A Theory for the Function of the Spermaceti Organ of the Sperm Whale (Physeter Catodon L.)

A Theory for the Function of the Spermaceti Organ of the Sperm Whale (Physeter Catodon L.)

A Theory for the Function of the Spermaceti Organ of the Sperm Whale (Physeter catodon L.) KENNETH S. NORRIS Oceanic Znstitute and University of California, Los Angeles GEORGE W. HARVEY Oceanic Znstitute ITHIN THE SPERM WHALE FOREHEAD make diving possible by firmly closing the wlies the spermaceti organ, occupying outer and inner nasal passages.” They go on as much as 40 percent of the entire length of to 3ay : the whale. It is a huge, somewhat flattened, cone-shaped structure. It is covered dorsally We infer that its main function is to act as a force pump for the bony narial passages, and laterally by a thick wall of intermeshing drawing a great quantity of air into the ligamentous cables, many as thick as a man’s respiratory sacs and perhaps preventing the escape of air under the pressures of the great thumb. In the day of the hand whaler, this depths. It may also act in part as a hydro- stout outer structure was called “the case.” static organ since by severe contractions of part of its muscular sheath, the contained oil The organ is filled in life with as much as might be squeezed toward one end or the 1900 liters of a liquid, or semiliquid waxy oil, other, while the air sacs were being inflated, thus lightening the specific gravity of that the spermaceti-the material once so prized end and tending to alter the direction of for candles and illuminating oil. Surrounding motion of the animal. this organ at either end and below are air sacs, which are part of a complicated series of It is difficult to interpret exactly what highly asymmetrical nasal passages, valves, Raven and Gregory mean by a “force and associated structures. The functions of pump,” but we assume it means that move- this complex have been subject to some spec- ments of the spermaceti organ are capable of ulation. See discussion in Appendix. Also, drawing air out of the posterior air spaces Raven and Gregory (ref. 1) speculated that (lungs, trachea, head canals, middle ear) the case and its contained spermaceti “is to into the nasal sacs of the forehead. The idea, 397 398 ANIMAL ORIENTATION AND NAVIGATION FIGURE la. Sperm whale skeleton at the Museum of Comparative Zoology, Harvard University. Note the low channel-shaped rostrum and the amphi- theatrelike forehead. The spermaceti organ lies above the mtrum and is bounded posteriorly by the frontal sac which tightly adheres to the am- phitheatre walk. Photo courtay William Schevill, Haward University. we assume, is that such' additional air in the nasal sacs of the head when under pressure would serve to close the nasal passages enough to prevent air loss under the pressure of diving. The ideas are certainly partly in- correct for reasons we will discuss later, and the suggested functions seem unliiely. How- ever, we do not discount the possibility that the musculature of the forehead may be in- volved in a cycling of air within the sac sys- tem of the forehead. This paper presents a new theory for the function of the complex as a whole and brings forth some supportive evidence for our views. Briefly we suggest that ( 1) the sperma- FIGURE lb. Plan view of the sperm whale skull ceti organ is an acoustic resonating and showing the asymmetry of the superior bony nares sound-focussing chamber used to form and and their disparate sizes-from skull in La Angela County Museum. process burst-pulsed clicks; (2) the nasal pas- sages of the forehead not only allow the re- peated recycling of air for phonation during useful for long-range echolocation in the dives, but provide mirrors for sound reflec- deep sea. tion and processing; and (3) this entire sys- To show the basis for these ideas, we will tem allows sound signal production especially first examine the pertinent details of anat- SESSION V: SENSORY MECHANISMS-MECHANICAL 399 omy, then review what is known about the wholly ventral, like that of a shark, and the sounds of sperm whales, presenting at this rostrum lies above it, the great majority of time some new data, and then draw these the huge forehead of the whale is composed facts together into a coherent theory. Finally of soft tissue. we will describe a model of the sperm whale The bony nares pierce the rostrum near acoustic system with which we have pro- its base and are highly asymmetrical. At the duced simulated sperm whale signals. This surface of the rostrum in adult whales, the simple apparatus, which was built using engi- right naris is approximately one-seventh the neering design criteria we see in the animal, cross-sectional area of the left naris and is produces remarkably similar signals to those located on the midline lying almost equidist- recorded from living whales. ance from all points on the curved amphi- During the course of this work, two fetal theatre (fig. 1B). This amphitheatre is sperm whales were examined, an adult was formed largely by the premaxillary, maxillary dissected, and various samples obtained for and nasal bones. The larger left naris is well histologic analysis. The species was observed displaced to the left. and recorded at sea on three occasions. Var- In the living animal, the bony amphi- ious observations and measurements have theatre is covered over most of its area with been made on museum skeletal material. the tightly adhering posterior wall of the These ideas were conceived nearly 4 years frontal sac, a diverticulum of the right nasal ago and opportunity to test them has been passage. The bony rostrum, which in coronal sought since that time. It has not come easily, section is shallowly dish-shaped (fig. lA), is so the inforniation is presented at this time, filled by the “junk.” Junk is an old whaler’s incomplete as it is, in hope that others may term for this fatty mass, tightly bound in be able to contribute. connective tissue, that was less valuable than The ultimate proof, rejection, or refine- the spermaceti. It is separated from the sper- ment of our ideas must probably await exper- maceti organ above by a broad channel- iments on living sperm whales, but we feel shaped anterior branch of the right nasal pas- that our information is sufficiently advanced sage. and documented to make it useful at this time, especially in view of the rarity of op- Spermaceti Organ and Nasal Passages portunity to work on living examples of this The spermaceti organ extends posteriorly species. from just beneath the tip of the snout to the anterior skull amphitheatre. The great rela- THE ANATOMY OF THE SPERM WHALE FOREHEAD tive length of the organ is accounted for in part because the snout of adult sperm whales The Skull overhangs the upper jaw by about 5 percent of the total length in adults (ref. 2). The Perhaps the most noteworthy aspect of spermaceti organ is bounded at both ends by the sperm whale skull is the amphitheatre- the large vertically oriented air sacs men- like, nearly parabolic forehead and the broad tioned above. The ligamentous case sur- low rostrum extending forward from its base rounding the spermaceti organ is extremely to the tip of the snout (fig. lA, 1B). Because stout and difficult to pierce even with a sharp the slim elongated tooth-bearing lower jaw is knife. When one does penetrate this layer 4.0 ANIMAL ORIENTATION AND NAVIGATION sue, the distal sac is encountered, which spreads across the width of the snout. By re- flecting the walls of this sac, the museau du singe, or monkey’s muzzle (fig. 2A), is ex- posed (see refs. 3 and 4). This structure con- sists of a pair of extremely stout black lips, occupying nearly the entire width of the pos- terior wall of the distal sac (fig. 2B). They close the anterior end of the right nasal pas- sage. The spermaceti organ ends anteriorly In the upper lip of the rnuseau du singe as a very flattened oval of liquid-filled space that gives way anteriorly to more tightly bound FIGURE 2a. Museuu du Singe, or monkey’s muz- lipid material and finally to dense connective zle, of an 11-m sperm whale dissected at Rich- mond Whaling Station, California. Whale has tissue within the upper lip. The organ be- been cut throne the anterior snout at the point comes much deeper as one explores poster- of inflexion above the upper jaw and the distal iorly, in the form of a wedge, curving slightly sac reflected from the museau lips. In lower left over the junk until it reaches the amphi- comer note triangular band that normally rests theatre of the skull. There its posterior wall between the lips of the museau. Bulbous upper lip of the museau is actually the anterior exten. consists of a smooth, nearly circular, verti- sion of the spermaceti organ, and the lips cross its cally oriented wall that forms the smooth an- entire width. Rule in inches. terior face of the frontal sac. This wall looks very much like the head of a bass drum, although it is much more flaccid, and one during dissection of a fresh specimen, liquid may press it inward with a modest pressure, spermaceti exudes forth as if under consider- of the thumb. able pressure. To describe the organ in more detail, it seem best to start from the anterior end of the animal and work posteriorward to the amphitheatre of the skull. The anterior sur- face of the sperm whale snout is strongly in- dented both laterally and transversely across the whale’s forehead a few inches above the upper jaw, and flares out above into the bul- bous forehead which bears the asymmetri- cally placed single S-shaped blow hole on its anterolateral surface.

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