A dissection of the larynx of a humpback whale calf with a review of its functional morphology

3 Pages·1991·1.3 MB·

by  C J Quayle

A DISSECTION OFTHH LARYNX OF A HUMPBACK WHALECALF
WITH A REVIEW OF ITS FUNCTIONAL MORPHOLOGY
QUAYLE
C.J.
Quayle,C.J. 1^0} 07 1: Adissectionoi"the larynxofahumpbackwhalec;ilfwithareview
of its functional morphology, Memoirs of the Queensland Museum 30(2); 351 354.
Brisbane. ISSN 0079-8835.
The larynx ol a humpback whale Ctlf *M dissected. The anatomy conformed with the
general mammalian pattern with the addition ofa ventral diverticulum. Some LhOUghta as
to how the organ might function arc considered. \^} Humpback whale, larynx, unatomy,
function
CJ. Quayte, 7<J Wtekham 1errace. Unshtmv4000: 20December J990
A humpback wbalc calf (QM.IM7303) The larynx was a tubular organ with a car-
stranded at Moon Point, Frascr Island in Oc- tilaginous skeleton. There were three unpaired
tober, IMS1) was frozen soon after death and cartilages,theepiglottic, th\roitiand cricoid,and
delivered to the Queensland Museum, Brisbane. one pair of arytenoid cartilages. Caudally the
Il presented an almost unique opportunity to larynx became continuous with the trachea. The
examine a larynx of manageable size with min- tube was lined with what appeared to be
imal postmortem changes. The calf was 4.2 m squamousepithelium. Thiswastough andclose-
long and estimated to be about four weeks old. ly applied particularly over the arytenoid car-
The respiratory tract began with two tilages (compare human vocal cords). The
blowholes, slits about Scrtl long on each side of cartilageswerejoinedby musclesmostofwhich
the midlineand inclinedsothattheir rostral ends could be identified as following the general
were closest together. The blowholes were lined mammalian pattern.
with biack skin which continued to the base of The thyroid cartilage consisted oftwo alae or
the skull where it became continuous with the plates continuous in the ventral midline and
mucous membrane. widely deficient dorsally. There was a small
The blowholesweresurroundedby fibro-fatty rostral cornua and a long caudal one equivalent
tissue without obvious musculature. From their to the greater comua of the human thyroid car-
external entrance the blowholes ran almost tilage.The latter articulated with the cricoid car-
horizontally eaudally in bony grooves ending as tilage on each side. There was a Hat ovoid facet
the bony posteriorchoanac. Thevomerine bone contiguous on each cartilage and the joint had a
of the skull here separated the airway into two thick fibrous capsularmembrane.
channels, The air passage then became a single The cricoid cartilage was complete dorsullv
thin-walled tube which continued, inclined where it formed a large rectangular plate
ventrally. to meet the thick-walled muscular 18x12cm. It wasdeficientventrally (Fig 1). The
orophaiynx at an acute angle. This arrangement dorsal plate mergedwith the uppertrachealrings
suggestsavalve. This length oflube appeared to forming a substantial crico-tracheal plate.
be he equivalent ofthe human nasopharynx. Caudally and laterally wasthe facet forarticula-
i
The larynx itselfwas horizontally disposed. It tion with the greater cornu of the thyroid car-
pleasured 20cm from the tip of the epiglottis to tilage. On each rostral shoulder was a large
the first tracheal ring. Compared with its human synovial joint articulating with its respective
counterpart itwas in close proximity to the skull arytenoid cartilage. The lateral plates of the
base with the tip of the epiglottis extending al- cricoid were narrow rostrally and broadcaudal-
most to the posteriorchoana within the conduit, ly. Within the ventral deficiency lay the ventral
have called, the nasopharynx. In this respect diverticulum. A very thick band of muscle, lar-
I
elongation ofthe human pharynges is said to be gely transversally disposed (the thyroarytenoid
die result of a vertical stance. The food passage muscle) filled the space between the lateral alac
passed on each side of the laryngeal opening as and covered the diverticulum.
twopyriform fossaetobecome a single tube, the Each arytenoid was complex in shape ar-
oesophagus, dorsal to the trachea. ticulatingwith the cricoidcartilageasdescribed.
352 MEMOIRS OP THE QUEENSLAND MUSEUM
FIG. 1.LongitudinalsectionofHumpbackWhalelarynxUM7303)inmedialaspect(thyroidcartilageremoved).
(A) epiglottic cartilage: (B) fibrous ailachment lo thyroid cartilage; (C) arytenoid cartilage - corpus; (D)
arytenoidcartilage -rostralend;(E)cricoidcartilage;iF)tracheallumen;(C.)fundusoftheventraldiverticulum;
(H)neckoftheventral diverticulum; (1) thyroarytenoidmuscle; (J)interarytenoid fibroelasticconnection.
Thebody ofthe arytenoid lay largely within the tilages were not fused but "jumbled". The car-
arch of the cricoid. A short thick process ex- tilages were deficient vcntrally where they had
tended from the cricoarytenoid articulation to rounded ends. The ventral diverticulum was
join the body ofthe cartilage in its middle third. recessed into the defect between these ends, the
The body was a banana shaped mass 15cm long tracheal lumen being effectively divided into
with the rostral and the caudal extensions. two passages.
Caudal processeswere connected in the midline A pouch (ventral diverticulum) opened into
by a thick fibro-elastie band. The beak shaped the laryngeal lumen by a longitudinal slit on its
rostral processes were concave vcntrally and floor between the medial borders of the
togetherwerealmostembracedby theepiglottis. arytenoidcartilages.There is no humancounter-
Theepiglottistogetherwith therostral processes part. Itwas 10cm longand was3 cm in diameter
of the arytenoids and the arycpiglottic folds atthe fundus.Thewall wasfibrousandappeared
formed the arytenoepiglottideal tube. The nondistensible. There were some shallow pock-
medialbordersofthecorpuswere almost flatand ets in the fundus and the whole wascovered by
covered with tough skin. They approximated in a thick muscular mass. The fundus invaginated
the midline. Some accounts refer to part of this into the tracheal lumen on its ventral side and
body as the cuneiform cartilage (Hosokawa, appeared to ail but obliterate that lumen.
1950:28). A partial cleft in this specimen sug-
geststhatthecuneiform and arytenoid cartilages
maybefused,therostralprocessrepresentingthe INTERPRETATION
cuneiform cartilage.
The epiglottis was 15 cm long and roughly L the aryteno cpiglottideal tube appeared to
spoon-shapedconcavedorsally. It was relatively form a conduit to carry the air stream from the
clasticandattachedbya thick fibrousband tothe posterior choanae to the laryngeal inlet.
thyroid cartilage near its cranial notch. The in- 2, the airstrcam appeared to be directed into
tegument on the luminal side had thick lon- the ventral diverticulum (Fig. 2). The opening
gitudinal grooves which seemed almost to into the diverticulum may well be closed during
interdigitate with those on the adjacent surface normal inspiration.
ofthe arytenoid. 3, air passing into the trachea must pass be-
The trachea was comparatively short being tween the flattened margins of the bodies of the
approximately 4cm long from the cricoid plate adjacent arytenoid cartilages.
to the bifurcation. Dorsally the proximal car- 4, theventral diverticulum seemedunlikely to
HUMPBACK WHALE LARYNX 353
FIG. 2. Longitudinal section of Humpback Whale larynx (JM7303) in media! aspect lo show course ofair
stream into trachea.
bedistensibleandasareservoirwouldhavebeen functionasavalveabletoisolatethesupraglottic
ofrelatively small size. airspace from that in the thorax.
5, air expelled from the diverticulum would 7, among cetaceans ventral diverticula have
apparently pass over the free margins of the been described only in baleen whales (Slij-
arytenoids and through the arytenoepiglottidcal per,1962:147).
tube into the nasopharynx. 8, baleen whales produce sounds organised
6. the ventral diverticulum could apparently intoacomplex form and distinctfromthe repcti-
l I
FIG. 3. Schematic drawing laryngeal inlet (i) humpback whale; (ii) human. (A)epiglottis; (B) arytenoid; (C)
glotticchink.