THE YALE JOURNAL OF BIOLOGY AND MEDICINE 50 (1977)
The Function of the Epiglottis
in Monkey and Man'
J.T. LAITMAN, E.S. CRELIN, AND G.J. CONLOGUE
Yale University School of Medicine, New Haven, Connecticut
Received July 16, 1976
In stumptail monkeys from birth to adulthood, and in very young human infants, the epiglottis serves to
guide the larynx upwardly behind the soft palate so it can lock into the nasopharynx and remain there during
respiration. After early infancy in man the attainment of a larynx-nasopharynx connection is uniquely lost,
causing the epiglottis to have no essential function.
The function of the epiglottis has been debated ever since Magendie [1] first
contested its action as a flap to cover the larynx and prevent the accidental entrance
of food. The most recent edition of Gray's Anatomy [2] emphasizes that the epiglottis
is degenerate in function, that normal deglutition can occur if it is destroyed by
disease, and that it is not essential in either respiration or phonation in numans. In
contrast, a team of British radiologists [3,4,5,] stress that epiglottic positioning is a
crucial element in the last stages of deglutition.
Negus' [6] work on the comparative anatomy of the larynx shows that while certain
snakes have a rudimentary yellow elastic cartilage similar to the epiglottis, the
epiglottis is essentially a mammalian structure. His postmortem dissections of all
types of mammals indicated that the epiglottis passes up behind the soft palate to
guide the locking of the larynx directly into the nasopharynx. This provides a direct
air channel from the external nares through the nasal cavities, nasopharynx, larynx
and trachea to the lungs. Food could pass on either side of the interlocked larynx and
nasopharynx via the isthmus faucium, then through the piriform sinuses to the
esophagus without interfering with the passage of air through the patent airway.
Negus concluded that the function of the epiglottis in mammals was to subserve the
sense of smell by allowing an individual to essentially breathe and eat at the same
time [6,7].
Negus studied the cadavers of non-human primates and found that the epiglottis
could be placed in direct contact with the soft palate. He could not do this in mature
human cadavers because the posterior third of the tongue forms the anterior wall of
the pharynx and the larynx is situated in a low position in the neck. This results in the
epiglottis being too far from the soft palate to make any contact even when there is
maximum laryngeal elevation (i.e., during deglutition). He mentioned that it was
possible to approximate the epiglottis and soft palate in human newborn cadavers
without attaching any possible developmental or functional significance to this fact.
More recent anatomical studies by Crelin and Laitman and Crelin [8,9,10] show that
the anatomy of the upper respiratory tract of primates in particular, and of mammals
in general, closely approximates that of human newborn and very young infants.
43
'Supported by the Crippled Children's Aid Society, New Haven, Connecticut.
Please address reprint requests to: J.T. Laitman, Section of Gross Anatomy, 333 Cedar Street, New Haven CT 06510
Copyright i' 1977 by The Yale Journal of Biology and Medicine, Inc.
All rights of reproduction in any form reserved.
44
LAITMAN ET AL.
Primates are usually habitual nose breathers [11], whereas mature humans frequently
breathe alternately through either the mouth or the nose. Clinical studies, however,
reveal that human newborn and very young infants are obligate nose breathers.
Pathologic conditions such as a congenital blockage of the posterior nares (choanal
atresia) which prevents nasal breathing, often results in the death of an otherwise
perfectly normal baby [12,13,14,15]. Our postmortem dissections show that in human
newborn and infants up to four years of age the epiglottis can easily be made to
approximate the soft palate. A larynx can be manually locked into the nasopharynx
in young human infant cadavers which closely resembles that usually found in
mammalian cadavers in general. Therefore, this indicates that the epiglottis of the
young human infant also functions to guide the interlocking of the larynx into the
nasopharynx.
To be sure that this actually occurs in life, much of Negus' work and our own was
reinvestigated using radiological techniques on living individuals. Studies by Ardran
et al. [3,4,5,16,17] and Bosma [18,19] using cineradiography to study young human
infants swallowing barium in water and milk, did not describe the interlocking of the
larynx and pharynx occurring at any time in any of their subjects. In fact, during
quiet respiration their descriptions and illustrations show the epiglottis is erect but
not making any contact with the soft palate. It is extremely difficult to discern the soft
tissue structures, such as the epiglottis and soft palate, on cineradiographic films
because of their high radiolucency. Therefore in our studies of still and cineradiographic films of infant and adult humans during swallowing, phonation and quiet
respiration, we included monkeys that had the tip of their soft palate and epiglottis
"tagged" with tantalum clips (Fig. 3).
A newborn, 1¼2 year old, 3½/2 year old, and 512 year old adult, stumptail macaque
(Macaca arctoides) were placed under light anesthesia and a small sterile Weck
tantalum hemoclip was attached to both the tip of the uvula of the soft palate and the
distal tip of the epiglottis. When each regained consciousness we recorded lateral
views of the head and neck on still and cineradiographic film during various stages of
vocalization and quiet respiration, and during swallowing of saliva, milk, water, and
barium (micropaque mixture) in water and milk. Cineradiographic and still films of
lateral views of 17 newborn humans were made by pediatric radiologists as part of
diagnostic procedures for various respiratory and intestinal disorders. The films
showed the babies during comparable stages of oropharyngeal activity. Twelve of the
newborns suckled a barium-water mixture, four suckled milk and one a bariumwater mixture which was administered through a small plastic catheter into the
nasopharynx via the nose. Lateral views of hospital diagnostic cineradiographic and
still films of 12 adult humans showing comparable oropharyngeal activity were also
studied. Six of the adults swallowed a barium-water mixture.
The radiographic films revealed that the macaques of all ages behaved in essentially
the same manner. They showed no adverse reactions to the presence of the clips when
compared to monkeys performing the same functions without clips. During quiet
respiration, the larynx was locked directly into the nasopharynx, providing a continuous larynx-nasopharynx connection. The animals were obligate nose breathers that
reacted violently to any attempt to obstruct their nasal airway. During deglutition the
epiglottis and soft palate were also seen to be in overlapping contact providing the
patent airway (Fig. 3). A momentary separation frequently occurred that was most
often related to the density of the liquid being swallowed. While drinking water the
animals usually kept the larynx locked into the nasopharynx. When swallowing milk
EPIGLOTTIS IN MONKEY AND MAN
45
and the barium mixtures a momentary unlocking of the larynx from the nasopharynx
usually occurred as the bolus passed from the piriform sinuses into the entrance of
the esophagus. At this moment the soft palate would become elevated and abut the
posterior pharyngeal wall, shutting off the nasopharynx. As soon as the bolus passed
into the esophagus the larynx was immediately locked into the nasopharynx. During
vocalization or crying a larynx-nasopharynx connection did not occur.
Simultaneous viewing of the cineradiographic films of the human newborns with
those of the monkeys in frame by frame comparisons allowed us to analyze the
similarities and differences. The attachment of the clips to the tip of the uvula and
epiglottis permitted positive localization of these structures at all times in the
monkeys. The marking of these structures in the human specimens with barium,
though not as effective as the tantalum clips, was nevertheless quite useful in
discerning the relationship of the epiglottis and soft palate. On choice still radiographic films the epiglottis and soft palate could be clearly seen due to their own
contrasting density (radiopacity).
The human newborn was seen to behave in quiet respiration identically to that of
the macaques (Figs. 1 and 2), with the larynx locked into the nasopharynx. During
deglutition the human newborn again behaved in a similar manner to that of the
macaque. The larynx was locked into the nasopharynx at the commencement of
swallowing. It would usually remain there when only saliva was swallowed. When
milk or the barium-milk mixture was swallowed a momentary separation often
occurred when the bolus passed into the esophagus, with a concomitant elevation of
the soft palate to wall off the nasopharynx. Immediate interlocking of the larynx with
the nasopharynx occurred to re-establish a patent airway. No larynx-nasopharynx
locking occurred during vocalization and crying.
The cineradiographic and still films of the adult human revealed that no contact
occurred between the epiglottis and soft palate. During quiet respiration the epiglottis remained erect (Fig. 4). During deglutition the arytenoid cartilages tilted forward
to cause the corniculate cartilages to approximate the tubercle at the base of the
epiglottis. This closed off the laryngeal vestibule as the soft palate was elevated to
close off the nasopharynx. As the bolus of barium-water mixture passed from the
oral cavity into the pharynx the epiglottis invariably became folded downward over
the tilted arytenoid cartilages. Apparently this downward folding of the epiglottis is
not essential to prevent food from entering the larynx because a large part of it can be
removed with no adverse effects [20].
Thus, the epiglottis in the monkey and the young human infant is a structure which
serves to guide the larynx upwardly behind the soft palate so it can lock into the
nasopharynx. It is presumed that this is its function in all adult mammals except
man. In man after birth there is a gradual descent of the posterior third of the tongue
into the neck to form the anterior wall of the pharynx. The larynx also descends to a
lower position in the neck which ultimately results in the larynx opening into the
lowest part of the pharynx. This allows the pharynx in man to serve as a part of the
vocal tract for the production of articulate speech [9,10]. Based on our cadaver
dissections of children who died between birth and puberty, it appears to be around
3¼2 to 4 years of age when these uniquely human structural modifications of the vocal
tract reach a point that will no longer permit the epiglottis to overlap the soft palate.
However, when the human infant actually ceases to be a functionally obligate nose
breather, who no longer locks his larynx into his nasopharynx, has yet to be determined.
FIG. 1. Diagram of a human newborn showing a larynx locked into the
nasopharynx during quiet respiration.
FIG. 2. Still lateral radiograph of a human newborn with larynx locked into the
nasopharynx.
FIG. 3. Still lateral radiograph of lAj year old stumptail macaque with a metal clip attached to the uvula of the soft
palate and the distal tip of the epiglottis. The larynx is locked into the nasopharynx while suckling a barium-water
mixture.
No
FIG. 4. Still lateral radiograph of an adult human during quiet nasal respiration. There is a wide interval between the
soft palate and the epiglottis. (I) Tip of uvula of the soft palate, (2) distal tip of the epiglottis, (3) nipple of bottle
containing barium-water mixture.
48
LAITMAN ET AL.
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We thank Drs. D. Snyder, G. Redmond, Jr., L. Kier, C. Sasaki and J. Maas for their advice and assistance in selecting,
maintaining and working with the monkeys. We also thank J. Baulu, G. Warmoth, A. Mead, D. Weinstein and M. Cebul
for their assistance in handling and caring for the animals.
Cineradiographic and still films of the human newborn and children were provided by Drs. J.F. Bosma, E. Effmann, R.
Ablow, C. Hodson, M. Ozonoff, E. Yanagisawa, and H. Smith.
J.T. Laitman
E.S. Crelin
G.J. Conlogue
Human Growth and Development Study Unit, Anatomy Division
Yale University School of Medicine
New Haven, Connecticut 06510