page 202, with some modification.

• The glenoid cavity is teardrop-shaped, with the blunt end inferior.
• An isolated acromion is concave on its inferior surface.  The clavicular facet is anteriormedially relative to the tip.
• For an isolated coracoid element the smooth surface is inferior whilst the rough superior.  The anterior body is longer and thee hollow on the inferior surface faces the glenoid area.
• The spine thins medially whilst it thickens towards the acromion.  The inferior border has a tubercle that points inferiorly, as seen in the above diagram.
• On the posterior body there are several transverse muscle attachment sites.  These are usually quite prominent, and are key indicators in helping to visualise the orientation of the scapula.

Range Of Movement

Lateral view of the rotation of the shoulder joint. Image credit: Wikipedia.

Anterior view of the rotation of the shoulder joint. Image credit: Wikipedia.

An Arctic Case Study

There is a perception, garnered from the earlier descriptions of the Arctic aboriginal groups, that the native Eskimo groups were passive, of ‘quiet repose and lived in a state of non-violence’ (Larsen 1997: 131).  New bioarchaeological investigations are helping to provide data that is slowly leading to a revision in the review of those perceptions.

A Saunaktuk site, dated to the late 14th Century AD, located east of the Mackenzie Delta in the Canadian Northwest Territories has provided compelling evidence of violent confrontation between native groups (Larsen 1997).  As Larsen (1997: 132) discusses the skeletal remains of 35 Inuit Eskimo Villages represented at the site, it becomes clear that there is evidence for violent death and body treatment, which is indicated by extensive perimortem skeletal modifications.  A large percentage of the whole group are adolescents (68.6%), whilst all of individuals represented had not been purposefully buried.  It is suggested that the group represents a targeted selection whilst other adults where away from the site (Melbye & Fairgrieve 1994).

Studying the bones in anatomical position. Image credit: Google.

On the skeletons themselves, hundreds of knife cuts were evidenced.  These ranged from around the articular joints and neck vertebrae, which is indicative of decapitation and dismemberment (Larsen 1997).  As well as this there are numerous cuts on the facial bones on many of the victims, with cuts also present on the clavicles and scapulae as well (Melbye & Fairgrieve 1994).  Many of these cuts reflect an overall pattern associated with dismemberment, removal of muscle and other soft tissues as well as intentional mutilation.  There is the distinct possibility of cannibalism having been carried out at this site.

In particular, unique to this Saunaktuk skeletal series, is the ‘presence of gauges at the ends of long bones’ (Larsen 1997: 132).  The modifications of the gauges on the adult distal femora are consistent with oral tradition describing a type of torture where the victims knees were pierced and the individual dragged around the village by a cord passed through these perforations’ (Larsen 1997: 132).

We have to understand that there is a vast rich historical record that does help to provide a context for this group to group violence as recognised by the skeletal and oral records.  Violent interactions at this locality occurred between the groups, and intergroup violence has been recorded by many explorers for the Hudson Bay Company in the 18th century (Melbye & Fairgrieve 1994).  Other pre-contact sites such as Kodiak Island in Alaska, alongside the sites of Uyak Bay, Crag Point & Koniag Island there is also evidence of culturally modified human bone.  However, we must remember the context in which these actions had taken place.  There are a small selection of the overall number of ore-contact Arctic sites in this area.  Please refer back to previous posts by my guest blogger Kate Brown on the pre conditions and difficulties of diagnosing cannibalism.

Further Online Sources

• For detailed information on the muscles surrounding the shoulder joint, the 1st and 2nd part of this blog post has in depth knowledge on the muscle and bone elements and attachment sites.
• A short article dealing on breaking the clavicle and Lance Armstrong’s cycling accident.
• A fine post by Afarensis on the Homo Floresiensis & humeral torsion.

Bibliography

Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human Skeleton. Cambridge: Cambridge University Press.

Marsland, D. & Kapoor, S. 2008. Rheumatology and Orthopaedics. London: Mosby Elsevier.

Mays, S. 1999. The Archaeology of Human Bones. Glasgow: Bell & Bain Ltd.

Melbye, J. & S. I. 1994. ‘A Massacre And Possible Cannibalism In The Canadian Arctic: New Evidence From The Saunatuk Site (NgTn-1)’. Arctic Anthropology. Vol 31. No 2. PP 57-77. Wisconsin: University of Wisconsin.

Roberts, C. & Manchester, K. 2010. The Archaeology of Disease Third Edition. Stroud: The History Press.

Waldron, T. 2009. Palaeopathology: Cambridge Manuals in Archaeology. Cambridge: Cambridge University Press.

White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic Press.

Skeletal Series Part 5: The Human Rib Cage

As we covered the vertebrae in the previous post in the skeletal series, we shall move on to the last elements in the axial skeleton (bar the clavicle and scapula in next post).  The elements of the appendicular skeleton will follow shortly.

Excavation

As before, great care must be taken when excavating the ribs.  I have carried out micro-excavation of juvenile remains, (when I volunteered at Humber Field Archaeology) that consisted of the vertebrae, half of the ribcage and parts of the pelvis in-situ, and it took a while.  During excavation of human remains on site, it is very unlikely that the rib cage will be in its natural anatomical position.  Due to the soil and weight of the earth above the body, and the movement in the intervening period between burial and excavation, the ribs are likely to be broken and misplaced.  As always keep a look out for finer skeletal finds.

The Rib Cage

The focus of this post will be the sternum, which is made up of the Manubrium, Corpus Sterni (or Gladiolus) and the Xiphoid Process alongside a look at the ribs, all of which help to form the rib cage.  It is necessary to note here that variation in the number of ribs, as of the vertebrae discussed previously, can differ in people and in archaeological populations (Mays 1999: 15).  The function of the rib cage, as the main upper part of the torso in the human body, is to protect the vital organs that lie within the protective enclave of the ribs.  They include the majority of the torso organs such as the heart, liver, lungs, kidneys and partially the intestines.  The rib cage also helps breathing by the function of the intercostal muscles lifting and lowering the rib cage, aiding inhalation and exhalation.  The ribs are attached dorsally to the vertebrae, with articulating facets for the tubercle end of the ribs for the thoracic vertebrae (White & Folkens 2005).

Main anatomical elements of the rib cage. (Image credit: Wikipedia 2011).

Rib Cage Anatomy, Terminology and Elements

The number of ribs present in the typical human skeleton is of 12 paired rib elements (a total of 24 altogether). Ribs project from proximal articulating facets with thoracic vertebrae, slant forward, and depending on the rib pair under consideration, articulate at the distal end with either the sternum, hard cartilage or ‘float’ freely (Jurmain et al 2011).  Ribs usually increase from size from rib 1 to rib 7, and decrease in size from rib 7 to rib 12 (White & Folkens 2005: 185).

Posterior view of ribs and their articulating vertebrae partners. (Image credit: Wikipedia 2011).

The Upper 7 ribs on each side of the cage connect distally directly to the sternum via cartilage, whilst the 8th, 9th and 10th ribs connect indirectly to the sternum.  The last 2 ribs are often called ‘floating’ ribs because they have ‘short cartilaginous ends that lie free in sides of the body wall’ (White & Folkens 2005: 181).

The basic landmark anatomy of a rib includes the head, neck, tubercle which articulates with the thoracic vertebrae & the long shaft of the rib.  In the picture below the head of the ribs are medial whilst the sternal ends are lateral.  The side that is superior is called the cranial edge, whilst the inferior is called the caudal edge.  It can be fairly easy to side a loose or partial rib as the Cranial edge is fairly thicker and blunter when compared to the grooved and sharp caudal edge (White & Folkens 2005: 192).

The rib cage laid out from 1st to 12th ribs, note the size and shape morphology. Occasionally an individual will have only 11 paired ribs or may have an extra pair, this is natural variation. (Image credit: Shutterstock).

Distinctive Rib Cage Elements

• The 1st rib is most unusual and can usually be identified the easiest.  It is particularly blunt, broad and thick, as well as this it has no caudal groove (Roberts & Manchester 2010).

• The 2nd rib serves as an intermediary to the 1st and 3-9th more regular ribs.  It has a large tuberosity for the serrator anterior muscle half way along its length (White & Folkens 2005: 187).

• The 11th rib lacks a tubercle and the sternal end is often pointed.

• The 12th rib is shorter then the 11th rib and may be even shorter then the 1st rib.  It lacks the angle and costal groove, and is often easy identifiable (May 1999).

Sternum

As stated the sternum is made of 3 individual bones, those of the manubrium, corpus sterni and the Xiphiod Process.  As made clear by the diagrams below, there are 7 facets located laterally for the anterior of the ‘true’ ribs alongside the corpus sterni and manubrium.  The sternum is composed of these three elements in adulthood but develops from 6 segments (White & Folkens 2005: 181).

The manubrium is the thickest and squarest part of the sternum bones and should be easily identifiable as such.  At the superior corners there are clavicular notches located, which articulates with the right and left clavicles.  The clavicles and scapula help to form the shoulder girdle and will be discussed in the next post.

The three individual elements of the sternum, with the manubrium (proximal), corpus sterni (centre) and xihoid process (distal) highlighted. (Image credit: Wikipedia 2011).

Lateral view of sternum elements with the individual rib facets highlighted. (Image credit: Wikipedia 2011).

The corpus sterni is rather thin in comparison to the manubrium, and it is often said to be ‘bladelike’.  Again, costal notches are present as seen in the above picture.  They cater for ribs 2-7 (Mays 1999).

The xiphoid process can be found inferior to the corpus sterni but, depending on the age of the person involved, may not be found in archaeological samples.  The process shares the seventh costal notch.  This bone is often highly variable in shape, and is late to ossify (White & Folkens 2005: 184).

A Pre-contact Peruvian Case Study

The site of Pacatnamu, in the Jequetepeque River valley on the northern Peru coast, provides a site where mutilated human remains and contextual information has been unearthed (Larsen 1997: 137).  At this Moche site (100-800 AD), evidence has been found of executed captives who were thrown into a trench at the bottom of an entrance to a ceremonial precinct (Verno 2008: 1050).  The skeletal group found & studied was composed of 14 adolescent and young adult males, who were recovered from 3 superimposed layers at the site.  The superimposed layers were indicative of 3 distinct burial episodes (Larsen 1997: 137).  From the evidence on the skeletal elements, it seems that weathering took place after death but before burial.  The evidence is backed up by the palaeoenvironmental remains of the presence of the pupal cases of muscoid flies (Verano 1986).

Pacatnamu mass burial archaeological site and the second layer (Image credit: Verano 2008).

It seems that the display of the decomposing bodies, together with a lack of a proper burial, was clearly intentional.  In the topmost layer of the burial episodes, multiple stab wounds were found on both the vertebrae and rib elements.  This pattern is broken by the bottom and middle layer where the pattern is more towards decapitation or throat slashing as evidence by cutmarks on the cervical vertebrae (Larsen 1997: 137).  Of particular interest is the evidence of five individuals from the middle and lower deposits that have bisected manubriums with evidence of fractured ribs, which is suggestive of the chest cavity being opened forcibly (Verano 1986).

Larsen (1997: 137) remarks that on the ‘basis of the age distribution, sex, and evidence of healed and unhealed injuries (rib fractures, depressed cranial fractures), Verano (1986) speculates that they were war prisoners’.   The conclusion is well supported from the cultural representations in the art and architecture of the Moche culture.  Many cultures throughout the world made, and continue to make, sacrifices of various kinds; in particular it is thought that for pre-contact South American cultures human sacrifice represented ‘the most precious form of sacrifices, and seems to have been reserved for particularly important rituals and events’ (Verano 2008: 1056).

It has also been noted that the capture and killing of enemies was a common practise in communities in pre-contact South America.  Such killings can also incur within ritual presentations and displays.  There are many such examples throughout South American, and indeed throughout the Americas (Teotihuacan, Punta Lobos, Sipan) (Verano 1986).  A careful consideration through the integrated studies of the archaeological sites, bioarchaeological study of the human material, together with careful ethnographic comparisons, can help to understand the processes and results of human sacrifice in South American cultures.

Further Information

• This website here gives a quick and easy run down of the features of the rib cage.
• For a detailed look at how ribs and vertebrae articulate visit this site or this site.

Bibliography:

Jurmain, R. Kilgore, L. & Trevathan, W.  2011. Essentials of Physical Anthropology International Edition. London: Wadworth.

Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human Skeleton. Cambridge: Cambridge University Press.

Mays, S. 1999. The Archaeology of Human Bones. Glasgow: Bell & Bain Ltd.

Roberts, C. & Manchester, K. 2010. The Archaeology of Disease Third Edition. Stroud: The History Press.

Verano, J. W. 1986. ‘A Mass Burial of Mutilated Individuals at Pacatnamu‘. In C. B. Donnan & G. A. Cock. (eds.) The Pacatnamu Papers. 1. pp.117-138. Los Angeles: Museum of Cultural History, University of California.

Verano, J. W. 2008. ‘Trophy Head-Taking and Human Sacrifice in Andean South America‘. In H. Silvermann & W. Isbell.(ed.) Handbook of South American Archaeology. pp.1045-1058. Los Angeles: Springer.

White, T. & Folkens, P. 2005. The Human Bone Manual. London: Elsevier Academic Press.