Forensic Identification: Skeletal, Racial, and Sexual Dimorphic and Sternal Indices Analysis

Forensic Identification and Corpus Delicti

• Corpus Delicti

  • Definition: The "Body of offence."
  • It represents the essence of a crime and encompasses everything related to the crime itself.

• Criteria for "Unknown" Status

  • If identification of a dead body is not successful within a period of $48\,\text{hours}$, the body is officially declared as "unknown."
  • This protocol is mandated as per the Delhi Anatomy Act.

Racial Identification and Skeletal Indices

• Measurement Tools

  • Osteometric Board: Specifically used to measure bone length to identify race.
  • Vernier Calipers: Specifically used for measurements related to the Cephalic index.

• Crural Index (Tibio-femoral index)

  • Formula: $\frac{\text{length of tibia}}{\text{length of femur}} \times 100$
  • Leptorrhine (Caucasoids): Index value $< 70$
  • Mesorrhine (Mongoloids): Index value $70 - 85$
  • Platyrrhine (Negroes): Index value $> 85$

• Brachial Index (Radio-humeral index)

  • Formula: $\frac{\text{length of radius}}{\text{length of humerus}} \times 100$

• Intermembral Index

  • Formula: $\frac{\text{length of radius} + \text{humerus}}{\text{length of tibia} + \text{femur}} \times 100$
  • Relation: $\frac{\text{Brachial index}}{\text{crural index}} \times 100$

• Nasal Index

  • Formula: $\frac{\text{width of nose}}{\text{height of nose}} \times 100$

• Cephalic Index

  • Formula: $\frac{\text{Maximum breadth of skull (cm)}}{\text{maximum length of skull (cm)}} \times 100$
  • Classification:
    • Dolico-cephalic (
    • Mesaticephalic (75 - 79.9): Indians, Chinese, and Europeans.
    • Brachycephalic (80 - 85): Mongoloids.

Dental Characteristics and Racial Traits

• Caucasoids

  • Characterized by Carabelli cusp on the first molar ($M_1$), which is an extra cusp located towards the inner surface.
  • Hair cross-section: Oval.
  • Palate: Triangular.
  • Orbits: Triangular.

• Mongoloids

  • Shovel-shaped incisors: Present as a concavity towards the inner surface of the teeth.
  • Taurodontism: Often described as a "Bull dog appearance" of the jaw. Features include apical displacement of the pulp cavity and an overall increase in pulp cavity size.
  • Enamel pearls: Ectopic location of enamel.
  • Hair cross-section: Round.
  • Palate: Round.
  • Orbits: Round.

• Negroes

  • Non-shovel shaped incisors: Normal enamel placement without the inner concavity.
  • Hair cross-section: Kidney-shaped.
  • Palate: Rectangular.
  • Orbits: Square.
  • Teeth typically show lateral displacement.

Sex Identification and Skeletal Variation

• Sexual Dimorphism

  • Variance between male and female skeletons.
  • During fetal life, only the pelvic bone is differentiable for sex determination.
  • Other bones only become differentiable after puberty.

• Krogman's Table (Accuracy of Skeletal Sexing)

  • All 206 bones: $100\%$
  • Pelvis and Skull together: $98\%$
  • Only Pelvis: $95\%$ (Highest accuracy for a single bone/region).
  • Only Skull: $90\%$
  • Only Long Bones: $80\%$

Skull Morphology for Sex Determination

• Commonality Table

  • In general, all parameters in the male skull bone are larger and more prominent compared to the female skull.
  • Exceptions (Larger in Females): Frontal and parietal eminences are more prominent; the nasal aperture is lower and broader.

• Female Skull Features

  • Prominent frontal and parietal eminences.
  • Rounded orbits and round forehead.
  • Rounded chin.
  • Nasal aperture is lower and broader.

• Male Skull Features

  • Prominent supraorbital ridge.
  • Large glabella and prominent naso-frontal angle.
  • Large mastoid bone.
  • Ridge over the auditory meatus is prominent.
  • Squarish chin.
  • Nasal aperture is high and narrow.

• Mandibular Angles

  • Anatomical Angle: Used for sex determination. In females, this angle is $> 125^{\circ}$ to maintain the roundness of the chin.
  • Medicolegal Angle: Specifically used for age estimation rather than sex determination.

Sternal and Sacral Methods for Identification

• Sternum Analysis

  • Components: Manubrium ($M$), Body ($B$), and Xiphysternum ($X$).
  • Ashley's Rule (of 149): Combining the length of the manubrium and the body. If the total is $> 149\,\text{mm}$, it is likely Male; if $< 149\,\text{mm}$, it is likely Female.
  • Hyrtl's Law: Compares body length to manubrium length. If Body $> 2 \times M$, it is Male. If Body $< 2 \times M$, it is Female.
  • Sternal Index: Formula is $\frac{\text{length of } M}{\text{length of } B} \times 100$.

• Sacrum and Pelvic Attributes

  • Sacroiliac Articulation:
    • Male: Large, spanning $2.5 - 3$ vertebrae ($S_3$).
    • Female: Small, spanning $2 - 2.5$ vertebrae ($S_2 - 2.5$).
  • Curvature:
    • Male: Evenly distributed curvature.
    • Female: Only the lower half curves to allow for a large, wide pelvic outlet.
  • Kimura's Base Wing Index (Alar Index):
    • Formula: $\frac{\text{Width of wing}}{\text{Breadth of } S_1} \times 100$
    • Male: Approximate value is $65$.
    • Female: Approximate value is $80$ (Breadth of $S_1$ is generally greater in males).
  • Basal Index (Corpora Basal Index): Male value is $46.2$; Female value is $54.3$. Note that the Corpora basal index is cited elsewhere as $40$ for females in a comparative context.

Pelvic Sex Identification and Comparative Morphology

• General Rules for Pelvis

  • Most parameters are large and wide in females to facilitate childbirth.
  • Exceptions (Larger/More Prominent in Males):
    1. Obturator foramen (Large and oval in males; small and triangular in females).
    2. Sacroiliac joint articulation (Larger in males).
    3. Acetabulum (Larger in males).

• Pelvic Structural Comparison

  • Pelvic Inlet: Heart-shaped in males; Circular/Round in females.
  • Pelvic Cavity: Funnel-shaped in males; Round and broad in females.
  • Pelvic Outlet: Small in males; Large in females.
  • Subpubic Angle: V-shaped in males ($\approx 75^{\circ}$); U-shaped in females ($92^{\circ} - 100^{\circ}$).
  • Ischial Tuberosity: Inverted in males; Everted in females.
  • Greater Sciatic Notch: Small, narrow, and deep in males; Large, wide, and shallow in females.
  • Sciatic Notch Index (width/depth): $4 - 5$ in male fetuses; $5 - 6$ in female fetuses.
  • Pre-auricular Sulcus: Not prominent in males; Prominent and broad in females (where the anterior sacroiliac ligament attaches).

• The Chilotic Line

  • Definition: The line joining the ileopectineal eminence and the sacroiliac articulation.
  • In males, the posterior (sacral) segment is more prominent (extends to $S_3$).
  • In females, the anterior (pelvic) segment is more prominent (extends to $S_2 - 2.5$).
  • Chilotic Line Index (sacral/pelvic): $> 100$ in males; $< 100$ in females.
  • Washburn Index (Ischiopubic index): $\frac{\text{Pubic length}}{\text{Ischium length}} \times 100$. Values: Male ($73-94$); Female ($91-115$).

Questions & Discussion

• Question 1: A female skull brought by police was analyzed in a forensic department. To consider this a female skull bone, which features should be present?

  • Options: 1. Prominent Frontal & Parietal eminence, 2. Narrow mastoid, 3. Small, smooth glabella, 4. Square orbits, 5. Prominent cheek, 6. Round forehead.
  • Answer: C. Features 1, 2, 3, and 6 (Prominent F & P eminence, Narrow mastoid, Small/smooth glabella, Round forehead). Square orbits and prominent cheeks are typically associated with males or specific racial traits.

• Question 2: A male pelvis brought by police was analyzed in a Forensic department. To consider this a male pelvis bone, which features should be present?

  • Options: 1. Large obturator foramen, 2. Large sacroiliac joint surface, 3. Large acetabulum, 4. Subpubic angle - V shaped, 5. Ischial tuberosity everted.
  • Answer: A. Features 1, 2, 3, and 4 (Large obturator foramen, Large sacroiliac joint surface, Large acetabulum, V-shaped subpubic angle). Feature 5 is incorrect because everted ischial tuberosities are characteristic of the female pelvis.