Human Embryology and Morphology 17 - Revision history

Z8600021: /* The Platysma and Muscles of the Face and Scalp */

2014-12-30T20:12:29Z

The Platysma and Muscles of the Face and Scalp

← Older revision		Revision as of 07:12, 31 December 2014
Line 182:		Line 182:
	==The Platysma and Muscles of the Face and Scalp==		==The Platysma and Muscles of the Face and Scalp==

	The platysma myoides, the muscles of the face, scalp and external ear, are derived from the muscle plate of the second or hyoid arch. They are supplied by the facial, the nerve of this arch. The muscle bud, from which the whole platysma sheet is developed, is still confined to the area of the hyoid arch until the 7th week of development when the bud spreads out and forms a continuous muscular hood over the head and neck. To this hood or sheet, which is composed of two layers, a deep and superficial, the name of platysma sheet may be given. It is developed in the superficial fascia. During its expansion or migration the platysma sheet separates into three main divisions — a part for the neck — platysma colli ; for the ear and occiput —the occipito-auricular ; and the facial division — for mouth, nose, orbits and forehead (Fig. 261). The muscles become differentiated during the 3rd month.		The platysma myoides<ref>R. Futamura, Anat. Hefte, 1907, vol. 32, p. 479 ; 1906, vol. 30, p. 433. </ref>, the muscles of the face, scalp and external ear, are derived from the muscle plate of the second or hyoid arch. They are supplied by the facial, the nerve of this arch. The muscle bud, from which the whole platysma sheet is developed, is still confined to the area of the hyoid arch until the 7th week of development when the bud spreads out and forms a continuous muscular hood over the head and neck. To this hood or sheet, which is composed of two layers, a deep and superficial, the name of platysma sheet may be given. It is developed in the superficial fascia. During its expansion or migration the platysma sheet separates into three main divisions — a part for the neck — platysma colli ; for the ear and occiput —the occipito-auricular ; and the facial division — for mouth, nose, orbits and forehead (Fig. 261). The muscles become differentiated during the 3rd month.

	~~2 R. Futamura, Anat. Hefte, 1907, vol. 32, p. 479 ; 1906, vol. 30, p. 433~~.

Z8600021: /* Muscles of the Visceral Arches */

2014-12-30T20:11:44Z

Muscles of the Visceral Arches

← Older revision		Revision as of 07:11, 31 December 2014
Line 173:		Line 173:
	==Muscles of the Visceral Arches==		==Muscles of the Visceral Arches==

	Within each visceral arch a muscle plate is formed — recalling in mode of appearance the muscle plates which develop in connection with each vertebral somite. The muscles arising in each arch are supplied by the nerve of that arch ; hence from the nerve supply alone one could infer the derivation of the musculature of the pharyngeal region. The muscles become differentiated in the latter part of the second month. All the muscles supplied by the facial nerve — the platysma, muscles of expression, the stapedius, stylo-hyoid, posterior belly of the digastric, etc. — are derived from the muscle plate of the 2nd or hyoid arch. The muscles of mastication, with the tensors of the palate and tympanum, the anterior belly of the digastric and mylohyoid, are derived from the muscle segment of the mandibular arch. The stylo pharyngeus is derived from the 3rd arch. The musculature of the soft palate and the constrictors of the pharynx are derived from the third and fourth arches. The musculature of the larynx comes from the fifth and sixth arches.		Within each visceral arch a muscle plate is formed<ref>F. H. Edgeworth, Journ. Anat. 1920, vol. 54, pp. 79, 124. </ref> — recalling in mode of appearance the muscle plates which develop in connection with each vertebral somite. The muscles arising in each arch are supplied by the nerve of that arch ; hence from the nerve supply alone one could infer the derivation of the musculature of the pharyngeal region. The muscles become differentiated in the latter part of the second month. All the muscles supplied by the facial nerve — the platysma, muscles of expression, the stapedius, stylo-hyoid, posterior belly of the digastric, etc. — are derived from the muscle plate of the 2nd or hyoid arch. The muscles of mastication, with the tensors of the palate and tympanum, the anterior belly of the digastric and mylohyoid, are derived from the muscle segment of the mandibular arch. The stylo pharyngeus is derived from the 3rd arch. The musculature of the soft palate and the constrictors of the pharynx are derived from the third and fourth arches. The musculature of the larynx comes from the fifth and sixth arches.

	<div id="Fig261"></div>		<div id="Fig261"></div>
	[[File:Keith1921 fig261.jpg\|600px\|alt=Fig. 261 ]]		[[File:Keith1921 fig261.jpg\|600px\|alt=Fig. 261 ]]

	'''Fig. 261.''' The expansion of the Platysma Sheet in a Human Foetus of 7 weeks. (Futamura.)		'''Fig. 261.''' The expansion of the Platysma Sheet in a Human Foetus of 7 weeks. (Futamura.)

	==The Platysma and Muscles of the Face and Scalp==		==The Platysma and Muscles of the Face and Scalp==

Z8600021: /* The Platysma and Muscles of the Face and Scalp */

2014-12-30T20:11:23Z

The Platysma and Muscles of the Face and Scalp

← Older revision		Revision as of 07:11, 31 December 2014
Line 183:		Line 183:

	The platysma myoides, the muscles of the face, scalp and external ear, are derived from the muscle plate of the second or hyoid arch. They are supplied by the facial, the nerve of this arch. The muscle bud, from which the whole platysma sheet is developed, is still confined to the area of the hyoid arch until the 7th week of development when the bud spreads out and forms a continuous muscular hood over the head and neck. To this hood or sheet, which is composed of two layers, a deep and superficial, the name of platysma sheet may be given. It is developed in the superficial fascia. During its expansion or migration the platysma sheet separates into three main divisions — a part for the neck — platysma colli ; for the ear and occiput —the occipito-auricular ; and the facial division — for mouth, nose, orbits and forehead (Fig. 261). The muscles become differentiated during the 3rd month.		The platysma myoides, the muscles of the face, scalp and external ear, are derived from the muscle plate of the second or hyoid arch. They are supplied by the facial, the nerve of this arch. The muscle bud, from which the whole platysma sheet is developed, is still confined to the area of the hyoid arch until the 7th week of development when the bud spreads out and forms a continuous muscular hood over the head and neck. To this hood or sheet, which is composed of two layers, a deep and superficial, the name of platysma sheet may be given. It is developed in the superficial fascia. During its expansion or migration the platysma sheet separates into three main divisions — a part for the neck — platysma colli ; for the ear and occiput —the occipito-auricular ; and the facial division — for mouth, nose, orbits and forehead (Fig. 261). The muscles become differentiated during the 3rd month.


	~~I F. H. Edgeworth, Journ. Anat. 1920, vol. 54, pp. 79, 124.~~

	2 R. Futamura, Anat. Hefte, 1907, vol. 32, p. 479 ; 1906, vol. 30, p. 433.		2 R. Futamura, Anat. Hefte, 1907, vol. 32, p. 479 ; 1906, vol. 30, p. 433.
Line 193:		Line 190:


	The muscles supplied by the facial nerve are peculiar in that they are the physical basis into which many mental states are reflected and in which they are realized. Through them mental conditions are manifested. It is found that the differentiation of this sheet into well-marked and separate muscles proceeds pari passu with the development of the brain. The more highly convoluted the brain of any primate, the more highly specialized are its facial muscles. It is remarkable that the sheet should arise from a visceral arch, which originally was closely connected with the function of respiration. To some extent the platysma does come into play during forced respiration even in man.		The muscles supplied by the facial nerve are peculiar in that they are the physical basis into which many mental states are reflected and in which they are realized. Through them mental conditions are manifested. It is found that the differentiation of this sheet into well-marked and separate muscles proceeds pari passu with the development of the brain. The more highly convoluted the brain of any primate, the more highly specialized are its facial muscles. It is remarkable that the sheet should arise from a visceral arch, which originally was closely connected with the function of respiration. To some extent the platysma does come into play during forced respiration even in man.


	==The Neck==		==The Neck==

Z8600021: /* Aortic Arch on the Right Side */

2014-12-30T20:10:58Z

Aortic Arch on the Right Side

← Older revision		Revision as of 07:10, 31 December 2014
Line 154:		Line 154:
	===Aortic Arch on the Right Side===		===Aortic Arch on the Right Side===

	In birds it is the 4th right arch which forms the aortic arch, and this occasionally happens in man. In amphibians both the right and left 4th arches persist. The two dorsal aortae in which they end, unite together, as they do in the human embryo, to form the descending thoracic aorta. The primitive subclavian arteries spring from the dorsal aortae above the point where these two vessels fuse together. In the latter part of the second month the short part of the right dorsal aorta, between the origin of the right siibclavian artery and point of aortic fusion, disappears, and then the subclavian artery appears as if it arose from the 4th right arch (Fig. 259). The communicating arterial twig, which is often seen uniting the superior intercostal artery of the right side with the artery of the lower spaces, is formed by a secondary anastomoses, and does not represent the right dorsal aorta. ^		In birds it is the 4th right arch which forms the aortic arch, and this occasionally happens in man. In amphibians both the right and left 4th arches persist. The two dorsal aortae in which they end, unite together, as they do in the human embryo, to form the descending thoracic aorta. The primitive subclavian arteries spring from the dorsal aortae above the point where these two vessels fuse together. In the latter part of the second month the short part of the right dorsal aorta, between the origin of the right siibclavian artery and point of aortic fusion, disappears, and then the subclavian artery appears as if it arose from the 4th right arch (Fig. 259). The communicating arterial twig, which is often seen uniting the superior intercostal artery of the right side with the artery of the lower spaces, is formed by a secondary anastomoses, and does not represent the right dorsal aorta.<ref>See E. Pearce Gould, Journ. Anat. and Physiol, 1909, vol. 43, p. 329.</ref>


	Not unfrequently the right subclavian arises, not from the innominate, which represents the right ventral aortic stem, but as the last of the great branches which arise from the arch of the aorta (Fig. 260). In such cases two things have happened : (1) the 4th right aortic arch has been .obliterated, (2) the right dorsal aorta has persisted.		Not unfrequently the right subclavian arises, not from the innominate, which represents the right ventral aortic stem, but as the last of the great branches which arise from the arch of the aorta (Fig. 260). In such cases two things have happened : (1) the 4th right aortic arch has been .obliterated, (2) the right dorsal aorta has persisted.

Z8600021: /* Dorsal Aortae */

2014-12-30T20:10:28Z

Dorsal Aortae

← Older revision		Revision as of 07:10, 31 December 2014
Line 167:		Line 167:
	[[File:Keith1921 fig260.jpg\|600px\|alt=Fig. 260 ]]		[[File:Keith1921 fig260.jpg\|600px\|alt=Fig. 260 ]]

	'''Fig. 260.''' Diagram showing tiie manner in which the Right Subclavian may arise as the last branch of the Arch of the Aorta. The parts of the aortic arch system which become obliterated are stippled.		'''Fig. 260.''' Diagram showing tiie manner in which the Right Subclavian may arise as the last branch of the Arch of the Aorta. The parts of the aortic arch system which become obliterated are stippled.


	~~1 See E. Pearce Gould, Journ. Anat. and Physiol, 1909, vol. 43, p. 329~~.

	==Muscles of the Visceral Arches==		==Muscles of the Visceral Arches==

Z8600021: /* Aortic Arches — the Arteries of the Visceral Arches */

2014-12-30T20:09:54Z

Aortic Arches — the Arteries of the Visceral Arches

← Older revision		Revision as of 07:09, 31 December 2014
Line 131:		Line 131:
	==Aortic Arches — the Arteries of the Visceral Arches==		==Aortic Arches — the Arteries of the Visceral Arches==

	In Fig. 248 is given the foetal arrangement of the aortic arches, and in Fig. 258 the vessels in the adult which are formed from them. The primitive aorta in the embryo divides into two trunks, which run forwards along the floor of the pharynx, one on each side, lying between the ventral ends of the visceral arches. These may be termed the right and left ventral aortic stems. From these stems arteries (aortic arches) pass upwards, one in each visceral arch, to terminate in the right and left dorsal aortae, which run backwards and become fused to form the descending thoracic aorta. The aortic arches are formed at a very early date. At the beginning of the 4th week the first or mandibular aortic arch is already present ; the second (liyoid), third, fourth, fifth and sixth appear in succession, but by the 6th week, when the 6th or pulmonary arch-^ has appeared, the first and second are in a process of atrophy. Only for a brief period towards the end of the 5th week, when the embryo is about 5 mm. long, are all the arches open, and even then the 1st is atrophic while the 6th or pulmonary is developing. The 5th arch has only a transient existence. The aortic arches are formed by the union of a network of blood spaces which are developed within each visceral arch.		In Fig. 248 is given the foetal arrangement of the aortic arches, and in Fig. 258 the vessels in the adult which are formed from them. The primitive aorta in the embryo divides into two trunks, which run forwards along the floor of the pharynx, one on each side, lying between the ventral ends of the visceral arches. These may be termed the right and left ventral aortic stems. From these stems arteries (aortic arches) pass upwards, one in each visceral arch, to terminate in the right and left dorsal aortae, which run backwards and become fused to form the descending thoracic aorta. The aortic arches are formed at a very early date. At the beginning of the 4th week the first or mandibular aortic arch is already present ; the second (liyoid), third, fourth, fifth and sixth appear in succession, but by the 6th week, when the 6th or pulmonary arch<ref>For literature on 6th arch and 5th cleft recess see Frank Reagan, Amer. Journ, Amt. 1911, vol. 12, p. 493 ; J. Tandler, Aiiat, Hefte, 1909, vol, 38, p. 393. </ref> has appeared, the first and second are in a process of atrophy. Only for a brief period towards the end of the 5th week, when the embryo is about 5 mm. long, are all the arches open, and even then the 1st is atrophic while the 6th or pulmonary is developing. The 5th arch has only a transient existence. The aortic arches are formed by the union of a network of blood spaces which are developed within each visceral arch.



	~~^ For literature on 6th arch and 5th cleft recess see Frank Reagan, Amer. Journ, Amt. 1911, vol. 12, p. 493 ; J. Tandler, Aiiat, Hefte, 1909, vol, 38, p. 393~~.


Line 162:		Line 158:


	Cases occur in which the permanent aorta is very much constricted at or near the point of entrance of the ductus arteriosus (see Fig. 259). It will be noticed that the corresponding part of the right dorsal aorta is obliterated. Such a constriction on the left side is to be regarded as corresponding to that on the right side, and indicates an attempt to produce a right aortic arch.		Cases occur in which the permanent aorta is very much constricted at or near the point of entrance of the ductus arteriosus (see Fig. 259). It will be noticed that the corresponding part of the right dorsal aorta is obliterated. Such a constriction on the left side is to be regarded as corresponding to that on the right side, and indicates an attempt to produce a right aortic arch.


	==Dorsal Aortae==		==Dorsal Aortae==

Z8600021: /* The Cartilages of the Arches */

2014-12-30T20:08:45Z

The Cartilages of the Arches

← Older revision		Revision as of 07:08, 31 December 2014
Line 90:		Line 90:
	==The Cartilages of the Arches==		==The Cartilages of the Arches==

	(Fig. 255).— The history of the skeletal basis of the first arch (Meckel's cartilage) has been already traced (p. 175). The cartilage of the 2nd or hyoid arch forms (Fig. 255) : (1) The tympano-hyal, embedded in the petro-mastoid, and originally continuous with the ear ossicles (Fig. 237). (2) The stylo-hyal, which ossifies in the early years of life and becomes joined to the tympano-hyal to form the styloid process. (3) The segment below, the epi-hyal, becomes ligamentous, and forms the stylo-hyoid ligament, but it also may become ossified. (4) The lowest segment, the cerato-hyal, forming the small horn of the hyoid. The epi-hyal lies behind and outside the tonsil, and when ossified has been excised under the belief that it was a foreign body. The body of the hyoid (basi-hyal) represents the fused ventral parts (copulae) of the 2nd and 3rd cartilages ; in the floor of the embryonic pharynx (Fig. 251) the ventral ends of the 2nd and 3rd arches end in a common or mesobranchial field. In this area the body of the hyoid develops. Prof. Parsons ^ has drawn attention to the fact that there is a ridge of bone on the upper surface of the body of the hyoid, which may occasionally form an almost separate bar. It lies between the lesser horns, and appears to represent the copula or body of the 2nd arch. It may be separated from the body of the hyoid by a foramen evidently for the passage of a remnant of the thyro-glossal duct. It will be seen later that the basal or pharyngeal part of the tongue arises from the floor of the pharynx in the field between the 2Dd and 3rd arches. The skeletal bases of their ventral parts come to form the bone of the tongue. The skeletal part of the hyoid arch suspends the tongue. There may be a process of bone from the concavity of the body representing the hyolingual of lower vertebrates (Parsons).		(Fig. 255).— The history of the skeletal basis of the first arch (Meckel's cartilage) has been already traced (p. 175). The cartilage of the 2nd or hyoid arch forms (Fig. 255) : (1) The tympano-hyal, embedded in the petro-mastoid, and originally continuous with the ear ossicles (Fig. 237). (2) The stylo-hyal, which ossifies in the early years of life and becomes joined to the tympano-hyal to form the styloid process. (3) The segment below, the epi-hyal, becomes ligamentous, and forms the stylo-hyoid ligament, but it also may become ossified. (4) The lowest segment, the cerato-hyal, forming the small horn of the hyoid. The epi-hyal lies behind and outside the tonsil, and when ossified has been excised under the belief that it was a foreign body. The body of the hyoid (basi-hyal) represents the fused ventral parts (copulae) of the 2nd and 3rd cartilages ; in the floor of the embryonic pharynx (Fig. 251) the ventral ends of the 2nd and 3rd arches end in a common or mesobranchial field. In this area the body of the hyoid develops.


			Prof. Parsons<ref>F. G. Parsons, Jouni. Anat. and Physiol. 1909, vol. 43, p. 279.</ref> has drawn attention to the fact that there is a ridge of bone on the upper surface of the body of the hyoid, which may occasionally form an almost separate bar. It lies between the lesser horns, and appears to represent the copula or body of the 2nd arch. It may be separated from the body of the hyoid by a foramen evidently for the passage of a remnant of the thyro-glossal duct. It will be seen later that the basal or pharyngeal part of the tongue arises from the floor of the pharynx in the field between the 2Dd and 3rd arches. The skeletal bases of their ventral parts come to form the bone of the tongue. The skeletal part of the hyoid arch suspends the tongue. There may be a process of bone from the concavity of the body representing the hyolingual of lower vertebrates (Parsons).

	<div id="Fig255"></div>		<div id="Fig255"></div>
Line 98:		Line 101:


	The great horn of the hyoid represents the cartilage of the 3rd arch (Fig. 255). In the lowest mammals the cartilaginous bases of the 4th and 5th arches unite to form the thyroid cartilage, but in higher mammals, including man, this cartilage is made up entirely by the 4th arch.^ The cartilages of the ultimate arches (5th and 6th) are probably represented by the cricoid, arytenoid and rings of the trachea (see also Fig. 375, p. 352).		The great horn of the hyoid represents the cartilage of the 3rd arch (Fig. 255). In the lowest mammals the cartilaginous bases of the 4th and 5th arches unite to form the thyroid cartilage, but in higher mammals, including man, this cartilage is made up entirely by the 4th arch.<ref>F. H. Edgeworth, Quart, Journ. Mic. Sc. 1916, vol. 61, p. 383. </ref> The cartilages of the ultimate arches (5th and 6th) are probably represented by the cricoid, arytenoid and rings of the trachea (see also Fig. 375, p. 352).

	~~1 F. G. Parsons, Jouni. Anat. and Physiol. 1909, vol. 43, p. 279.~~

	~~2 F. H. Edgeworth, Quart, Journ. Mic. Sc. 1916, vol. 61, p. 383.~~



	Even in mammals the cartilages of the three last branchial arches remain subservient to the purposes of respiration, just as in vertebrate animals in which these arches carry gills.		Even in mammals the cartilages of the three last branchial arches remain subservient to the purposes of respiration, just as in vertebrate animals in which these arches carry gills.

			==Nerves of the Visceral Arches==

			(see Figs. 256, 257, 93). — The 3rd division of the 5th nerve is, as has been already seen, the principal nerve of the first or mandibular arch. The nerve for the second or hyoid arch is represented by the 6th or facial. The nerve of the 3rd arch is the glossopharyngeal, that for the 4th is the superior laryngeal branch of the vagus, and for the 5th and 6th the inferior laryngeal (Fig. 257).
	~~Nerves of the Visceral Arches~~ (see Figs. 256, 257, 93). — The 3rd division of the 5th nerve is, as has been already seen, the principal nerve of the first or mandibular arch. The nerve for the second or hyoid arch is represented by the 6th or facial. The nerve of the 3rd arch is the glossopharyngeal, that for the 4th is the superior laryngeal branch of the vagus, and for the 5th and 6th the inferior laryngeal (Fig. 257).


Line 120:		Line 118:
	'''Fig. 256.''' The Visceral Arches and their Nerves and Ganglia in a Human Embryo of the 5th week. (Professor Streeter.)		'''Fig. 256.''' The Visceral Arches and their Nerves and Ganglia in a Human Embryo of the 5th week. (Professor Streeter.)

	The relationship of the nerves to the visceral arches is shown in Fig. 256, in a human embryo of five weeks. The position of these nerves in the adult is diagrammatically represented in Fig. 257. The Vth nerve and Gasserian ganglion are seen to lie at the base of the mandibular process. The ganglion of the Vllth and Vlllth nerves lies at the base of the hyoid (second) arch, in front of the otic vesicle, the fibres of the facial having already entered the arch. The glosso-pharyngeal and its ganglia lie behind the otic vesicle and at the base of fche third arch. The large ganglionic mass of the vagus lies over the bases of the fourth, fifth and sixth arches — or rather the tissue representing these arches. At this stage — the 5th week — ^the ganglion of the vagus and its issuing fibres rest on the dorsal wall of the pericardium, the heart being quite close to the source of its nerve fibres.		The relationship of the nerves to the visceral arches is shown in Fig. 256, in a human embryo of five weeks. The position of these nerves in the adult is diagrammatically represented in Fig. 257. The Vth nerve and Gasserian ganglion are seen to lie at the base of the mandibular process. The ganglion of the Vllth and Vlllth nerves lies at the base of the hyoid (second) arch, in front of the otic vesicle, the fibres of the facial having already entered the arch. The glosso-pharyngeal and its ganglia lie behind the otic vesicle and at the base of fche third arch. The large ganglionic mass of the vagus lies over the bases of the fourth, fifth and sixth arches — or rather the tissue representing these arches. At this stage — the 5th week — ^the ganglion of the vagus and its issuing fibres rest on the dorsal wall of the pericardium, the heart being quite close to the source of its nerve fibres.


	==Epibranchial Placodes==		==Epibranchial Placodes==

Z8600021: /* Formation of the Cervical Sinus */

2014-12-30T20:06:46Z

Formation of the Cervical Sinus

← Older revision		Revision as of 07:06, 31 December 2014
Line 66:		Line 66:
	'''Fig. 252.''' The Lining Membrane of the Pliarynx of a Human Embryo at the end of the 6th week of development (10 mm.) viewed on its ventral aspect. (Grosser.)		'''Fig. 252.''' The Lining Membrane of the Pliarynx of a Human Embryo at the end of the 6th week of development (10 mm.) viewed on its ventral aspect. (Grosser.)

	Although the cervical sinus usually disappears, it may remain and form a cyst in the neck, which opens on the anterior border of the sterno-mastoid a short distance above the sterno-clavicular joint. It may be drawn out into a trumpet-shaped tube, which ends in contact with the tonsillar recess, passing between the internal and external carotid arteries or in contact with the pharynx behind the hyoid (Fig. 253), connections which are explained by the origin of the sinus (Fig. 252). Often the cutaneous orifice is marked by a tag of skin representing a rudimentary external ear, which encloses a piece of cartilage.^ If the outer cleft depression in front of or behind the third arch persist, it must open in the cervical sinus.		Although the cervical sinus usually disappears, it may remain and form a cyst in the neck, which opens on the anterior border of the sterno-mastoid a short distance above the sterno-clavicular joint. It may be drawn out into a trumpet-shaped tube, which ends in contact with the tonsillar recess, passing between the internal and external carotid arteries or in contact with the pharynx behind the hyoid (Fig. 253), connections which are explained by the origin of the sinus (Fig. 252). Often the cutaneous orifice is marked by a tag of skin representing a rudimentary external ear, which encloses a piece of cartilage.<ref>For an account of the various developmental anomalies of the pharyngeal region see Keith, Brit. Med. Journ. 1909, Aug. 7th, 14th, 21st. For a description of its development see J. Ernest Frazer, Journ. Anat. and Physiol. 1910, vol. 44, p. 156 ; H. Fox, Amer. Jo^irn. Anat. 1908, vol. 8, p. 187 ; B. Kingsbury, Amer, .Journ. A7iat. 1915, vol, 18, p. 329. </ref> If the outer cleft depression in front of or behind the third arch persist, it must open in the cervical sinus.

	<div id="Fig253"></div>		<div id="Fig253"></div>
	[[File:Keith1921 fig253.jpg\|600px\|alt=Fig. 253 ]]		[[File:Keith1921 fig253.jpg\|600px\|alt=Fig. 253 ]]

	'''Fig. 253.''' Diagram to illustrate the various parts of the Visceral Clefts which may persist. The 2n(i inner cleft recess gives rise to the tonsil ; the recess may be in contact with an epithelial tube derived from the cervical sinus. The 3rd inner recess gives rise to the thymus and carotid bodies.		'''Fig. 253.''' Diagram to illustrate the various parts of the Visceral Clefts which may persist. The 2n(i inner cleft recess gives rise to the tonsil ; the recess may be in contact with an epithelial tube derived from the cervical sinus. The 3rd inner recess gives rise to the thymus and carotid bodies.

	==What becomes of the Visceral Clefts==		==What becomes of the Visceral Clefts==

Z8600021: /* What becomes of the Visceral Clefts */

2014-12-30T20:06:20Z

What becomes of the Visceral Clefts

← Older revision		Revision as of 07:06, 31 December 2014
Line 73:		Line 73:
	'''Fig. 253.''' Diagram to illustrate the various parts of the Visceral Clefts which may persist. The 2n(i inner cleft recess gives rise to the tonsil ; the recess may be in contact with an epithelial tube derived from the cervical sinus. The 3rd inner recess gives rise to the thymus and carotid bodies.		'''Fig. 253.''' Diagram to illustrate the various parts of the Visceral Clefts which may persist. The 2n(i inner cleft recess gives rise to the tonsil ; the recess may be in contact with an epithelial tube derived from the cervical sinus. The 3rd inner recess gives rise to the thymus and carotid bodies.

	===What becomes of the Visceral Clefts===		==What becomes of the Visceral Clefts==

	By the end of the second month the clefts, or, to be more exact, the representatives of clefts in the human embryo, have disappeared, except the upper part of the first. From the external depression of this part a soKd ingrowth of epithelium takes place which, ultimately becoming canaliculized, forms the external auditory meatus (Fig. 230). In connection with the upper or dorsal parts of the first and second cleft depressions the Eustachian tube and tympanum are formed, the membrana tympani remaining approximately in the position of a cleft membrane (p. 232).		By the end of the second month the clefts, or, to be more exact, the representatives of clefts in the human embryo, have disappeared, except the upper part of the first. From the external depression of this part a soKd ingrowth of epithelium takes place which, ultimately becoming canaliculized, forms the external auditory meatus (Fig. 230). In connection with the upper or dorsal parts of the first and second cleft depressions the Eustachian tube and tympanum are formed, the membrana tympani remaining approximately in the position of a cleft membrane (p. 232).



	^ For an account of the various developmental anomalies of the pharjTigeal region see Keith, Brit. Med. Journ. 1909, Aug. 7th, 14th, 21st. For a description of its development see J. Ernest Frazer, Journ. Anat. and Physiol. 1910, vol. 44, p. 156 ; H. Fox, Amer. Jo^irn. Anat. 1908, vol. 8, p. 187 ; B. Kingsbury, Amer, .Journ. A7iat. 1915, vol, 18, p. 329.




Line 93:		Line 87:

	'''Fig. 254.''' Showing the position of the External Cleft Depressions in the Adult. (For explanation, see text.)		'''Fig. 254.''' Showing the position of the External Cleft Depressions in the Adult. (For explanation, see text.)


	==The Cartilages of the Arches==		==The Cartilages of the Arches==

Z8600021 at 20:04, 30 December 2014

2014-12-30T20:04:53Z

← Older revision		Revision as of 07:04, 31 December 2014
Line 222:		Line 222:

	{{Keith1921 footer}}		{{Keith1921 footer}}

			[[Category:Head]]