QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online August 31, 2004
Journal of Experimental Biology 207, 3483-3494 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01170

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Young, B. A. Articles by Singer, M. Search for Related Content PubMed PubMed Citation Articles by Young, B. A. Articles by Singer, M.

The buccal buckle: the functional morphology of venom spitting in cobras

Bruce A. Young^*, Karen Dunlap, Kristen Koenig and Meredith Singer

Department of Biology, Lafayette College, Easton, PA 18042, USA

View larger version (95K): [in a new window]   Fig. 1. Scanning electron micrographs of the exit orifice of a non-spitting cobra Naja kaouthia (left) and a spitting cobra Naja pallida (right). Note the differences in the shape of the exit orifice.

View larger version (96K): [in a new window]   Fig. 2. Deformations of the palato-maxillary arch during spitting. (A) Naja nigricollis immediately prior to spitting; note the deformation of the supralabial scales (arrow) caused by the frontal rotation of the maxilla; (B) a high-speed digital videograph recording of N. nigricollis spitting; note the ventral projections on the roof of the mouth (arrow). F, fang.

View larger version (60K): [in a new window]   Fig. 3. Illustration of the lateral view of the skull, and ventral view of the palato-maxillary arch, of Naja nigricollis. Muscle attachment sites are shown as solid colors (lateral surface) or broken colors (medial surface) for the following muscles: M. adductor mandibular externus superficialis (yellow); M. levator pterygoideus (purple); M. protractor pterygoideus (red); M. retractor pterygoideus (blue); M. pterygoideus (green). e, ectopterygoid; m, maxilla; pa, palatine; pf, prefrontal; pt, pterygoid.

View larger version (59K): [in a new window]   Fig. 4. Histology of the distal venom delivery system. (A) Frontal section of a spitting cobra Naja sputatrix showing the soft tissue chambers within the fang sheath. (B) Parasagittal section through N. sputatrix showing the venom duct approaching the lateral margin of the fang sheath. (C) Transverse section through the fang sheath of a non-spitting cobra N. melanoleuca illustrating the links between the fang sheath and the maxilla and the internal partitions of the fang sheath. c, venom chamber; d, venom duct; f, fang; m, maxilla; pa, palatine; s, fang sheath; v, venom vestibule.

View larger version (123K): [in a new window]   Fig. 5. Ventral view of the palate of an Indochinese spitting cobra Naja siamensis before (A) and after (B) stimulation of the M. protractor pterygoideus. Both A and B are photos of the same side of the same animal; B was transposed to enhance comparison. Note the protraction and rotations of the palato-maxillary arch. f, fang; pa, palatine; pt, pterygoid.

View larger version (17K): [in a new window]   Fig. 6. Data tracings from two separate experiments in which strain gauges were placed on the palatal mucosa (A) or scales over the nasofrontal joint (B) of two separate spitting cobras Naja nigricollis. In both experiments contraction of the M. protractor pterygoideus, either artificially (A) or during spitting (B), resulted in deformations of the palato-maxillary arch evident in the strain gauge tracings.

View larger version (27K): [in a new window]   Fig. 7. Data tracings of venom pressure recorded from the fang tip of Naja nigricollis. Note that stimulation of the M. adductor mandibulae externus superficialis (AMES) simultaneously with the M. protractor pterygoideus (PP) produces greater venom pressure than when either is stimulated alone. This pattern holds whether the muscles are given twitch (A) or train (B) stimuli.

View larger version (13K): [in a new window]   Fig. 8. Data tracings of venom pressure recorded from the venom duct of Naja nigricollis. Note that stimulation of the M. protractor pterygoideus (PP) had minimal influence on venom pressure, and there was no additive effect when stimulated simultaneously with the M. adductor mandibulae externus superficialis (AMES). Note the marked increase in venom pressures recorded at the venom duct compared to those recorded from the fang tip (Fig. 7).

View larger version (18K): [in a new window]   Fig. 9. Representative EMG tracing recorded when Naja nigricollis spat venom. Note the temporal congruence in the activity patterns of the M. adductor mandibulae externus superficialis (AMES) and the M. protractor pterygoideus (PP). Because the venom must travel from the fang to the detector, the signal from the spit detector is always delayed relative to the electrical activity within the muscles.

View larger version (42K): [in a new window]   Fig. 10. Summary model for the mechanics of venom spitting. The palato-maxillary arch (comprising the pterygoid, palatine, ectopterygoid and maxilla) articulates with the skull at the prefrontal (black rectangle). Immediately adjacent to the palato-maxillary arch is the venom gland and duct; the fang sheath covers the anterior portion of the maxilla and venom duct. The system at rest is shown from a lateral (A) and dorsal (B) perspective. Upon contraction of the M. protractor pterygoideus (PP) the palato-maxillary arch is protracted, rotated in the sagittal plane (C), and rotated in the frontal plane (D). These rotations displace the fang sheath (D,E), removing barriers to venom flow such that when the M. adductor mandibulae externus superficialis (AMES) contracts, venom pressure can expel venom through the specialized exit orifice of the fang (E). P, pressure; F, fang.

View larger version (10K): [in a new window]   Fig. 11. Three hypotheses for the temporal pattern in the activation of the M. adductor mandibulae externus superficialis (AMES) and M. protractor pterygoideus (PP). (A) The AMES maintains a prolonged contraction resulting in sustained venom pressure (VP) within the venom gland; under this hypothesis the kinematics of the spit (SK) would be characterized by marked increases and decreases in venom flow. (B) Temporally congruent patterns in the AMES and PP, leading to congruent bell-shaped curves for venom pressure and spit kinematics. (C) Prolonged contraction of the PP with intermittent contract of the AMES, leading to variable patterns of venom pressure and spit kinematics.