Fingerprint Pattern Identification & Whorl Tracing Notes

Pattern-Type Review & Course Road-Map

Morning office hours and evening scheduling conflicts delayed this lecture; goal today: finish ARCHES and, time-permitting, begin WHORL TRACINGS
World tracings essential for 2nd half of semester (Henry Classification); may postpone if time runs short but arches MUST be solid before midterm
Page references refer to course workbook (pp. 40–47)

Tempered-Card Key (Pg. 47) – Instructor’s Answer Set

Finger 1 (top card): Whorl → Plain Whorl (PW)
Finger 2: Ulnar Loop; ridge count $13$
Reminder on notation inside each finger box
• Loops → write u (ulnar) or r (radial) + ridge count in lower left corner
• Whorls → write w plus subtype (PW, CPW, DLW, AW)
• Whorl-tracing box (lower right corner) stays blank until tracings are covered
Ridge-count protocol (loops): draw line delta→core, count every ridge crossing the line, exclude delta & core themselves

Big-Picture Logic for Pattern ID

SEARCH FOR DELTAS first
• 0 deltas ⇒ some Arch
• 1 delta ⇒ some Loop
• ≥2 deltas ⇒ some Whorl
Then apply sub-classification rules (plain vs tented, ulnar vs radial, whorl subtype, etc.)

ARCHES (Pg. 40–46)

1. Plain Arch (PA)

Ridges enter from one side, rise in a smooth wave/“hill,” exit the opposite side
No deltas, cores, type lines
Visually the simplest fingerprint pattern
Examples on pg. 43: all show continuous flow up and out with no looping shoulder formation

2. Tented Arch (TA)

General: Still 0 deltas but some disturbance in center; three morphological variants but ALL coded simply “T” for Henry Classification.

a) Angular TA

Central ridge(s) form an angle $\le 90^{\circ}$
Looks like a small ^ or _/ shape in the middle

b) Up-thrust TA (most common)

One vertical ending ridge that shoots straight up in center (must actually be an ending ridge, not a bifurcation)
Angle may exceed $90^{\circ}$ , but ridge is upright

c) Loop-Type TA

Mimics a loop but fails one loop criterion (usually ridge count)
• Loop requirements recap: 1 delta, recurving core ridge, ridge count >1
• If apparent loop has ridge count $=1$ or 0 (delta touches core) → classify as TA-loop type
Often confused with loops; must inspect innermost recurving ridge & shoulders

Visual Practice

Pg. 44: Up-thrust TA example (students answered correctly in chat)
Pg. 46: Mixed TA gallery
• Some borderline prints could be argued loop vs. TA (real crime scenes rarely ideal)
• When uncertain, analysts compare to whole set—suspect with all arches may still match seemingly “loop-like” latent

Tempered-Card Marking

On card: a = plain arch, t = tented arch
(No need to write “angular,” “up-thrust,” etc.)

LOOP & ARCH ASSIGNMENT REMINDERS (Module 2)

Pattern-ID lab: 8 unknown prints
• Must specify subtype (ulnar/radial, whorl subtype, arch subtype)
• For loops state BOTH hands: “Left hand → ulnar, Right hand → radial” etc.
• Merely writing “left-slant” or “right-slant” is insufficient → points deducted
Personal thumb exercise: Ink or photograph your left thumb, report pattern, and EXPLAIN your reasoning (delta count, ridge count, flow, etc.)

WHORL REVIEW BEFORE TRACINGS

Four whorl subtypes: Plain, Central-Pocket, Double-Loop, Accidental
Each whorl already has ≥2 deltas → additional step: Whorl Tracing (replaces ridge count used for loops)

WHORL TRACING – Theory (Pg. 30–33)

Always start at left delta, drop to next lower continuous ridge, trace L → R until horizontally aligned with right delta
Depending on how many intervening ridges separate the tracing line from the right delta, mark as:
• Inner (I): inside the right delta, $\ge 3$ intervening ridges
• Meet (M): tracing ridge meets / aligns within $\le 2$ ridges of the right delta
• Outer (O): outside the right delta, $\ge 3$ intervening ridges

Mathematically:
\text{Count} = #\,(\text{distinct ridges between tracing line and right delta})
If $\text{Count} \ge 3$ and tracing lies inside → I
If $\text{Count} \le 2$ → M
If $\text{Count} \ge 3$ and tracing lies outside → O

Additional rules

Do NOT count tracing line or delta ridge itself
If tracing ridge bifurcates, continue on the lower branch ("take the low road")
If tracing ridge ends, drop vertically to next lower ridge and continue

WHORL TRACING – Worked Examples

Example drawing (inner)
- Deltas marked; tracing ends inside right delta with 5 intervening ridges → I
Example drawing (meet)
- Tracing aligns with right delta; only 1 ridge in between → M
Example drawing (outer)
- Tracing ends outside right delta; 3+ ridges (e.g., 4) between → O

Real-Print Walk-Throughs (Document Camera)

Double-Loop sample: deltas located; multiple drops required; 10+ ridges inside → I
Plain whorl sample: 5 ridges outside → O
Another whorl: tracing aligns after one ridge → M

Entering Tracings on Tempered Cards

Lower-right corner of each whorl finger box: write I, M, or O
• Example (Pg. 47) Right Thumb → PW/O (Plain Whorl, Outer)
Students should now finish remaining tracings on Pg. 47:
• Top card: fingers 4 & 9
• Bottom card: fingers 2 & 8

Connection to Henry Classification (Post-Midterm)

Loops contribute “ridge count” numerator/denominator values
Whorls contribute “tracing” letters I/M/O to Henry’s primary, secondary, and major groupings
Arches add no numerical value (simply placeholders “A” or “T”)
Mastery now ensures smoother progress when Henry fraction assignments begin

Ethical & Practical Notes

Latent crime-scene prints rarely exhibit textbook clarity; analysts must weigh ambiguous cases, compare entire ten-print sets, and document rationale
Proper notation crucial: inconsistent or missing loop hand-orientation will mislead automated AFIS searches and courtroom testimony

Immediate Action Items

Finish ARCHES/TENTED practice; mark Pg. 47 cards with a/t where needed
Complete WHORL TRACINGS for all whorls on Pg. 47, label I/M/O
Submit Module 2 deliverables by Sunday (biology & fetal dev + Pattern ID lab + personal left-thumb description)
Review pages 30–33, 40–47 before midterm; prioritize delta recognition, ridge counting, and tracing mechanics