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.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
18. 19. 20.
Magendie F: Memoire sur l'usage de l'Epiglotte dans la Deglutition. Paris, Mequignon-Marvis, 1813 Warwick R, Williams P, eds: Gray's Anatomy: 35th British Edition. Philadelphia, Saunders, 1973, p 1176 Ardran GM, Kemp FH: The mechanism of swallowing. Proc R Soc 44: 1038, 1951 Ardran GM, Kemp FH: The mechanism of the larynx. Part II: The epiglottis and closure of the larynx. Brit J Radiol 40: 372, 1967 Ardran GM, Kemp FH, Lind J: A cineradiographic study of bottle feeding. Brit J Radiol 31: 11, 1958 Negus VE: The Comparative Anatomy and Physiology of the Larynx. London, William Heinemann Medical Books, 1949 Negus VE: The function of the epiglottis. J Anat 62: 1, 1927 Crelin ES: Anatomy of the Newborn: An Atlas. Philadelphia, Lea & Febiger, 1969 Crelin ES: Functional Anatomy of the Newborn, New Haven, Yale University Press, 1973 Laitman JT, Crelin ES: Postnatal development of the basicranium and vocal tract region in man, Symposia on the Development of the Basicranium, Edited by JF Bosma In press Negus VE: The Mechanism of the Larynx. St. Louis, C. V. Mosby, 1929 Birrell JF: The Ear, Nose and Throat Diseases of Children. London, Cassell and Co., 1960 Boyd ME: Congenital atresia of posterior nares. Arch Otolaryngol 41: 261, 1945 Fearon B, Dickson J: Bilateral choanal atresia in newborn. Plan of action. Laryngoscope 78: 1487, 1968 Flake CG, Ferguson CF: Congenital choanal atresia in infants and children. Arch Otolaryngol 81: 425, 1965 Ardran GM, Kemp FH: A radiographic study of movements of the tongue in swallowing. Dent Prac 5: 252, 1955 Ardran GM, Kemp FH: The mechanism of change in the form of the cervical airway in infancy. Medical Radiography and Photography 44: 26, 1968 Bosma JF: Anatomic and physiologic development of the speech apparatus. Human Communication and its Disorders, Edited by DB Tower, New York, Raven Press, 1975, pp 469-481 Bosma JF, Truby HM, Lind J: Cry motions of the newborn infant. Acta Paediatr Scand 49: Suppl. 61, 1966 Pressman JJ, Keleman G: Physiology of the larynx. Physiol Rev 35: 506, 1955.
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
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.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
18. 19. 20.
Magendie F: Memoire sur l'usage de l'Epiglotte dans la Deglutition. Paris, Mequignon-Marvis, 1813 Warwick R, Williams P, eds: Gray's Anatomy: 35th British Edition. Philadelphia, Saunders, 1973, p 1176 Ardran GM, Kemp FH: The mechanism of swallowing. Proc R Soc 44: 1038, 1951 Ardran GM, Kemp FH: The mechanism of the larynx. Part II: The epiglottis and closure of the larynx. Brit J Radiol 40: 372, 1967 Ardran GM, Kemp FH, Lind J: A cineradiographic study of bottle feeding. Brit J Radiol 31: 11, 1958 Negus VE: The Comparative Anatomy and Physiology of the Larynx. London, William Heinemann Medical Books, 1949 Negus VE: The function of the epiglottis. J Anat 62: 1, 1927 Crelin ES: Anatomy of the Newborn: An Atlas. Philadelphia, Lea & Febiger, 1969 Crelin ES: Functional Anatomy of the Newborn, New Haven, Yale University Press, 1973 Laitman JT, Crelin ES: Postnatal development of the basicranium and vocal tract region in man, Symposia on the Development of the Basicranium, Edited by JF Bosma In press Negus VE: The Mechanism of the Larynx. St. Louis, C. V. Mosby, 1929 Birrell JF: The Ear, Nose and Throat Diseases of Children. London, Cassell and Co., 1960 Boyd ME: Congenital atresia of posterior nares. Arch Otolaryngol 41: 261, 1945 Fearon B, Dickson J: Bilateral choanal atresia in newborn. Plan of action. Laryngoscope 78: 1487, 1968 Flake CG, Ferguson CF: Congenital choanal atresia in infants and children. Arch Otolaryngol 81: 425, 1965 Ardran GM, Kemp FH: A radiographic study of movements of the tongue in swallowing. Dent Prac 5: 252, 1955 Ardran GM, Kemp FH: The mechanism of change in the form of the cervical airway in infancy. Medical Radiography and Photography 44: 26, 1968 Bosma JF: Anatomic and physiologic development of the speech apparatus. Human Communication and its Disorders, Edited by DB Tower, New York, Raven Press, 1975, pp 469-481 Bosma JF, Truby HM, Lind J: Cry motions of the newborn infant. Acta Paediatr Scand 49: Suppl. 61, 1966 Pressman JJ, Keleman G: Physiology of the larynx. Physiol Rev 35: 506, 1955.
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
