Human Embryology and Morphology 14

From Embryology

Keith, A. Human Embryology And Morphology (1921) Longmans, Green & Co.:New York.

Human Embryology and Morphology: 1 Early Ovum and Embryo | 2 Connection between Foetus and Uterus | 3 Primitive Streak Notochord and Somites | 4 Age Changes | 5 Spinal Column and Back | 6 Body Segmentation | 7 Spinal Cord | 8 Mid- and Hind-Brains | 9 Fore-Brain | 10 Fore-Brain Cerebral Vesicles | 11 Cranium | 12 Face | 13 Teeth and Mastication | 14 Nasal and Olfactory | 15 Sense OF Sight | 16 Hearing | 17 Pharynx and Neck | 18 Tongue, Thyroid and Pharynx | 19 Organs of Digestion | 20 Circulatory System | 21 Circulatory System (continued) | 22 Respiratory System | 23 Urogenital System | 24 Urogenital System (Continued) | 25 Body Wall and Pelvic Floor | 26 Limb Buds | 27 Limbs | 28 Skin and Appendages | Figures


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Chapter XIV. The Nasal Cavities and Olfactory Structures

Evolution of the Nasal Cavities

Although the sense of smell is a minor one in the economy of the human body, it is very evident that in the root-stock from which mammals have been evolved the olfactory organ must have held a foremost place amongst the sensory structures. We have seen that the great superstructure of the brain rests on the primary ganglia connected with the olfactory nerves. When now we examine the changes connected with the development of the nose and nasal cavities in the human embryo, we shall see, behind the complicated processes at work, a recapitulation of conditions which are to be seen in animals occupying a very low position in the vertebrate kingdom. At the end of the 4th week the olfactory membrane appears as two plaques of ectoderm in contact with the under surface of the fore-brain (Figs. 155, A, 192, A) ; in the 5th week the plaques or plates become two pits — right and left, the usual condition in fishes ; in the 6th week each pit becomes connected with the primitive mouth or stomodaeum by a groove — a condition seen in the dog-fish ; in the 6th and 7th weeks the pit is deepened and its opening becomes turned towards the stomodaeum owing to the growth of its lateral and mesial margins which form the lateral and mesial nasal processes (Fig. 155). The processes unite in the manner already described and a nasal cavity similar to that of the air-breathing or dipnoan fishes is established. In the 7th and 8th weeks the cavity of the pit is rapidly enlarged ; free communication with the mouth is established ; the nasal cavity has then become, as in amphibians, the functional vestibule of the respiratory system. In the 3rd. month the palate is complete, and the stage peculiar to mammals thus established.

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Fig. 192, A. The Olfactory Pit and Face of an Embryo in the 5th week of development. (After Broman.)

Fig. 192, B. The Olfactory Pit and Facial Processes in an Embryo in the 6th week of development. (After Hochstetter.)


In tracing the development of structures subservient to the sense of smell, the following elements have to be dealt with :

  1. The olfactory sense epithelium and olfactory nerves ;
  2. The parts of the brain concerned with the sense of smell ;
  3. The capsule which contains the olfactory epithelium ;
  4. The respiratory tract of the nasal cavities.

1. Origin of the Olfactory Sense Epithelium

At the end of the 4th week, a small area of the ectoderm lying under the fore-brain becomes demarcated on each side, to form the olfactory plates.[1] Around these two plates the lateral and mesial nasal processes grow up (Fig. 193), the plates becoming at the same time invaginated to form the olfactory pits. With the growth of the nasal processes the cavities of the expanding olfactory pits or pockets come to occupy a space on the roof of the stomodaeum, their openings being turned towards that cavity. The ectodermal lining becomes the epithelial membrane of the nasal cavities. A small island is detached from each olfactory plate to form the basis of Jacobson's organ (Fig. 193). The sense epithelia in the olfactory area behave as nerve cells and send out nerve processes which form arborescences round the neural cells of the outgrowing olfactory bulb (Fig. 194). The olfactory nerves are thus formed. At first the olfactory plates are directly in contact with the cerebral vesicle, but later on they are separated by the formation of the cerebral membranes and cribriform plates.

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Fig. 193. The Olfactory Pit and Nasal Processes in a Human Embryo about 5 weeks old. (After Kollmann.)

In the foetus the olfactory or sense epithelium is relatively extensive, as is the case in mammals with a keen sense of smell. It descends almost to the lower border of the middle turbinate on the outer or lateral wall, and to the junction of the upper two-thirds with the lower third on the mesial or septal wall. In the adult the distribution is much restricted — occupying areas only about one finger breadth in extent below the cribriform plate.


2. The Olfactory Lobe

As the olfactory pits are being thrust into the roof of the stomodaeum during the 6th week, the anterior part of the floor of the cerebral vesicles are growing out as hollow protrusions to form the olfactory vesicles. At the end of the 3rd month the olfactory vesicle has assumed the form shown in Fig. 194. Its cavity is at first continuous with that of the cerebral vesicle, but this connection is lost in the 3rd month ; it becomes solid, and forms the olfactory bulb and tract (Fig. 196).

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Fig. 194. The Mesial Aspect of the Brain of a Human Foetus, 5.5 months old, showing the Olfactory Lobe. A, olfactory bulb ; B represents the paraterminal part of the rhinencephalon.


The tip of the anterior horn of the lateral ventricle marks the point at which the cavity of the olfactory lobe communicated with the cerebral vesicle.

The Rhinencephalon

The Rhinencephalon is made up of the parts of the cerebrum which are primarily connected with smell. These parts are best seen in a typical mammalian brain such as is shown in Fig. 195. They are, following the classification of Elliot Smith : (1) the olfactory bulb and peduncle or tract, both of which are developed from the olfactory lobe ; (2) the olfactory tubercle, represented in the human brain by a small area behind the trigone ; (3) the paraterminal body (Figs. 194, 195) which is represented in the human brain by the gyrus subcallosus and septum lucidum ; (4) the hippocampal formation represented in the human brain by the supra-callosal gyrus, gyrus dentatus, hippocampus and fornix (Fig. 196) ; (5) the pyriform lobe (the uncus of the human brain) ; (6) the anterior perforated space. In man these parts are reduced in size owing to (1) his less acute sense of smell ; (2) the great development of the corpus callosum and mantle of the brain. The rhinencephalon represents the oldest part of the brain, and its grey matter differs from the rest of the cortex in structure.

Morphology of the Olfactory Neural Elements

If the olfactory area of ectoderm were to adhere to, and form part of, the olfactory bulb, then the olfactory vesicle would be comparable to the optic vesicle, the rods and cones representing the olfactory epithelium, the ganglion cells of the olfactory bulb those of the retina, while the lateral and mesial olfactory tracts would correspond to the optic tracts. This homology is impaired by the fact that the fibres of the lateral olfactory tract end, not in a ganglionic mass, but in true cortex — that of the pyriform lobe or uncus (Fig. 195). The pyriform cortex is linked up with the gyrus dentatus by a second relay of fibres, while the dentate gyrus is connected in turn with the hippocampal cortex by a third relay. The fornix and the hippocampal commissure (see p. 122) represent the association and commissural system of the hippocampal formation. The anterior commissure was originally made up of fibres passing from one olfactory bulb to the other (p. 121). Fibres in the mesial root of the olfactory tract reach the dentate gyrus by means of the fornix and supra-callosal striae.

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Fig. 195. The mesial Aspect of a typical Mammalian Cerebrum shoeing the parts of the Rhinencephalon. (Elliot Smith.)

The Nasal Cavities

The nasal cavities are formed by the expansion of the olfactory pockets within the substance of the three developmental masses which surround each of them — the mesial nasal, lateral nasal and maxillary processes. When these processes unite in the 7th week, the primitive nasal cavity rapidly expands, and an opening temporarily closed is reformed in its fundus or floor, the primitive choanae, situated in the roof of the mouth (Fig. 170). The choanae are separated by the primitive nasal septum, and are at first in front of the pituitary outgrowth — Rathke's pocket (Fig. 197). In the latter part of the 2nd month and the earlier half of the 3rd the primitive nasal septum and the choanae on each side of it, extend their dimensions, until the posterior border of the septum reaches and involves the mouth of Rathke's pocket (J. E. Frazer). In this manner the nasal septum is secondarily extended, and the nasal cavities greatly deepened (Fig. 197). At the same time the floor of the nasal cavities is prolonged backwards by the formation of the secondary palate, and the secondary choanae are established within the region of the naso-pharynx before the end of the 3rd month. The process of chondrification begins in the lower part of the lateral nasal process during the period at which the secondary palate is being formed. The chondrification of the lateral mass of the ethmoid and other parts of the olfactory capsule have already been described (p. 149).

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Fig. 196. The parts of the Rhinencephalon in the Human Brain.

Development of Turbinates and Air Sinuses

Before cartilage has actually been formed in the walls of the primitive nasal cavities[2] (Formation of Antrum). See also references, p. 135., linear outgrowths of the lining epithelium are observed to occur in the lateral wall and roof. These outgrowths give rise to the meatuses of the nose — the inferior under the maxillo-turbinal appearing first, about the 8th week, the superior last, about the 12th week. In the lateral wall of the nasal cavity of a foetus 20 mm. long and in the 8th week of development Dr. Milne Dickie[3] found only two linear depressions — ^the lower representing the inferior meatus, the upper the hiatus semilunaris (ethmoidal infundibulum. Fig. 198). The turbinate processes are thus carved out of the lateral wall and roof of the nasal cavity. The usual number is five in mammals, but in man the 4th and 5th are only temporary. The inferior or maxilloturhinate is developed on the lateral wall, but the middle and upper appear on the roof and septal wall, their lateral position being attained in the course of development. The sphenoidal turbinate also belongs to the ethmoidal series, but becomes applied to the body of the presphenoid. The turbinates and meatuses are developed in connection with respiration. They increase, it is true, the olfactory area, but their chief use is apparently to filter and warm the inspired air.


The manner in which the nasal mucous membrane pushes its way from the middle meatus into the maxillary process to form the antrum of Highmore has been already described (p. 173). The other air sinuses — ^the frontal, lachrymo-ethmoidal, anterior, middle and posterior ethmoidal, and sphenoidal sinuses — six in all, arise in the same way as the antrum, but begin, with the exception of the last named, to enlarge at a much later date. Although they begin to bud out about the time of birth, they assume their active growth in the earlier years of puberty, and reach their full size before the 30th year.

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Fig. 197. The Primitive Nasal Cavities and Ciioanae at the end of the 6th week. The formation of the secondary septum and palate are indicated. (After J. E. Frazer.)


At birth, the lateral mass of the ethmoid is a thin plate, carrying the superior and middle turbinate processes, which almost fill the nasal cavity (Figs. 169, 198). The entire ethmoid is narrow, and hence the proximity of the eyes in children. Beneath the middle turbinate is a thumbnail-like impression — the hiatus semilunaris, or ethmoidal infundibulum, one of the earliest formations (8th week). The maxillary sinus buds out near its posterior end, the point at which the bud arises becoming the site at which the sinus opens in the middle meatus (Fig. 199). The uncinate process of the lateral mass of the ethmoid forms the prominent lower margin of the hiatus (Fig. 198). A second opening may be present below the level of the uncinate process, or this may be the only one developed.


In Fig. 198 part of the middle turbinate has been removed to expose the frontal recess of the middle meatus — an expansion of the meatus formed in the 4th month of foetal life. At birth[4] four furrows are present — representing the buds of air sinuses. One, or occasionally two, of these enlarge to form the frontal sinuses, the others becoming cells of the ethmoid. The duct or mouth of the frontal sinus may become secondarily continuous with the hiatus semilunaris or the bud of the frontal sinus may arise from the upper end of the hiatus. The bud of the frontal sinus, as it expands, pushes its way into the frontal bone, separating the outer from the inner lamella. The bud is formed in the first year, but is nascent until the fifth. A second frontal bud may arise and partially or completely supplant the primary frontal outgrowth. As a rule, by the 25th year the sinus reaches outwards over the inner two-thirds of the orbital roof, and is an inch or more both in height and depth at its mesial part. It is smaller in women than in men, but it may be, and often is, arrested at an early stage of development, or it may be absent altogether. The size of the glabellar prominence is no index to its development.


The stalk of the frontal bud forms the infundibulum or naso-frontal duct, which is narrow, half an inch long, and difficult of catheterization from the nose. Into it open (or sometimes into the hiatus) the lachrymoethmoidal and anterior ethmoidal cells which surround the infundibulum. They are developed as outgrowths from the infundibulum (Fig. 199). Occasionally the maxillary sinus, as is frequently the case in the gorilla, sends a process to form part of the frontal sinus, and hence there may be a communication between the sinus and the antrum.

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Fig. 198. The Lateral Wall of the Nasal Cavity of a child at birth. (J. Parsons Schaeffer.)


The development of the frontal sinuses and supra-orbital ridges leads to a marked change in the face at puberty. By the formation of the frontal sinuses the basal area of the skull, to which the face is attached, is largely increased in extent. Such an increase is necessary to support the palate, which grows rapidly in size at puberty. Up to the fifth year the upper jaw has to carry only ten milk teeth ; in the adult it has to carry sixteen permanent teeth. To support these the face and palate have to be enlarged. The formation of the frontal sinus gives the necessary increase in the area of the base of the skull for their support. It should be remembered that the growth of the brain and of the cranial cavity is comparatively slight after the fifth year. Only the gorilla and chimpanzee show an arrangement of frontal and ethmoidal sinuses comparable to that of man.


Above the hiatus lies the bulla ethmoidalis, which is inflated by, and commonly carries the opening of, the middle ethmoidal cell (Fig. 199). The posterior ethmoidal sinus opens beneath the superior turbinate process, and IS developed from the superior meatus. The ethmoidal sinuses are produced in the cartilage of the ethmoidal or lateral nasal plate (Fig. 175). They inflate the ossifying cartilaginous plate until it becomes a cellular mass, thus increasing the breadth of the intra-orbital septum. The sphenoidal sinus (Fig. 199) is formed during the 3rd month by the mucous membrane growing into and expanding the sphenoidal turbinate bone, which is a small, slightly ossified cartilage lying beneath the presphenoid at birth, and forming the uppermost (sixth) of the nasal turbinate processes.

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Fig. 199. A Diagram of the Lateral Wall of the Nasal Cavity, showing the position of the Air Sinuses. The parts beneath the turbinate processes are indicated by stippled lines.


Latterly the sinus grows into and expands the presphenoid and part of the basi-sphenoid, the sphenoidal turbinate remaining as its anterior wall. The sphenoidal turbinate is a detached part of the ethmoidal cartilage.


It will thus be seen that all the nasal air sinuses are produced primarily by a budding outwards of the nasal mucous membrane into the cartilaginous basis of the lateral nasal processes. Disease may readily spread to these sinuses from the nasal cavities. By means of the sinuses the area of the face is increased to support the adult palate bearing the permanent teeth. Most of them open on the respiratory tract of the nasal cavity. They are ventilated with every breath. They act also as resonance chambers.


Vestigial Turbinates

There is frequently to be seen in the adult one, or even two, secondary meatuses above the superior ; these are constantly present in the chimpanzee and in mammals with a keen sense of smell. In the human foetus of four months six turbinates are usually present, besides secondary processes in the meatuses beneath them. The upper most of these, the sixth, becomes the sphenoidal turbinate ; the fifth disappears ; the third and fourth may remain separate or become united ; the first and second form the inferior or maxillo-turbinal and middle turbinate processes. The agger nasi (naso-turbinal, Fig. 198), in front of the attachment of the middle turbinate process, is a vestige of the nasoturbinal, a process well developed in most carnivora and animals with a strong scent. The uncinate process, which forms the lower border of the hiatus semilunaris, is continuous at its base with the naso-turbinal. Through the hiatus semilunaris acting as a gutter, the antrum may become a cesspool for a suppurating frontal sinus.

Organ of Jacobson

Mention has already been made of the organ of Jacobson[5] — situated on the nasal septum above the naso-palatine canals. During development (Fig. 193) a part of the olfactory plate becomes detached, and is afterwards invaginated in a pocket in the septum and guarded by a scroll of cartilage. It reaches its maximum development in the human foetus at the 5th month, and afterwards becomes a mere vestige- — often unrecognizable. It sometimes persists and forms a very evident structure on the septum. A pocket can usually be seen on the septum at birth (Fig. 200). This special development of the olfactory organ is highly developed in all herbivorous vertebrates in whom the nasopalatine canals are widely open, and thus the juices and odours of the mouth have free access to the organ. Professor Broman[6] has suggested that it is for sampling substances dissolved in fluid, as is the case with the olfactory organ of fishes.

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Fig. 200. Nasal Septum of a Child at Birth, showing a rod inserted in the pocket of Jacobson's organ {A). B, closed naso-palatine canal; C, presphenoid ; D, vomer.


Nervus Terminalis

Amongst the fibres of the olfactory nerve[7], particularly in the branch to Jacobson's organ, there occur nerve cells, apparently of the same nature as those belonging to the sympathetic system. From these cells issue fibres which connect the olfactory areas of sense epithelium with grey matter near the lamina terminalis of the fore-brain. The fibres constitute the nervus terminalis which is well developed in low vertebrates and of which there remains a vestige in man.


Nasal Duct

Although in no way connected with the sense of smell, the nasal duct[8] is closely related to the nasal cavities. It is formed between the lateral nasal and maxillary processes (Figs. 155, 193). It is laid down as a solid epithelial cord along the naso-maxillary groove at the end of the second month. It becomes canaliculized during the 3rd month.[9] Three bones bound it : the superior maxilla on the outer side, formed in the maxillary process ; the inferior turbinate, formed in the cartilage of the lateral nasal process, and the lachrymal, formed over the lateral nasal cartilage, bound it on the inner side. The formation of the palate cuts the duct off from the mouth. The hamulus of the lachrymal varies much in size, and is the vestige of a large process, which in lower primates enters into the formation of the inferior margin of the orbit. This pars facialis sometimes occurs in man (Fig. 201). Occasionally the frontal and superior maxillary bones may push towards each other between the lachrymal in front and lateral mass of the ethmoid behind, and thus form a frontomaxillary articulation on the inner wall of the orbit.

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Fig. 201. Showing on the Inner Wall of the Orbit (1) the Position of the Infundibuliim, (2) the Pars Facialis Lachrymalis.


Malformations of the Nose

In Figs. 156 and 166 two malformations of the nose are represented. In Fig. 156 the rare condition is shown in which one olfactory pit and its corresponding processes form a polypoid body ; in Fig. 202 the condition of Cyclops, where Iboth nasal cavities are enclosed in a proboscis is represented. The eyes are also fused. The condition of the facial skeleton in such a case is represented in Fig. 166. In such cases there has been an arrest of growth of the cephalic end of the embryonic plate, with a fusion of the olfactory bulbs and also of the optic vesicles. The two olfactory plates and pits are united in a single median structure. In this condition we seem to have represented a pure developmental abnormality — not a reversion to some past stage in evolution (see p. 161).


Two other malformations require mention. During the 3rd, 4tli and 5th months of foetal life an epithelial plug is formed within the anterior nares — where the cutaneous and nasal epithelial coverings meet. In rare cases the plug becomes organized, and forms a dense septum within the nares. A similar obstruction, often containing bone, may be formed near the posterior nares. The posterior narial occlusion represents an organization and persistence of the epithelial membrane which at first closes the primitive choanae (see p. 170).

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Fig. 202. Median Sagittal Section of the Head and Face in a Case of Cyclops. A, frontal bone ; B, single median nasal cavity contained in a proboscis formed by the nasal processes ; C, median or fused eye ; D, palate formed by the maxillary processes only ; E, median cerebral vesicle ; F, single optic nerve ; G, Eustachian tube ; E, palate bone.



  1. For development of Nasal Cavities see J. E. Frazer, Journ. Anat. and Physiol. 1912, vol. 46, p. 416 ; K. Peter, Ergebnisse der Anat. 1911, vol. 20, p. 43.
  2. See Keith, Proc. Anat. Soc. Great Brit, and Ir. May, 1902, Brit. Journ. Dent. Sc. 1902, vol. 45, p. 529 ; J. Parsons Schaeffer, Amer. Journ. Anat. 1912, vol. 13, p. 1;Ibid. Amer. Journ. Anat. 1912, vol. 13, p. 1 (Formation of Nasal Duct) ; Ibid. Amer. Journ. Anat. 1910, vol. 10, p. 313
  3. Journ. Anat. 1914, vol. 48, p. 445.
  4. I have followed the account given by Professor J. Parsons Schaefier, Amer, Journ, Anat. 1916, vol. 20, p. 125.
  5. E. Zuckerkandl, Ergebnisse der Anat. 1908, vol. 18, p. 801.
  6. Ivar Broman, Jubilee Festschrift of the University of Lund, 1918.
  7. For references to Literature see Olof Carsall, Journ. Comp. Neur. 1918, vol. 30, p. 1 ; R. McCotter, ibid, 1913, vol, 23, p. 145 ; H. Ayrers, ibid^ 1919, vol. 30, p. 323,
  8. See references, p. 174.
  9. See Schaeffer, Amer, Jovrn. Anat. 1912, vol. 13, p. 1.


Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Human Embryology and Morphology: 1 Early Ovum and Embryo | 2 Connection between Foetus and Uterus | 3 Primitive Streak Notochord and Somites | 4 Age Changes | 5 Spinal Column and Back | 6 Body Segmentation | 7 Spinal Cord | 8 Mid- and Hind-Brains | 9 Fore-Brain | 10 Fore-Brain Cerebral Vesicles | 11 Cranium | 12 Face | 13 Teeth and Mastication | 14 Nasal and Olfactory | 15 Sense OF Sight | 16 Hearing | 17 Pharynx and Neck | 18 Tongue, Thyroid and Pharynx | 19 Organs of Digestion | 20 Circulatory System | 21 Circulatory System (continued) | 22 Respiratory System | 23 Urogenital System | 24 Urogenital System (Continued) | 25 Body Wall and Pelvic Floor | 26 Limb Buds | 27 Limbs | 28 Skin and Appendages | Figures