A Morphological and 13C NMR Study ofthe Extramandibular Fat Bodies of theStriped Dolphin (Stenella coeruleoalba)

C. MAXIA,1 P. SCANO,2 F. MAGGIANI,3 D. MURTAS,1 F. PIRAS,1

R. CRNJAR,3 A. LAI,3 AND P. SIRIGU2*1Department of Cytomorphology, University of Cagliari, Italy

2Department of Chemical Sciences, University of Cagliari, Italy3Department of Experimental Biology, University of Cagliari, Italy

ABSTRACTThe molecular and histological structure of the fat bodies covering

externally the posterolateral region of the jaw of the striped dolphin(Stenella coeruleoalba) was investigated by means of morphological andnuclear magnetic resonance techniques. The analyses of samples belong-ing to adult and juvenile individuals were performed with the aim ofseeking the presence of age-related differences. In our study, the level ofisovalerate (iso5:0) in the extramandibular fat of the juvenile individualsis comparable with those of the adult counterparts; conversely, longer iso-branched fatty acids were detected in lower quantities in the juveniles to-gether with a higher degree of unsaturation. The morphologic analysesrevealed that, in both adults and juveniles, this fatty tissue is similar tounivacuolar adipose tissue. However, in the juveniles, a muscular compo-nent was present, whereas only in adult subjects, enlarged and irregu-larly shaped cavities may be seen within the adipose tissue. Thesecavities, structurally organized as veins, may regulate blood flow inresponse to changing water temperature and stabilize thermal gradientwithin the jaw lipids. These data suggest that the molecular compo-nents and the histological organization can indicate a maturation of theorgan with age that probably may reflect different sound reception proper-ties. Anat Rec, 290:913–919, 2007. � 2007Wiley-Liss, Inc.

Key words: extramandibular fat; striped dolphin; NMR; mor-phology; lipids

Several marine mammals have evolved an echolocat-ing system called biosonar. In particular, odontocetesecholocate by producing clicking sounds and receivingand interpreting the resulting echo. By means of thissystem, toothed whales and dolphins can identify objectsand animals out of their sighting range, thus obtaininginformation on their size, number, shape, texture, andspeed (Kuc, 1996; Hoffmann et al., 1998; Au, 2002).

The organs devoted to the production and propagationof the sound are the ‘‘monkey lips’’/dorsal bursa (MLDBcomplex) and the melon, respectively. The echoed soundsare received and conducted through the lower jaw to themiddle ear, inner ear, and then to hearing centers in thebrain by means of the auditory nerve. The brain receivesthe sound waves in the form of nerve impulses, whichrelay the messages of sound and enable the dolphin to

Abbreviations used: iso5:0 ¼ isovaleric acid; NMR ¼ NuclearMagnetic Resonance; TAG ¼ triacylglycerols; WE ¼ wax esters;mol% ¼ molar; MUFA ¼ mono unsaturated fatty acids; PUFA ¼poly unsaturated fatty acids; 2-MBA ¼ 2-Methylbutyric acid;IBA ¼ Isobutyric acid.

*Correspondence to: Paola Sirigu, Department of Cytomor-phology, University of Cagliari, Cittadella Universitaria di Mon-serrato, S.S. 554 – Bivio per Sestu, 09042 Monserrato (CA),Italy. Fax: 39-070-675-4003. E-mail: psirigu@unica.it

Received 5 April 2005; Accepted 11 April 2007

DOI 10.1002/ar.20560Published online 21 May 2007 in Wiley InterScience (www.interscience.wiley.com).

� 2007 WILEY-LISS, INC.

Imaging Fat THE ANATOMICAL RECORD 290:913–919 (2007)

interpret the sound’s meaning (Au, 2002). Age-relatedstructural and compositional differences were reportedfor the melon of several odontocete species, thus suggest-ing that echolocation undergoes a maturation processthrough aging (Koopman et al., 2003; Scano et al., 2005).Whereas the role of the melon in transmitting the

sounds produced in the nasal sac to the water is clear,the contribution of the lower jaw in echolocation hasbeen only supposed. The lower jaw construct of the dol-phin consists of two mandibular bones (fused in onemandible), and the teeth. The mandible is hollow andthin, with a particular flared area, known as the ‘‘panbone,’’ existing at the posterolateral third of the jaw(Wartzok and Ketten, 1999). The lower jawbone cavity isfilled with fat bodies, rich in isovaleric acid. Externally,the pan bone region of each side of the lower jaw is cov-ered with a fat deposit; it apparently continues with thelipids of the melon and of the channel inside the jaw,and extends toward the throat and from the posterior ofthe jaw to make contact with the tympano-periotic com-plex (Norris, 1968; Varanasi and Malins, 1970, 1971;Morris, 1986). This fat acts as a low density sound chan-nel and conducts sounds from the flared portion of thelower jaw directly to the middle ear (Berta and Sumich,1999).Several studies report that the molecular composition

of the mandibular fat is similar to that of the melon, butdiffers from blubber fat, and it is instrumental in soundtransmission (Litchfield and Greenberg, 1974; Litchfieldet al., 1975). It is worth noting that several studiesreported that metabolism in this tissue is nominal(Cranford et al., 1996; Koopman et al., 2003; Houseret al., 2004). Some authors (Ames et al., 2002; Scanoet al., 2005) report that this acoustic tissue contains fewdietary lipids but high concentrations of endogenouslysynthesized branched iso-acids, among which isovalerate(iso5:0) is the most abundant molecular component. Thepresence of wax esters was also detected.In a previous study (Scano et al., 2005), the melon of

the striped dolphin (Stenella coeruleoalba), a speciesabout which scanty information is available, was investi-gated by morphological and high-resolution 13C nuclearmagnetic resonance (NMR) methods, the latter being themost suitable and nondestructive technique to analyzethe lipid components in a complex mixture of compounds(Jie and Mustafa, 1997; Halliday et al., 1998). We char-acterized structure and composition at the histologicaland molecular level of two different regions (referred toas basal and apical) of the melon of both adult and juve-nile individuals. The aim of the present work is toextend our above-mentioned study, by the same techni-ques, to the investigation of the molecular and histologi-cal structure of the fat bodies covering the pan bone oflower jaw of the striped dolphin. The analyses ofsamples belonging to adult and juvenile individualswere performed with the aim of seeking age-relateddifferences.

MATERIALS AND METHODS

We examined samples of extramandibular fat of thelower posterior jaw (Fig. 1) belonging to five individualsof Stenella coeruleoalba, here designated as adult 1 (age,12–13 yr; sex, M), adult 2 (age, 15–17 yr; sex, F), adult 3(age, 30–32 yr; sex, M), juvenile 1 (age, 3–5 months; sex,

M), and juvenile 2 (age, 6–8 months; sex, F). The age ofthe dolphins was determined by counting dentine layersin sections of the teeth (Ridgway et al., 1975).All tissue samples were dissected from dolphins found

stranded along the shore of Sardinia (Italy) and theMediterranean coasts of France in 2003 and 2004. Sam-ples were from animals of approximately 2–12 hr post-mortem time, and the data described in this study wereobtained only from fresh or good-quality specimens. Theheads were removed from the rest of the body, trans-ferred to the Department of Experimental Biology, andcompletely dissected at the Department of Cytomorphol-ogy. After the complete excision of the extramandibularfat bodies, multiple fat samples were obtained from alldifferent regions. Each sample was divided in two parts:the former was reduced in 1 3 5 cm logs, introduced inNMR tubes and immediately analyzed; the latter, cut inspecimens of 2 3 1 cm for the morphological examina-tion, was fixed in 10% buffered formalin for 24 hr andprocessed for paraffin embedding.

Morphology

Because of the peculiar structure and composition ofthe tissues examined, we encountered difficulties inobtaining cryostat sections, because the tissue sampleswere not hard enough for cutting at �358C. Thus, thestudy was carried out on formalin-fixed and paraffin-embedded microtome sections. Nevertheless, the histo-logical treatment adopted for the paraffin-embeddingtechnique, which consisted of dehydration in ethyl alco-hol and diaphanation in xylene before inclusion, causedthe solubilization of the lipids present in the tissues.Finally, the sections (6–7 mm) were stained with hema-toxylin–eosin. Adjacent sections were used for the histo-chemical Masson’s trichromic staining modified by Gold-ner for the elastic fibers, connective tissue, and collagen.The histological features were evaluated by light mi-

croscopy using a Zeiss microscope (AxioPhot2, Carl ZeissVision GmbH, Hallbergmoos, Germany); images wereacquired and processed by graphic card Matrox MeteorPCI Frame Grabber (Matrox Electronics Systems Ltd.,Dorval, Canada) and by Zeiss AxioVision Software Rel.3.0 (Carl Zeiss Vision GmbH), respectively.

NMR Spectroscopy

Intact portions of tissue were examined in nonrotating10-mm NMR tubes, without solvent, at 258C. The 13Cspectra were run on a Varian VXR-300 spectrometer atoperating frequencies of 75.4 MHz. The 13C spectra wereacquired using the NOE-suppressed, inverse-gated,proton decoupled technique (Waltz-16), with 1 sec of ac-quisition time, using a sweep width of 13 KHz. Onethousand scans were collected using a 90-degree excita-tion pulse and a delay of 30 sec to allow for completerelaxation of each 13C signal.

RESULTSMorphology

Morphological analysis of the external fat of the pos-terolateral jaw showed that the lipid component isorganized in an adipose tissue, with voluminous rounded

914 MAXIA ET AL.

cells (Fig. 2). In both adults and juveniles, this adiposetissue is morphologically similar to univacuolar adiposetissue composed of closely related cells, with the nucleus

localized marginally between the plasma membrane anda big cytoplasmic lipid drop, and little extracellular ma-trix. Structural differences related to age were noticed:while in the juveniles a muscular component wasobserved, with bundles of fibers inserted in the adiposemass (Fig. 2d), not muscle fibers were found in thecorresponding tissue of adults (Fig. 2a–c). The adiposetissue of adults presented instead large and irregularlyshaped cavities (Fig. 2a–c). These cavities were gener-ally empty or sometimes contained few blood cells. Thecavities were bordered by a thin wall of flat cells, lyingabove a consistent layer of connective tissue, and werestructurally organized as veins (Fig. 2a–c).

NMR

The 13C NMR spectra of intact tissues of the fat bodiesof the lower posterior jaw of adults and juveniles ofStenella (Fig. 3) showed patterns of signals characteris-tic of lipid components, whereas no signal was observedfor the molecular components of the muscular tissues.This result can be ascribed to the fact that the molecularcomponents occurring in the muscles present so slowmolecular motion that the related NMR signals arebroadened beyond detection. The assignment of the sig-nals, reported in Table 1, was obtained according to datareported in a previous study of the melon of Stenellaand references cited therein (Scano et al., 2005).In all of the examined samples, triacylglycerols (TAG)

and wax esters (WE), composed of linear, isovaleric, andlonger isobranched fatty acids, were observed. In partic-

Fig. 1. Anatomical dissection of the extramandibular fat bodies ofStenella coeruleoalba.

Fig. 2. Morphological analysis of the fat bodies of the posterolat-eral jaw of Stenella coeruleoalba. a–c: Adult. d: Juvenile. In bothadults and juveniles, the adipose tissue is morphologically similar tounivacuolar adipose tissue composed of closely related cells and littleextracellular matrix. d: In the juveniles, a muscular component, withbundles of fibers inserted in the adipose mass, is present. a–c: In

adults, enlarged and irregularly shaped cavities are seen within theadipose mass. These cavities, generally empty, are structurally organ-ized as veins. In b, an enlarged detail of a, the different histologicalstructure between veins and arteries is shown. Masson’s trichromicstaining modified by Goldner. Original magnification ¼ 340 in a, 3100in b–d.

915HISTOLOGICAL AND NMR STUDY OF STENELLA JAW

ular, the presence of 2-methylbutyric and isobutyricacids was detected in the NMR spectrum of the calves ofStenella. In the latter samples, the NMR spectrumshowed signals at 182.68 and 20.03 ppm attributed tothe muscle metabolite lactate. Furthermore, the peak at54.66 ppm can be attributed to the -Nþ(CH3)3- functionalgroup of phosphatidylcholine and/or to the -CH2- groupof creatine/phosphocreatine.The quantitative analysis was performed measuring

the integrated areas of the 13C NMR signals; the data(mol %) are reported in Table 2. As far as the major lipidcomponents (TAG and WE) are concerned, differentresults were found comparing the data concerning thejaw fat bodies of the adult individuals. In all of theinvestigated samples the concentration of the isovaleratecompound was calculated as more than 50% of the totalfatty acids. Smaller quantities of linear fatty acids and alower degree of unsaturation were estimated in theadults as compared with the juveniles samples. More-over, no topographical variations in the lipid compositionof the extramandibular fat bodies of adults and juveniledolphins was found.

DISCUSSION

Au (1997) defines echolocation in dolphins as ‘‘the pro-cess whereby sounds are emitted and returning echoesare analyzed to detect and recognize objects under-water.’’ By echolocation, the presence of objects, theirsize, structure, material composition, and shape can bedetermined. It is widely accepted that the lower jaw actsas a specialized receiver that picks up and conducts the

echoes bouncing back from the environments to theauditory bullae (Au, 1993). The lower jaw of the dolphinis hollow with a particularly thin area, known as the‘‘pan,’’ located in the posterolateral region of the jaw.The mandibular canals are filled with fatty deposits,

rich in isovaleric acid, which extend from the posteriorjaw to make contact with the tympano-periotic complex(Varanasi and Malins, 1970, 1971). This fat is an excel-lent sound conductor as it presents a low impedancewith respect to water (Au, 1993). Sound energy travelingthrough water causes vibrations in the region of thelower jaw due to the thinness of the bone (Hughes,1999). Once within the jaw, the sound waves can betransmitted to the bulla and subsequently toward thecochlea by the acoustic fat surrounding this area.In Tursiops truncatus after the intravenous adminis-

tration of 99mTc-bicisate followed by scanning with singlephoton emission computed tomography, Houser and col-leagues (2004) detected a significant uptake of the ligandin the posterior region of the lower jaw indicative ofperfusion to the fat bodies of this tissue. They suggestthat such blood flow functions as a thermoregulatorycontrol of lipid density in the lower jaw, as the soundvelocity is inversely related to the temperature of acous-tic lipids. This finding agrees with our finding, inStenella coeruleoalba, of wide and enlarged veins thatspread throughout the extramandibular fat. These ves-sels may regulate the blood flow in response to changingwater temperature and stabilize thermal gradientswithin the lipids of the jaw by varying heat availabilityto this region. Houser et al. (2004) also reported a sub-stantial 99mTc-bicisate uptake in the melon, although inour previous study (Scano et al., 2005), we did not find

Fig. 3. 13C nuclear magnetic resonance spectrum of intact tissue of juvenile posterolateral jaw ofStenella coeruleoalba, assignments of the numbered resonances are reported in Table 1. ppm, parts permillion.

916 MAXIA ET AL.

TABLE 1. Peak assignments for 13C nuclear magnetic resonance spectrum of intact tissueof jaw fat bodies of a juvenile of Stenella

Peak Compound Carbon (ppm)a

1 Lactate -COO-CH- 182.692 2-MBA, IBAb -COO-CH- 176.21, 175.573 All fatty acids except 2-MBA, IBA -COO-CH2- 172.02, 171.674 External olefinic (MUFA and PUFAc) -CH¼CH-CH2-CH¼CH--CH2-CH¼CH- CH2- 130.175 Internal olefinic (PUFA) -CH¼CH-CH2-CH¼CH- 128.466 Glycerol backbone TAG -CH-O-CO- 69.577 Fatty alcohols in waxes -CH2-O-CO- 64.248 Glycerol backbone TAG -CH2-O-CO- 62.409 Phosphatidylcholine, Creatine, Phosphocreatine -Nþ(CH3)3 54.66

10 Isovaleric acid -COO-CH2-CH-(CH3)2 43.3011 2-MBA -COO-CH-(CH3)-CH2-CH3 41.2412 Isobranched fatty acids x3d 39.7313 All fatty acids except isovaleric -COO-CH2- 34.4013 IBA -COO-CH-(CH3)2 34.4014 Linear fatty acids x3 32.6115 All fatty acids -(CH2)n- 30.41, 30.0616 Isobranched fatty acids x2 x4 28.6117 Fatty alcohols in waxes -CH2-CH2-O-CO- 27.7817 Unsaturated fatty acids -CH2-CH¼CH-CH2- 27.7818 Fatty alcohols in waxes -CH2-CH2-CH2-O-CO- 26.6119 Isovaleric fatty acid -COO-CH2-CH-(CH3)2- 26.0120 All fatty acids -COO- CH2-CH2- 25.4420 Polyunsaturated fatty acids -CH¼CH-CH2-CH¼CH- 25.4421 Linear fatty acids x2 23.3222 Isobranched and isovaleric fatty acids -(CH3)2 22.7623 All n-3 fatty acids x2 21.0824 Lactate -CH3 20.0325 IBA -(CH3)2 19.3026 2-MBA -CH-(CH3)-CH2-CH3 16.9127 Linear fatty acids -CH3 14.5528 2-MBA -CH2-CH3 11.95

aChemical shift values are referenced to tetramethylsilane.b2-MBA, 2-methylbutyric acid; IBA, isobutyric acid.cMUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids.dCarbon number 3 from the methyl end.

TABLE 2. Percentage content (mol%) obtained by 13C nuclear magnetic resonance quantitativeanalysis of jaw fat of adults and juveniles of Stenella

Content (mol%)

Adult 1 Adult 2 Adult 3 Calf 1 Calf 2

Major lipid classesa

WE 47.43 27.00 38.42 28.91 26.85TAG 52.57 73.00 65.04 71.09 69.08

Saturated and unsaturated fatty acids and alcoholsb

Saturated 97.16 94.43 95.23 63.32 60.57MUFA 2.84 4.43 3.28 24.21 21.38PUFA 1.14 1.03 12.47 13.01

Typology of fatty acids and alcoholsc

Linear 11.15 11.31 11.23 37.34 37.15Isobranched 30.02 26.03 28.06 11.82 13.24Isovalericd 58.83 62.07 60.58 50.86 50.36

Chain length of fatty acids and alcoholse

Mean 14.09 12.86 13.42 11.77 11.51

Note. WE, wax esters; TAG, triacylglycerols.aCalculated from peaks 6 and 7.bThe MUFA (monounsaturated fatty acids) and the PUFA (polyunsaturated fatty acids) contents were measured from theratio of half area of peak 4 and 5, respectively, and area of the carboxyl signal which was normalized as 100, since peak 4comprises signals from the PUFA, the PUFA content was then subtracted from the MUFA content.cThe contents of isovaleric, isobranched and linear fatty acids, and alcohols were measured from areas of peaks 10, 12, 27,respectively.dPresents only as fatty acid.eThe chain length of fatty acids, except of iso5:0, was calculated as the ratio between the sum of the areas of all the ole-finic, methanetriyl methylene, and methyl functional groups (with the exclusion of the glycerol signals) and the acyl carbonatoms.

917HISTOLOGICAL AND NMR STUDY OF STENELLA JAW

any hints of blood vessels in melon of Stenella, similarto those detected in extramandibular fat. This finding isprobably due to the fact that we studied a sampleobtained from the central part of melon, whereas Houserand coauthors revealed the greatest uptake in its frontalportion.It is widely accepted that the echolocating organs

involved in sound propagation and reception of soundsundergo a maturation process through aging (Gardnerand Varanasi, 2003). In a previous study (Scano et al.,2005), we reported morphological and molecular differ-ences between the melon of the adult and that of thejuvenile of Stenella that may reflect different soundtransmission and conduction properties related to themelon maturation stage. Koopman et al. (2003) reportedthat the patterns of accumulation of iso5:0 in differenttissues (blubber, melon, and mandibular fats) of theharbor porpoises is age-related; isovalerate concentra-tions in melon increased from 12% to 35% in the firstyear of life, reaching a steady state by the age of 1 or2 years. In the present study in Stenella, the level ofiso5:0 (mol%) as calculated from the integrated areas ofthe 13C NMR spectrum of the fat bodies externallycovering the jaw in the juvenile is comparable to thoseof the adult counterparts: it cannot be, therefore,regarded as an index of maturity of the organ. Onthe other hand, a much lower degree of unsaturationtogether with higher amounts of isobranched fattyacids were detected in the adults; all of these compoundsare known to slow down sound transmission (Morris,1975).Age-related structural differences were also noticed

in the extramandibular fat: a muscular component, withbundles of fibers inserted in the adipose mass, wasobserved in the juvenile, but not in the adults. Thisfinding is confirmed by the presence in the 13C NMRquantitative spectrum of the samples of the juvenile ofsignals attributed to muscle metabolite lactate.The morphological analysis of the extramandibular fat

showed that, in both adults and juveniles, it is organizedas univacuolar adipose tissue, constituted of closely re-lated cells, with the nucleus localized marginallybetween the plasma membrane and a big cytoplasmiclipid drop, and little extracellular matrix; an analogoushistological organization was previously reported inthe adipose tissue of the melon of Stenella coeru-leoalba (Scano et al., 2005). Furthermore, we observedthat the adipose tissue of the juvenile lower jaw iscomposed of smaller cells than those of the adult coun-terparts. This finding was confirmed by the presencein the 13C NMR quantitative spectrum of the lowerjaw fat bodies of the juvenile of signals attributable tophospholipids, that compose the cellular membranes.These results confirm the hypothesis of Gardner andVaranasi (2003) on Phocoena phocoena and Tursiopstruncatus that the acoustic system is not fully devel-oped at birth and that its biochemical structurechanges throughout development.In summary, the innovative integration of NMR and

morphological techniques led us to demonstrate that thefat bodies of the posterolateral region of the jaw ofStenella coeruleoalba, as in the case of the melon, ismorphologically organized as peculiar adipose tissue, themolecular components of which are different from thoseof blubber. Taking into consideration the structural dif-

ferences between adult and juvenile, we can concludethat the molecular components and the histologicalorganization may indicate a maturation of the organwith age that probably reflect different sound receptionproperties.

ACKNOWLEDGMENTS

We thank the GECEM (Groupe d’Etude des Cetacesde Mediterranee) and the CSC (Centro Studi Cetacei,Italy) organizations for contributing and assisting withsample collection, and Mrs. Nicoletta Zinnarosu andMr. Massimo Annis for their expert technical assistance.

LITERATURE CITED

Ames AL, Van Vleet ES, Reynolds JE. 2002. Comparison of lipidsin selected tissues of the Florida manatee (Order Sirenia) andbottlenose dolphin (Order Cetacea: Suborder Odontoceti). CompBiochem Physiol 132:625–634.

Au WW. 1993. The sonar signal transmission system. In sonar ofdolphins. New York: Springer Verlag. p 77–97.

Au WW. 1997. Echolocation in dolphins with dolphin–bat compari-son. Bioacoustics 8:137–162.

Au WW. 2002. Odontocete echolocation. In: Perrin WF, Wursig B,Thewissen HGM, editors. Encyclopedia of marine mammals. SanDiego: Academic Press. p 358–367.

Berta A, Sumich JL. 1999. Sounds production for communication,echolocation, and prey capture. In: Berta A, Sumich JL, editors.Marine mammals evolutionary biology. San Diego: AcademicPress. p 255–289.

Cranford TW, Amundin M, Norris KS. 1996. Functional morphologyand homology in the odontocete nasal complex: implications forsound generation. J Morphol 228:223–285.

Gardner SC, Varanasi U. 2003. Isovaleric acid accumulation inodontocete melon during development. Naturwissenschaften 90:528–531.

Halliday KR, Fenoglio-Preiser C, Sillerud LO. 1998. Differentiationof human tumors from nonmalignant tissue by natural-abundance 13C NMR spectroscopy. Magn Reson Med 7:384–411.

Hoffmann M, Hermann LM, Pack AA. 1998. Seeing through sound:dolphins (Tursiops truncatus) perceive the spatial structure ofobjects through echolocation. J Comp Psychol 112:292–305.

Houser DS, Finneran J, Carder D, Van Bonn W, Smith C, Hoh C,Mattrey R, Ridgway S. 2004. Structural and functional imagingof bottlenose dolphin (Tursiops truncatus) cranial anatomy. J ExpBiol 207:3657–3665.

Hughes HC. 1999. The dolphin’s sonar receiver. In: Sensory exotica.Boston: The MIT Press. p 108–116.

Jie MS, Mustafa J. 1997. High-resolution nuclear magneticresonance spectroscopy-Applications to fatty acids and triacylgly-cerols. Lipids 32:1019–1034.

Kuc R. 1996. Biologically motivated adaptive sonar system.J Acoust Soc Am 100:1849–1854.

Koopman HN, Iverson SJ, Read AJ. 2003. High concentrations ofisovaleric acid in the fats of odontocetes: variation and patterns ofaccumulation in blubber vs. stability in the melon. J Comp Phys-iol B 173:247–261.

Litchfield C, Greenberg A.J. 1974. Comparative lipid patterns inthe melon fats of dolphins, porpoises and toothed whales. CompBiochem Physiol 47B:401–407.

Litchfield C, Greenberg AJ, Caldwell DK, Caldwell MC, Sipos JC,Ackman RG. 1975. Comparative lipid patterns in acoustical andno acoustical fatty tissues of dolphins, porpoises and toothedwhales. Comp Biochem Physiol 50B:591–597.

Morris RJ. 1975. Further studies into the lipid structure of thespermaceti organ of the sperm whale (Physter catodon). Deep-seaResearch 22:483–489.

918 MAXIA ET AL.

Morris R. 1986. The acoustic faculty of dolphins. In: Bryden MM, Har-rison R, editors. Research on dolphins. New York: Clarendon. p 369–399.

Norris KS. 1968. The evolution of acoustic mechanism in odontocetecetaceans. In: Drake ET, editor. Evolution and environment. NewHaven: Yale University Press. p 297–324.

Ridgway SH, Green RF, Sweeney JC. 1975. Mandibular anesthesiaand tooth extraction in the bottlenosed dolphin. J Wildl Dis 11:415–418.

Scano P, Maxia C, Maggiani F, Crnjar R, Lai A, Sirigu P. 2005.A histological and NMR study of the melon of the striped dolphin(Stenella coeruleoalba). Chem Phys Lipids 134:21–28.

Varanasi U, Malins DC. 1970. Unusual wax esters from the man-dibular canal of the porpoise (Tursiops gilli). Biochemistry 9:3629–3631.

Varanasi U, Malins DC. 1971. Unique lipids of the porpoise(Tursiops gilli): differences in triacyl glycerols and wax esters ofacoustic (mandibular canal and melon) and blubber tissues.Biochim Biophys Acta 231:415–418.

Wartzok D, Ketten DR. 1999. Marine mammals sensory systems.In: Reynolds JE III, Rommel SA, editors. Biology of marine mam-mals. Washington, DC: Smithsonian Institution Press. p 117–175.

919HISTOLOGICAL AND NMR STUDY OF STENELLA JAW