# Rectilinear Locomotion in a Snake (Boa occidentalis)

> How does a heavy snake creep forward in a dead straight line? In a 1950 study, H. W. Lissmann filmed and X-rayed young boas and found that waves of muscle run backwards along the belly, so the belly moves in small steps while the backbone glides along steadily. The ribs do not “walk” at all: the snake moves much like an earthworm, a way of moving the author thought unique among vertebrates.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1950-lissmann-rectilinear-locomotion-snake-boa/

## Citation and access

- **Authors:** H. W. Lissmann
- **Year published:** 1950
- **Journal or source:** Journal of Experimental Biology
- **Full citation:** Lissmann, H. W. 1950. Rectilinear locomotion in a snake (Boa occidentalis). Journal of Experimental Biology 26(4): 368-379.
- **DOI:** 10.1242/jeb.26.4.368
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/1950_Lissmann_rectilinear-locomotion-in-a-snake.pdf

## Tags

- **Species:** Reptiles > Argentine boa
- **Region:** Europe > United Kingdom
- **Behaviour and ecology:** Behaviour; Movement
- **Methods and technology:** Direct observation
- **Data type:** Modelling or theoretical; New field data
- **Observer qualification:** Not needed
- **Discipline:** Behaviour and ecology
- **Year published:** 1950

## Detailed keywords

- **Species:** Studied: Boa occidentalis (named in the paper by its scientific name only; no common name given), two young snakes 57 cm and 60 cm long, lent by the Zoological Society of London. Other animals discussed for comparison: earthworms, snails and caterpillars. Other snake groups in which rectilinear movement had been described: Boidae (boas), Viperidae (vipers) and Ophisaurus.
- **Location and habitat:** Laboratory study at the Zoological Department, University of Cambridge (England). Snakes filmed creeping over a glass plate and through glass tubes. No field site.
- **Topics:** snake locomotion; rectilinear (straight-line) movement; comparison with serpentine, concertina and side-winding movement; waves of muscular contraction travelling from head to tail; stepwise movement of the belly versus steady movement of the backbone; role of the ribs (the “rib-walking theory” rejected); ventral skin muscles and the two sets of muscles linking ribs to belly skin (M. costo-cutanei superiores and inferiores); friction and anchoring of belly scales on the ground; comparison with earthworm, snail and caterpillar movement; use of rectilinear movement when approaching live prey.
- **Statistics or models:** No statistics. Measurements taken from film frames, force recordings and X-ray photographs, and a diagrammatic mechanical model of how the muscles work through one cycle. The paper refers to a Fig. 7 printed in a separate folder (“Folder V”), which is not in this PDF.
- **Data type:** New laboratory observations and measurements (no dates given apart from the paper being received on 17 November 1949), plus a theoretical model of the muscle mechanics. The old library listed this paper as 1949 (the year it was received); the journal issue is dated February 1950.

## Synopsis

### 1. What they did

Snakes move in four main ways: serpentine (side-to-side waves), concertina, side-winding, and a less common “rectilinear” movement, in which the whole snake creeps forward in a straight line without bending sideways. Earlier authors disagreed about how rectilinear movement works: some compared it to a snail or a caterpillar, and one old idea held that snakes “walk” on their ribs.

Lissmann studied two young Boa occidentalis, 57 and 60 cm long, in the laboratory:

- Filming. The snakes crept over a glass plate with a tilted mirror underneath, so the side and the belly could be filmed at the same time. Natural markings, scales and white paint marks were used to follow individual points on the body.

- Measuring forces. A snake crept from a fixed glass tube into a second tube hung on steel springs. Levers magnified the movement of the springs, which was photographed to show the pulling and pushing forces the snake made.

- X-rays. Small lead disks were stuck on the side of the belly and along the back, and a series of X-ray photographs showed whether the ribs moved relative to the backbone.

- Mechanical reasoning. From these results and the layout of the muscles, he worked out how the belly skin muscles and the two sets of muscles linking the ribs to the belly skin might act through each cycle.

### 2. What they found

- The boas used rectilinear movement slowly, often when approaching live prey. It could also be triggered by putting the snake on a smooth surface.

- Waves of muscle contraction and relaxation ran backwards along the belly, from head towards tail. Usually two complete waves were on the body at once. Sometimes a wave faded out before reaching the tail, as in earthworms.

- Each point on the belly moved forward in “steps” of 2 to 3 cm. While a stretch of belly was fully contracted, it stayed still on the ground (and on a very smooth surface could slip backwards). It then slid forward, speeding up as it relaxed and slowing as the next contraction came.

- The back, and with it the backbone, moved forward at a fairly steady speed. The head also moved at a steady speed.

- The force recordings matched those of an earthworm: a pull while the anchored stretch of the body was in the movable tube, changing to a push once that stretch had passed into the fixed tube.

- The X-rays showed the tips of the ribs kept the same position relative to the backbone. The skin slid past the rib tips instead: the same stretch of skin covered six more ribs when stretched than when contracted.

- In the mechanical model, the belly skin muscle is the main power source. The muscles linking ribs to belly skin probably lengthen and shorten in a regular rhythm, passing force between the belly and the backbone. The muscles running forward from the ribs to the skin and those running backward probably work against each other and take turns.

### 3. What they concluded

- Rectilinear movement in this boa is basically like an earthworm’s. The terms “snail principle” and “caterpillar principle” used by other authors are not appropriate.

- The ribs do not “walk”; this agrees with three earlier authors and contradicts the rib-walking theory.

- The backbone and everything firmly attached to it can be pictured as a cylinder gliding at steady speed inside a tube of skin and belly muscle, which moves forward at varying speeds and grips the ground in patches.

- The author says it is hard to prove with these methods exactly which muscles supply the forward force.

- Rectilinear movement is probably a unique kind of vertebrate movement, because it does not use the skeleton as levers.

### 6. Other technologies, skills or innovations

- Simultaneous filming of the side and belly through a glass plate and tilted mirror.

- A pair of glass tubes, one fixed and one hung on springs, with magnifying levers to record pulling and pushing forces.

- Lead disks on the skin and along the back, tracked on a series of X-ray photographs.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- Snakes moving this way travel in a straight line without sideways waves, so their trail would be expected to be straight rather than wavy. The paper does not describe trails; this is our observation for trackers to test.

- The paper notes that on rough ground the free back edges of the belly scales help anchor the stationary stretches of the body. This may help explain why stepwise, patchy contact could show in a snake’s trail on suitable ground.

## Cite this summary

Lawrence, K. 2026. Summary of: Rectilinear Locomotion in a Snake (Boa occidentalis) (Lissmann, 1950). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1950-lissmann-rectilinear-locomotion-snake-boa/