1-Is it a bone?
The first and foremost thing that a forensic anthropologist needs to confirm is whether the given substance is a bone. It has been found in numerous cases that bones have often been confused with ivory, stones or celluloid material. To jump into further investigation a forensic anthropologist should first carry out scrutinization concerning bone’s origin. These may include:
- Visual examination of surface for the presence of parallel striations, exfoliation, chipping
- Long bones have a hollow shaft
- Visual examination for shape
- Examination under magnifications
2-Bone origin: Human or Animal
After confirming whether the suspected specimen is bone, the next question that arises is whether the bone is that of a human or an animal. The specimen procured, if present, in its whole form can give substantial evidences of its origin, but not always. Human bones have been found to resemble many animals in terms of their shape and size. The case becomes more complicated in case when the bone specimens are not of human adult. It has been found that bones of a child, as they are unfused, do not match with that of human adult. Instead, they are quite similar to that of animals. Thus, determination of bone’s origin is the next big challenge that forensic anthropologists face.
Human and non-human bones exhibit a wide range of dissimilarities when examined carefully. These differences are due to:
- Variability in functions and role that a bone plays depending upon the species of organism
- Evolution is another significant factor. Human bones have undergone various changes over the period of time as humans have evolved through the ages
- Mode of living-terrestrial, aquatic, aerial etc.
- Mode of nutrition
- Species type: as different species have different shape, size and number of bones
The features that are used to distinguish human and non-human bones can be broadly studied under three categories:
- Gross anatomical features: they include shape, size and number of bones
- Macroscopic features: visible characteristics of bone
- Microscopic features: microscopic examination of cross-sections and histological differences
Gross anatomical features
|Skull vault||Larger, relatively smooth||Smaller, pronounced muscular makings|
|Orbits||Anteriorly placed||Laterally placed|
|Nasal region||Smaller, long and narrow||Larger and massive|
|Coronoid process of mandible||Almost vertical||Curved|
|Foramen magnum||Inferiorly placed and in the center||Posteriorly placed due to quadruped nature|
|Occipital bone||Small and less rugged||Large and rugged|
Picture 1: Human skull vs Pig skull vs Horse skull.
Picture 2: Human (biped) skeleton vs Dog (quadruped) skeleton.
|Type||Omnivores||Herbivores, carnivores and omnivores|
|Dental formula||2123/2123||3142/3143(dog), 3143/3143(horse),3142/3142(bear),3143/3143(pig)|
|Incisors||Largest maxillary incisors||Not so large, except in herbivores which have large incisors|
|Canines||Canines are small and less pointed||Big and pointed, except in herbivores|
|Premolars and molars||Small and cusped||Carnivores have sharp and less pointed premolars while herbivores have broad and flat molars and premolars|
Picture 3,4: Human vs Dog dentition
|General structure||Large, broad and flat||Smaller, convex on one side and concave on the other|
|Sacrum||Triangular, composed of 5 fused vertebrae||long and narrow, with fewer fused vertebrae; 3-4|
|Spinous process||Short; 2-3 inches||Long; greater than 6 inches|
Picture 5: Human vs Non-human spine.
4-Scapula and Clavicle
|Shape||Triangular||Rectangular and elongated|
|Scapular spine||Perpendicular to long axis||Parallel to long axis|
|Glenoid fossa||Present along most lateral surface||Present at the end of long axis|
Picture 6,7: Dog scapula vs Human scapula.
|Size and depth||Shallow and broad||Deep and narrow|
|Ribs||Relatively curved||Relatively straightened|
|Length||Due to biped nature, forelimbs are shorter than hindlimbs||Forelimbs and hindlimbs are of almost equal lengths due to quadruped nature|
|Strength and surface||Less strong, less heavy and have less rugged bony surface||Heavy, strong and massive, highly rugged bones|
|Radius-ulna||Occur as separate bones||Mostly occur as fused bones|
|Deltoid tuberosity||Not so prominent||Large and very prominent|
|Shape and size||Short and broad to wear upper body weight||Long and narrow|
|Sacrum||Short and broad||Long and narrow|
|Juvenile pelvis||Unfused||Mostly fused|
Picture 8,9: Dog Pelvis vs Human Pelvis.
|Femur||Single linea aspera, non-adult humans have unfused epiphyses||Double linea aspera, non-adult may have fused epiphyses depending upon type of locomotion|
|Tibia-fibula||Occur as separate bones||Mostly fused|
|Tibia cross-section||Triangular||More rounded|
9-Thumbs and foot
|Foot size and shape||Long and narrow||Short and broad|
|Density of bone||Lower||Higher|
|Porosity||Relatively more porous||Less porous|
|Compact bone||Compact bone is not much thick as compared to trabecular bone||Compact bone is relatively thicker|
|Trabecular cells||Trabecular cells are more in concentration as compared to cortical cells||Cortical cells have a higher concentration than trabecular cells|
Determining whether a bone is human or non-human is often coupled with microscopic examination to improve the accuracy of results. Before studying the microscopic features of a bone, we must know about the histology of bone tissue i.e. bone structure at microscopic level.
Bones are basically composed of two components- bone tissue and extracellular matrix. The extracellular matrix of bone is composed of water (15%), collagen fibers (30%), mineral salts in crystalline forms (55%) which include Ca3(PO4)2 and Ca(OH)2. These salts combine to form hydroxyapatite [Ca10(PO4)6(OH)2]. These crystals lateral combine with others salts and ions like that of Mg2+, K+, (SO4)2-. Collagen fibers present in the matrix form a mesh network between which all the salts and minerals are deposited and crystallize, a process called calcification. The strength of bone is determined by the intensity of calcification and its flexibility is defined by the collagen fibers present in there.
The bone tissue comprises four types of cells:
- Osteogenic cells: These are mesenchymal stem cells that differentiate into osteoblasts. They are the only type of bone cells capable of cell division. They are found in the inner lining of haversian canals, endosteum, and inner region of periosteum.
- Osteoblasts: These are the bone cells that secrete extracellular matrix called osteioids comprising collagen.
- Osteocytes: Osteoblasts surrounded by extracellular matrix are called osteocytes. They are responsible for exchange of nutrients and metabolic activities of the bone.
- Osteoclasts: Osteoclasts are differentiated macrophages. They are present in the inner portion of endosteum. Osteoclasts have a fibrous border facing bone surface. They release lysozymes that dissolve compact and spongy bone tissue during normal resorption process occurring during bone repair.
2-Compact Bone Tissue
The compact bone tissue as the name suggests is hard and strongest tissue of the bone. It is generally present on those areas which experience considerable amount of pressure e.g. diaphysis of long bones. It can be histologically described as follows:
- Composed of repeating structural units called osteons, that occur in cylindrical forms, present parallel to each other to the vertical axis of bone
- Each osteon is composed of a network of lamellae present in the form of concentric rings with a hollow canal at the center called haversian canal, through which blood vessels, nerves and lymphatic vessels pass
- Lamellae are nothing but calcified extracellular matrix
- Between the concentric rings of lamellae are empty spaces called lacunae. These lacunae contain osteocytes and have radiating canals in all directions called canaliculi filled with extracellular fluid
- Canaliculi of different lacunae are interconnected and also connected with the haversian canal that allows exchange of substances
- The areas between osteons are called interstitial lamellae which are nothing but old and worn out osteons
- The outer membrane lining the bone is called periosteum under which are the outer circumferential lamellae adhered to periosteum by Sharpe’s fibers
- Periosteum has transverse canals called Volkmann’s canals through which blood vessels, nerves and lymphatic vessels from the periosteum connect with those of haversian canal
- A network of lamellae lines the medullary cavity of the bone, they are the inner circumferential lamellae
Picture 10: Arrangement of osteons in compact bone tissue.
Picture Reference : Source
3-Spongy Bone Tissue
Spongy bone tissue is a relatively softer tissue as compared to compact tissue. It has lower density and is much more porous. It is always present inside a protective covering of compact tissue as in the epiphyses of long bones. It houses bone marrow tissue. It can be described as follows:
- Unlike the compact bone, lamellae in spongy bone tissue are randomly arranged in form of trabeculae
- Between the trabeculae are large spaces filled with bone marrow, these spaces have a rich supply of blood vessels
- Each trabecula contains concentric rings of lamellae, spaces called lacunae that enclose osteocytes. These lacunae have radiating canals called canaliculi
- Trabeculae of spongy bones are arranged along the line of stress to absorb and transfer stress without breaking
Picture 11: Enlarged section of spongy bone tissue.
4-Microscopic differences in bone histology (Humans vs Non-humans)
|Mean diameter of haversian canal in µm (maximum)||68.73||45.12 (horse), 42.56 (ox), 36.18(pig), 34.42 (dog)|
|Mean diameter of haversian canal in µm (minimum)||47.15||29.37 (horse), 30.99 (ox), 26.23 (pig), 21.11 (dog)|
|Mean diameter of osteons in µm (maximum)||263.91||238.50 (horse), 238.46 (ox), 232.26 (pig), 151.59 (dog)|
|Mean diameter of osteons in µm (minimum)||206.44||183.74 (horse), 181.49 (ox), 180.72 (pig), 117.15 (dog)|
|Mean number of osteons/mm2||4.00||14.06 (horse), 9.61 (ox), 7.00 (pig), 25.58 (dog)|
- Nutrient foramina
|Mean length of nutrient foramina of femur (mm)||28.4||14.7 (pig), 5.0 (sheep)|
|Mean length of nutrient foramina of humerus (mm)||37.2||8.2 (pig), 12.1 (sheep)|
|Mean diameter of nutrient foramina of femur (mm)||3.9||5.7 (pig), (2.6 (sheep)|
|Mean diameter of nutrient foramina of humerus (mm)||3.7||2.7 (pig), 2.2 (sheep)|
|Mean circumference of nutrient foramina of femur (mm)||8.2||8.5 (pig), 7.3 (sheep)|
|Mean circumference of nutrient foramina of humerus (mm)||8.8||6.8 (pig), 4.3 (sheep)|
|Mean foraminal index of femur (%)||38||27 (pig), 26 (sheep)|
|Mean foraminal index of humerus (%)||59||59 (pig), 56 (sheep)|
*foraminal index is the ratio of the distance between the superior end of the bone and the nutrient foramina multiplied by 100 to the total length of the bone.
1-www.e-pgpathshala.com, Paper no.7 (forensic anthropology), Module 9.
2-Principles of Anatomy and Physiology, Gerard Tortora and Bryan Derrickson.
3-Petra Urbanova, Vladimir Novotny, Distinguishing Between Human and Non-Human Bones: Histometric Method For Forensic Anthropology, Anthropologie, XLIII/1, pp. 77-85, 2005.
4-Beckett S. et al., Differentiating human versus non-human bone by exploring the nutrient foramen: implications for forensic anthropology, Int J Leg Med, DOI: 10.1007/s00414-017-1662-y, 2017, Springer.