Book - Quain's Embryology 5 - Revision history

Z8600021 at 06:23, 23 Ocak 2014

2014-01-23T06:23:52Z

← Older revision		Revision as of 17:23, 23 Ocak 2014
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	1, 1, chorda dorsal is in its sheath, pointed at its ~~nipper~~ end ; 2, points by three lines to the original intervals of the primitive vertebrae ; 3, in a similar manner indicates the places of new division into permanent bodies of vertebrte ; c indicates the body of the first cervical vertebra ; in this and the next the primitive division has disappeared, as also in the two lowest represented, viz. , d and the one above ; in those intermediate the line of division is shown : 4, points in three places to the vertebral arches ; and 5, similarly to three commencing ganglia of the spinal nerves : the dotted segments outside these i^arts are the muscular plates.		1, 1, chorda dorsal is in its sheath, pointed at its upper end ; 2, points by three lines to the original intervals of the primitive vertebrae ; 3, in a similar manner indicates the places of new division into permanent bodies of vertebrte ; c indicates the body of the first cervical vertebra ; in this and the next the primitive division has disappeared, as also in the two lowest represented, viz. , d and the one above ; in those intermediate the line of division is shown : 4, points in three places to the vertebral arches ; and 5, similarly to three commencing ganglia of the spinal nerves : the dotted segments outside these i^arts are the muscular plates.


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	c. In the Limbs.		c. In the Limbs.

	The scapula and coracoid. The clavicle in part, and all the other bones of the ~~Tipper~~ limbs (excepting sesamoid).		The scapula and coracoid. The clavicle in part, and all the other bones of the upper limbs (excepting sesamoid).

	The ilium, ischium, and pubis, and all the other bones of the lower limbs, including the patella, but excepting sesamoid of toe.		The ilium, ischium, and pubis, and all the other bones of the lower limbs, including the patella, but excepting sesamoid of toe.

Z8600021 at 06:22, 23 Ocak 2014

2014-01-23T06:22:50Z

Show changes

Z8600021: /* Relations of Cranial Nerves */

2012-10-12T00:07:26Z

Relations of Cranial Nerves

← Older revision		Revision as of 11:07, 12 October 2012
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	The fourth arch, which has no special name, but might be called suhhyoid or cervical, does not seem to form the basis of any particular organ, but is situated exactly at that part of the body which becomes elongated as the neck, — a part which may be considered as absent in the foetus, and the formation of which by a simple process of elongation gives rise to some peculiar features in the anatomy of the parts composing it.		The fourth arch, which has no special name, but might be called suhhyoid or cervical, does not seem to form the basis of any particular organ, but is situated exactly at that part of the body which becomes elongated as the neck, — a part which may be considered as absent in the foetus, and the formation of which by a simple process of elongation gives rise to some peculiar features in the anatomy of the parts composing it.

	==Relations of Cranial Nerves==		===Relations of Cranial Nerves===

	The rudiments of four cranial nerves, besides the optic and auditory afterwards to be referred to, are found at a very early period in connection with the plates now under consideration, and the following is the relation in which, according to Parker, they stand to these plates in all vertebrate animals. These nerves are the fifth pair or trip-eminus, the facial, the glosso-pharyngeal, and the pneumo-gastric. The two first are situated iu front, and the two latter behind the auditory sac. These nerves all divide or fork above a visceral cleft, one division going to the posterior face of the arch in front of the cleft, the other to the anterior face of the arch behind it.		The rudiments of four cranial nerves, besides the optic and auditory afterwards to be referred to, are found at a very early period in connection with the plates now under consideration, and the following is the relation in which, according to Parker, they stand to these plates in all vertebrate animals. These nerves are the fifth pair or trip-eminus, the facial, the glosso-pharyngeal, and the pneumo-gastric. The two first are situated iu front, and the two latter behind the auditory sac. These nerves all divide or fork above a visceral cleft, one division going to the posterior face of the arch in front of the cleft, the other to the anterior face of the arch behind it.
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	The amnion has been removed ; Al, allantois ; Clf, cerebral hemispheres ; FS, thalamencephalon, with Pn, the pineal gland projecting from its summit; MB, midbrain ; Cb, cerebellum ; IV, V, fourth ventricle ; Z, lens ; chs, choroid slit ; C'en V, iiuditory vesicle ; sm, superior maxillary process ; IF, 2F, &c., first, second, third and. fourth visceral folds ; V, fifth nerve in two divisions, one to the eye, and the other to the first visceral arch ; VII, seventh nerve passing to the second visceral arch ; Gph, glosso-pharjmgeal nerve passing to the third visceral arch ; Pg, pneumo -gastric nerve passing to the fourth arch ; / V, investing mass ; ch, notochord ; Mt, the heart ; HIP, muscle plates ; W, wing ; HL, hind limb.		The amnion has been removed ; Al, allantois ; Clf, cerebral hemispheres ; FS, thalamencephalon, with Pn, the pineal gland projecting from its summit; MB, midbrain ; Cb, cerebellum ; IV, V, fourth ventricle ; Z, lens ; chs, choroid slit ; C'en V, iiuditory vesicle ; sm, superior maxillary process ; IF, 2F, &c., first, second, third and. fourth visceral folds ; V, fifth nerve in two divisions, one to the eye, and the other to the first visceral arch ; VII, seventh nerve passing to the second visceral arch ; Gph, glosso-pharjmgeal nerve passing to the third visceral arch ; Pg, pneumo -gastric nerve passing to the fourth arch ; / V, investing mass ; ch, notochord ; Mt, the heart ; HIP, muscle plates ; W, wing ; HL, hind limb.


	The orbito-nasal and the palatine divisions of the trigeminus belong to the trabecular arch, the former above, the latter below the optic nerve. Of the other division, one part (the superior maxillary nerve) follows the palato-pterygoid arch, the other (inferior maxillary nerve) accompanies the mandibular arch.		The orbito-nasal and the palatine divisions of the trigeminus belong to the trabecular arch, the former above, the latter below the optic nerve. Of the other division, one part (the superior maxillary nerve) follows the palato-pterygoid arch, the other (inferior maxillary nerve) accompanies the mandibular arch.


	The facial nerve (portio dura of seventh pair) divides above the tympano-eustachian passage, its anterior part (chorda tympani) going to the posterior side of the mandibular arch, and its posterior part (descending branch of facial) to the outer or anterior side of the hyoid arch.		The facial nerve (portio dura of seventh pair) divides above the tympano-eustachian passage, its anterior part (chorda tympani) going to the posterior side of the mandibular arch, and its posterior part (descending branch of facial) to the outer or anterior side of the hyoid arch.


	The glosso-pharyngeal nerve, by a similar division, goes by its inner or anterior branch (lingual) to the inner or posterior side of the hyoid arch, and by its other division (pharyngeal) to the front of the first branchial or thyro-hyoid arch.		The glosso-pharyngeal nerve, by a similar division, goes by its inner or anterior branch (lingual) to the inner or posterior side of the hyoid arch, and by its other division (pharyngeal) to the front of the first branchial or thyro-hyoid arch.

Z8600021: /* Subcranial, Facial, or Pharyngeal Plates or Arches */

2012-10-12T00:06:41Z

Subcranial, Facial, or Pharyngeal Plates or Arches

Z8600021: /* The Cranial Flexures */

2012-10-12T00:04:17Z

The Cranial Flexures

← Older revision		Revision as of 11:04, 12 October 2012
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	The squamo-zygomatic and tympanic are produced from membrane.		The squamo-zygomatic and tympanic are produced from membrane.

	==The Cranial Flexures==		===The Cranial Flexures===

	The earliest and the most important of the cranial flexures is that which takes place at the anterior extremity of the notochord and in the region of the mid-brain or middle encephalic vesicle. Here, as previously stated, the notochord extends into the substance of the basis of the cranium as it is prolonged forwards in the line of the vertebral bodies. At this place the medullary tube, and the substance forming the wall of the cranium especially, undergoes a sudden bending downwards and forwards, so as to cause the projection of the thickened cranial base in a marked manner upwards. This coincides with the place where the investing mass and the trabeculae meet, and where ~~inferior]?~~ the ~~})ituitary~~ body, and superiorly the ~~infnndibnlum~~ are afterwards formed. The investing mass of blastema, in which the anterior extremity of the notochord is enclosed, and the notochord itself, terminate here behind the pituitary fossa, or what afterwards becomes that part, in a place corresponding to the dorsum selliB of human anatomy. Above and behind this, the middle cerebral vesicle forms the most prominent part of the cranium, which remains a characteristic feature of this part of the embryo head for a ~~consideral^le~~ time. Another early flexure of the cranium accompanies the development of the cerebellum from the third primary vesicle, a cleft now appearing behind and below the rudimentary cerebellum, in the region of the fourth ventricle, and above the medulla oblongata, and this flexure is necessarily attended with a convexity forwards, or another flexure in the place of the pons Varolii.		The earliest and the most important of the cranial flexures is that which takes place at the anterior extremity of the notochord and in the region of the mid-brain or middle encephalic vesicle. Here, as previously stated, the notochord extends into the substance of the basis of the cranium as it is prolonged forwards in the line of the vertebral bodies. At this place the medullary tube, and the substance forming the wall of the cranium especially, undergoes a sudden bending downwards and forwards, so as to cause the projection of the thickened cranial base in a marked manner upwards. This coincides with the place where the investing mass and the trabeculae meet, and where inferiorly the pituitary body, and superiorly the infundibulum are afterwards formed. The investing mass of blastema, in which the anterior extremity of the notochord is enclosed, and the notochord itself, terminate here behind the pituitary fossa, or what afterwards becomes that part, in a place corresponding to the dorsum selliB of human anatomy. Above and behind this, the middle cerebral vesicle forms the most prominent part of the cranium, which remains a characteristic feature of this part of the embryo head for a considerable time. Another early flexure of the cranium accompanies the development of the cerebellum from the third primary vesicle, a cleft now appearing behind and below the rudimentary cerebellum, in the region of the fourth ventricle, and above the medulla oblongata, and this flexure is necessarily attended with a convexity forwards, or another flexure in the place of the pons Varolii.


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	2, vesicle of the third venti'icle ; 3, mid-hrain ; 4, cerebellum ; 5, medulla oblongata ; c7i, notochord passing up through the bodies of the vertebrae into the basis cranii and terminating in the head between the infundibulum and the sac o£ the hypophysis cerebri ; s, the vertebral spines ; n, the spinal cord ; p, the phannix ; 7i, the heart ; I, the liver ; ?', the stomach and intestine; cl, the cloaca ; r, the urinary bladder and pedicle of the allantois ; it, u', the umbilicus containing the vitellointestinal duct, urachus and vessels ; between i, and /, superiorly, the Wolffian body is shown.		2, vesicle of the third venti'icle ; 3, mid-hrain ; 4, cerebellum ; 5, medulla oblongata ; c7i, notochord passing up through the bodies of the vertebrae into the basis cranii and terminating in the head between the infundibulum and the sac o£ the hypophysis cerebri ; s, the vertebral spines ; n, the spinal cord ; p, the phannix ; 7i, the heart ; I, the liver ; ?', the stomach and intestine; cl, the cloaca ; r, the urinary bladder and pedicle of the allantois ; it, u', the umbilicus containing the vitellointestinal duct, urachus and vessels ; between i, and /, superiorly, the Wolffian body is shown.

	The great cranial flexure thus marks the division between the strictly basi-cranial, or occipito-sphenoidal, and the basi-facial, or sphenoethmoidal part, the chorda terminating between those two portions of the cranial base, with a conical and sharp point. Here the chorda is itself lient downwards and forwards, and terminates in a ~~s]3ot~~ which corresponds to the post-sphenoid body, or dorsum sellas. According to Mihalkovics, who has recently investigated the subject with care (see Archiv filr j\Iikroskop. Anat., vol. xi., 1875,) in connection with the formation of the pituitary gland in mammals and birds, the chorda tapers off to a fine point in front of this spot, but presents a slight swelling just at the place of the future occipitosphenoidal suture.
			The great cranial flexure thus marks the division between the strictly basi-cranial, or occipito-sphenoidal, and the basi-facial, or sphenoethmoidal part, the chorda terminating between those two portions of the cranial base, with a conical and sharp point. Here the chorda is itself lient downwards and forwards, and terminates in a spot which corresponds to the post-sphenoid body, or dorsum sellas. According to Mihalkovics, who has recently investigated the subject with care (see Archiv filr j\Iikroskop. Anat., vol. xi., 1875,) in connection with the formation of the pituitary gland in mammals and birds, the chorda tapers off to a fine point in front of this spot, but presents a slight swelling just at the place of the future occipitosphenoidal suture.


	The formation of the mouth, and its opening by the fauces into the pharyngeal or first part of the primitive alimentary canal, are phenomena of development intimately connected with the formation of the central part of the cranium and sella turcica, but they are also associated with the development of the face, which is next to be considered.		The formation of the mouth, and its opening by the fauces into the pharyngeal or first part of the primitive alimentary canal, are phenomena of development intimately connected with the formation of the central part of the cranium and sella turcica, but they are also associated with the development of the face, which is next to be considered.

	Formation of the ~~Moutli~~ and Hypophysis ~~cerebri. —~~ Along with the changes which accompany the formation of the principal cranial ~~flexui-e~~, is associated in a remarkable manner the origin of a body (the pituitary gland or hypophysis cerebri) the nature and uses of which in the adult are ~~entii'cly~~
			===Formation of the Mouth and Hypophysis Cerebri===

			Along with the changes which accompany the formation of the principal cranial flexure, is associated in a remarkable manner the origin of a body (the pituitary gland or hypophysis cerebri) the nature and uses of which in the adult are entirely imkno-mi, but the constancy of whose presence, and the imiformity of its connections in the whole series of vertebrate animals, points to some important morphological relation.



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	In A, the faucial opening is still closed ; in R, it is formed ; c. anterior cerebral vesicle ; mc, meso-cerebrum ; mo, medulla oblongata ; co, corneous layer ; to, medullary layer ; if, infundibuhim ; avi, amnion ; spe, spheno-ethmoidal, be, central (dorsum sellte), and spo, sj^heno-occipital parts of the basis cranii ; /;, heart ; /, anterior extremity of primitive alimentary canal and opening (later) of the fauces ; i, cephalic jrortion of primitive intestine ; tha, thalamus ; p', closed opening of the involuted part of the pituitary body (py) ; ch, notochord ; pk, pharynx.		In A, the faucial opening is still closed ; in R, it is formed ; c. anterior cerebral vesicle ; mc, meso-cerebrum ; mo, medulla oblongata ; co, corneous layer ; to, medullary layer ; if, infundibuhim ; avi, amnion ; spe, spheno-ethmoidal, be, central (dorsum sellte), and spo, sj^heno-occipital parts of the basis cranii ; /;, heart ; /, anterior extremity of primitive alimentary canal and opening (later) of the fauces ; i, cephalic jrortion of primitive intestine ; tha, thalamus ; p', closed opening of the involuted part of the pituitary body (py) ; ch, notochord ; pk, pharynx.

	~~imkno-mi, but the constancy of whose presence, and the imiformity of its connections in the whole series of vertebrate animals, points to some important morphological relation.~~

	The general nature of this body, in its joint connection with the infundibulum of the brain on the one hand, and a diverticulum of the alimentary canal on the other, was first pointed out by Eatlike (Miiller's Archiv, 1838. p. 482), although he afterwards abandoned the view there set forth. It was, however, fully confirmed by others ; and, among recent observers, we owe more especially to William Miiller an elaborate investigation of the whole subject (Jenaische Zeitschr., vol. vi., 1871), who traced most carefully the ~~nei-vous~~ and diverticular elements in their development, and their union with mesoblastic elements in the formation of the gland, Goette next ascertained that the diverticulum from below is connected with the buccal cavity and epiblast, and not with the pharynx and hypoblast, as was previously supposed (Archiv fur Miki-oscop. Anat., vol. ix., p. 397). The observations of Mihalkovics on Mammals complete the history of this point in development, and will be mahily employed in the following description.		The general nature of this body, in its joint connection with the infundibulum of the brain on the one hand, and a diverticulum of the alimentary canal on the other, was first pointed out by Eatlike (Miiller's Archiv, 1838. p. 482), although he afterwards abandoned the view there set forth. It was, however, fully confirmed by others ; and, among recent observers, we owe more especially to William Miiller an elaborate investigation of the whole subject (Jenaische Zeitschr., vol. vi., 1871), who traced most carefully the nervous and diverticular elements in their development, and their union with mesoblastic elements in the formation of the gland, Goette next ascertained that the diverticulum from below is connected with the buccal cavity and epiblast, and not with the pharynx and hypoblast, as was previously supposed (Archiv fur Miki-oscop. Anat., vol. ix., p. 397). The observations of Mihalkovics on Mammals complete the history of this point in development, and will be mahily employed in the following description.

	The formation of this body may be shortly described as consisting in the meeting and combination of two outgrowths from very different fundamental parts ; one cerebral or medullary from above, and the other corneous or epiblastic (glandular), from below, in a recess of the cranial basis which afterwards becomes the pituitary fossa (fig. 53.5, B, <f,'py). The cerebral outgrowth, the posteiior of the two parts, takes place by the fonnation of a pointed projection ~~do\\Tawards~~ of a portion of the lower medullaiy waU of the vesicle of the third ventricle, and its firm adhesion to the base of the cranium. This is the commencement of the infundibulum. Meanwhile, a little in front of the same place, there is projected upwards from below a part of the basilar surface of the cranium, so as to form a deep recess lined by the corneous layer from the back and upper part of the future mouth. This recess is the commencement of the hypophysis or pituitary- body in its glandular portion, which is not, as has been supposed, a recess from the pharynx, seeing that it is in front of the opening which is afterwards formed for the fauces. The depressed and sharpened out anterior part of the notochord is directed downwards and forwards, while the sac of the hypophysis is can-ied upwards and backwards, and, according to Mihalkovics, the attenuated end of the chorda soon disappears from between the infundibulum and the hypophysis, previous to the occurrence of the intimate union which follows between these two bodies. The anterior extremity of the chorda, therefore, is lost in the floor of the pituitary fossa, and the swollen or dilated portion of the chorda which succeeds, and which comes then to form the apparent termination, occupies the interval between the basi-occipital and the basi-sphenoidal cartilages. The chorda traced back from this point, presents another swelling at the junction of the basi-occipital cartilage with that of the odontoid process, into which last it passes. The third swelling of the chorda lies between the odontoid cartilage, and that of the body of the axis vertebra.
			The formation of this body may be shortly described as consisting in the meeting and combination of two outgrowths from very different fundamental parts ; one cerebral or medullary from above, and the other corneous or epiblastic (glandular), from below, in a recess of the cranial basis which afterwards becomes the pituitary fossa (fig. 53.5, B, <f,'py). The cerebral outgrowth, the posteiior of the two parts, takes place by the fonnation of a pointed projection downwards of a portion of the lower medullaiy waU of the vesicle of the third ventricle, and its firm adhesion to the base of the cranium. This is the commencement of the infundibulum. Meanwhile, a little in front of the same place, there is projected upwards from below a part of the basilar surface of the cranium, so as to form a deep recess lined by the corneous layer from the back and upper part of the future mouth. This recess is the commencement of the hypophysis or pituitary- body in its glandular portion, which is not, as has been supposed, a recess from the pharynx, seeing that it is in front of the opening which is afterwards formed for the fauces. The depressed and sharpened out anterior part of the notochord is directed downwards and forwards, while the sac of the hypophysis is can-ied upwards and backwards, and, according to Mihalkovics, the attenuated end of the chorda soon disappears from between the infundibulum and the hypophysis, previous to the occurrence of the intimate union which follows between these two bodies. The anterior extremity of the chorda, therefore, is lost in the floor of the pituitary fossa, and the swollen or dilated portion of the chorda which succeeds, and which comes then to form the apparent termination, occupies the interval between the basi-occipital and the basi-sphenoidal cartilages. The chorda traced back from this point, presents another swelling at the junction of the basi-occipital cartilage with that of the odontoid process, into which last it passes. The third swelling of the chorda lies between the odontoid cartilage, and that of the body of the axis vertebra.


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	Face of the from before		Face of the from before



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	The flask-like outgrowth of the buccal epiblast which gives rise to the hypophysis cerebri, is now gradually shut off from the corneous layer and cavity of the mouth, iirst by the constriction, and subsequently by the closure of its place of communication. There remains however, for a considerable time, a longish.		The flask-like outgrowth of the buccal epiblast which gives rise to the hypophysis cerebri, is now gradually shut off from the corneous layer and cavity of the mouth, iirst by the constriction, and subsequently by the closure of its place of communication. There remains however, for a considerable time, a longish thread of union between the two (fig. 535, C, 7/). The epithelium of the enclosed portion subsequently undergoes development into glandular coeca and cell-cords, and its internal cavity becomes gradually obliterated. This fonns the anterior part or lobe of the pituitary body. The posterior part owes its origin to the combination with mesoblastic tissue of a. widened extension of the infundibular process of the brain, which is thrust in between the sac of the pituitary body and the dorsum sella;. The nervous structure of this posterior lobe afterwards disappears in the higher animals, but in the lower it retains its place as a part of the brain.




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	Fig. 538. — Plan op the Skull, &c., of the same Ejibryo seen from below. Magnified ten diameters (from Parker).		Fig. 538. — Plan op the Skull, &c., of the same Ejibryo seen from below. Magnified ten diameters (from Parker).

	In this ~~a7id~~ the preceding figure the letters, where ~~j)resent~~, indicate the following parts : —		In this and the preceding figure the letters, where present, indicate the following parts : —

	c' to 0^ , the five primary divisions of the brain ; a, the eye ; n, the nose ; m, the mouth ; <?•, cartilage of the trabeculEe ; ctr, cornua trabecularum ; pn, prenasal cartilage ; 2}p[/> pterygo-palatine cartilage ; mn, the mandibular arch with Meckel's cartilage ; te, first visceral cleft which becomes the tympanoeustachian passage ; au, the auditory vesicle ; hi/, the cerato-hyoid arch ; Ir, the branchial bars and clefts, 1 to 4; tItJi, the thyro-hyoid ; py, the pituitary fossa ; ch, the notochord in the cranial basis, .surrounded by the investing mass (ii') ; vii, facial nerve ; ix, glosso-pharyngeal ; X, pneumog;istric ; xii, hypoglossal nerve.



	thread of union between the two (fig. 535, C, 7/). The epithelium of the enclosed portion subsequently undergoes development into glandular coeca and cell-cords, and its internal cavity becomes gradually obliterated. This fonns the anterior part or lobe of the pituitary body. The posterior part owes its origin to the combination with mesoblastic tissue of a. widened extension of the infundibular process of the brain, which is thrust in between the sac of the pituitary body and the dorsum sella;. The nervous structure of this posterior lobe afterwards disappears in the higher animals, but in the lower it retains its place as a part of the brain.

			c' to 0^ , the five primary divisions of the brain ; a, the eye ; n, the nose ; m, the mouth ; , cartilage of the trabeculae ; ctr, cornua trabecularum ; pn, prenasal cartilage ; 2 pterygo-palatine cartilage ; mn, the mandibular arch with Meckel's cartilage ; te, first visceral cleft which becomes the tympanoeustachian passage ; au, the auditory vesicle ; hi/, the cerato-hyoid arch ; Ir, the branchial bars and clefts, 1 to 4; tItJi, the thyro-hyoid ; py, the pituitary fossa ; ch, the notochord in the cranial basis, .surrounded by the investing mass (ii') ; vii, facial nerve ; ix, glosso-pharyngeal ; X, pneumog;istric ; xii, hypoglossal nerve.

	==Subcranial, Facial, or Pharyngeal Plates or Arches==		==Subcranial, Facial, or Pharyngeal Plates or Arches==

Z8600021: /* The Cranium */

2012-10-12T00:00:02Z

The Cranium

← Older revision		Revision as of 11:00, 12 October 2012
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	===The Cranium===		===The Cranium===

	The basal portion of the cranium consists primarily of two fundamental parts. Of these the ~~i^osterior~~ is distinguished by the presence of the prolongation of the notochord within it as far forward as the part of the skull which afterwards becomes the pituitary fossa. This portion, which may be named occipito-sphenoid, is originally formed by the undivided investing mass of Ratlike, which surrounds the anterior extremity of the notochord, and contains the matrix of the future basi-occipital and basi-sphenoid cartilages. By its later extension to the sides, it forms the matrix of the exoccipitals and the periotic mass of cartilage which surrounds the primary auditory vesicles. The main part extends forward below the posterior and middle primary encephalic vesicles, ending at the pituitary fossa.		The basal portion of the cranium consists primarily of two fundamental parts. Of these the posterior is distinguished by the presence of the prolongation of the notochord within it as far forward as the part of the skull which afterwards becomes the pituitary fossa. This portion, which may be named occipito-sphenoid, is originally formed by the undivided investing mass of Ratlike, which surrounds the anterior extremity of the notochord, and contains the matrix of the future basi-occipital and basi-sphenoid cartilages. By its later extension to the sides, it forms the matrix of the exoccipitals and the periotic mass of cartilage which surrounds the primary auditory vesicles. The main part extends forward below the posterior and middle primary encephalic vesicles, ending at the pituitary fossa.

	The anterior portion of the basis cranii may be called sphcno-ethmoid, as containing the matrix of the pre-sphenoid, and the ethmoid cartilages. It is mainly produced in connection with the trabeculae cranii, which contain between their separated limbs the pituitary fossa. This part of the cranial basis contains no prolongation of the noto		The anterior portion of the basis cranii may be called sphcno-ethmoid, as containing the matrix of the pre-sphenoid, and the ethmoid cartilages. It is mainly produced in connection with the trabeculae cranii, which contain between their separated limbs the pituitary fossa. This part of the cranial basis contains no prolongation of the noto

Z8600021: /* 1. The Cranium */

2012-10-11T23:59:44Z

1. The Cranium

← Older revision		Revision as of 10:59, 12 October 2012
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	In the progressive development of the head the principal changes by which its fundamental parts come into shape may be enumerated shortly as follows, viz., First, increase of deposit and textural differentiation of the mesoblastic substance for the formation of the cranial walls in their basilar, lateral, and upper portions ; second, the interpolation of the sense-capsules as connected with the formation of the rudiments of the nose, eye, and ear ; third, the development of the cerebral hemispheres and other parts of the brain from the three primary encephalic vesicles; fovrtli, the occurrence of the several cranial inflections ; and fifth, the new formation of outgrowths for the development of the parts of the face.		In the progressive development of the head the principal changes by which its fundamental parts come into shape may be enumerated shortly as follows, viz., First, increase of deposit and textural differentiation of the mesoblastic substance for the formation of the cranial walls in their basilar, lateral, and upper portions ; second, the interpolation of the sense-capsules as connected with the formation of the rudiments of the nose, eye, and ear ; third, the development of the cerebral hemispheres and other parts of the brain from the three primary encephalic vesicles; fovrtli, the occurrence of the several cranial inflections ; and fifth, the new formation of outgrowths for the development of the parts of the face.

	==1. The Cranium==		===The Cranium===

	The basal portion of the cranium consists primarily of two fundamental parts. Of these the i^osterior is distinguished by the presence of the prolongation of the notochord within it as far forward as the part of the skull which afterwards becomes the pituitary fossa. This portion, which may be named occipito-sphenoid, is originally formed by the undivided investing mass of Ratlike, which surrounds the anterior extremity of the notochord, and contains the matrix of the future basi-occipital and basi-sphenoid cartilages. By its later extension to the sides, it forms the matrix of the exoccipitals and the periotic mass of cartilage which surrounds the primary auditory vesicles. The main part extends forward below the posterior and middle primary encephalic vesicles, ending at the pituitary fossa.		The basal portion of the cranium consists primarily of two fundamental parts. Of these the i^osterior is distinguished by the presence of the prolongation of the notochord within it as far forward as the part of the skull which afterwards becomes the pituitary fossa. This portion, which may be named occipito-sphenoid, is originally formed by the undivided investing mass of Ratlike, which surrounds the anterior extremity of the notochord, and contains the matrix of the future basi-occipital and basi-sphenoid cartilages. By its later extension to the sides, it forms the matrix of the exoccipitals and the periotic mass of cartilage which surrounds the primary auditory vesicles. The main part extends forward below the posterior and middle primary encephalic vesicles, ending at the pituitary fossa.

Z8600021: /* Relation of Vertebral Rudiments to the Notochord */

2012-10-11T23:57:58Z

Relation of Vertebral Rudiments to the Notochord

← Older revision		Revision as of 10:57, 12 October 2012
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	==Vertebral Column and Trunk==		==Vertebral Column and Trunk==

	==Relation of Vertebral Rudiments to the Notochord==		===Relation of Vertebral Rudiments to the Notochord===

	It has already been shown (General Phenomena of Development, p. 692), that all the parts of the skeleton ow^e their primitive formative material to mesoblastic elements, and that the bodies and arches of the vertebras, and the adjacent part of the cranial walls are formed from continuous blastodermic substance lying below and around the primitive medullary canal. A part also of the basis of the cranium has this in common witli the vertebral axis, that its formative substance surrounds the notochord, extending forward from the column of the vertebral bodies into the occipito-sphenoid part of the cranial basis, which is there composed of the formative substance termed the invesiing mass of Ratlike.		It has already been shown (General Phenomena of Development, p. 692), that all the parts of the skeleton ow^e their primitive formative material to mesoblastic elements, and that the bodies and arches of the vertebras, and the adjacent part of the cranial walls are formed from continuous blastodermic substance lying below and around the primitive medullary canal. A part also of the basis of the cranium has this in common witli the vertebral axis, that its formative substance surrounds the notochord, extending forward from the column of the vertebral bodies into the occipito-sphenoid part of the cranial basis, which is there composed of the formative substance termed the invesiing mass of Ratlike.


	It is to be remembered, however, that closely as the formative tissue of the bone elements appear to surround the notochord, that structure does not itself, nor by its sheath, contribute to the formation of the vertebral or basi-cranial bones, but merely lies within them ; and the formative material, out of which the bones are produced, is derived from mesoblastic substance which passes inwards from the primordial vertebral plates, and envelopes the chorda external to its sheath. The formation of the notochord, therefore, precedes that of the formative bone-elements which afterwards envelope it, and the remains of the notochord, unaffected directly by any ossifying change, are found in the interior of the commencing bones, and may be traced even for a long time throughout the whole length of the column of the bodies of the vertebrre.		It is to be remembered, however, that closely as the formative tissue of the bone elements appear to surround the notochord, that structure does not itself, nor by its sheath, contribute to the formation of the vertebral or basi-cranial bones, but merely lies within them ; and the formative material, out of which the bones are produced, is derived from mesoblastic substance which passes inwards from the primordial vertebral plates, and envelopes the chorda external to its sheath. The formation of the notochord, therefore, precedes that of the formative bone-elements which afterwards envelope it, and the remains of the notochord, unaffected directly by any ossifying change, are found in the interior of the commencing bones, and may be traced even for a long time throughout the whole length of the column of the bodies of the vertebrre.

	This important fact was first demonstrated by H. Miiller, of Wm-tzbrn-g-, who showed fui-ther that the notochord did not pass through the anterior arch of the atlas, but was traceable directly from the body of the axis vertebra through its odontoid process, and thence into the basi- occipital and basi-sphenoid bones, reaching as far as the pituitary fossa. (Heinrich Miiller, " Ub. d. Vorkommen von Eesten des Chorda Dorsalis b. Menschen nach der Geburt," in " Zeitsch. fiir Rat. Med.," von Henle u. Pfeifer, 1858, b. ii. See also Gegenbaur, " Untersuch. ub. Vergleich. Anat. Das Kopfskelet der Selachier," Leipzig, 1872. W. Miiller, " Bau der Chorda dorsalis," in '■ Jenasch. Zeitsch." b. vi. E. Dursy, " Zur Entwick. des Kopfes," 1869, and Mihalkovics, '• On the Chorda and Pituitary Body," in "Archiv filr Miki-oscop. Anat.," b. xi., 1875.)

			This important fact was first demonstrated by H. Miiller, of Wm-tzbrn-g-, who showed fui-ther that the notochord did not pass through the anterior arch of the atlas, but was traceable directly from the body of the axis vertebra through its odontoid process, and thence into the basi- occipital and basi-sphenoid bones, reaching as far as the pituitary fossa. (Heinrich Miiller, " Ub. d. Vorkommen von Eesten des Chorda Dorsalis b. Menschen nach der Geburt," in " Zeitsch. fiir Rat. Med.," von Henle u. Pfeifer, 1858, b. ii. See also Gegenbaur, " Untersuch. ub. Vergleich. Anat. Das Kopfskelet der Selachier," Leipzig, 1872. W. Miiller, " Bau der Chorda dorsalis," in '■ Jenasch. Zeitsch." b. vi. E. Dursy, " Zur Entwick. des Kopfes," 1869, and Mihalkovics, On the Chorda and Pituitary Body," in "Archiv filr Miki-oscop. Anat.," b. xi., 1875.)

	It may be mentioned further, as the result of H. Miiller's observations, that though in general the chorda passes through the middle of the vertebral bodies, the position was found subject to variation in the caudal portion of the column, where it sometimes ~~pa,?sed~~ above, and at other times below, the ~~vei-tebral~~ bodies.
			It may be mentioned further, as the result of H. Miiller's observations, that though in general the chorda passes through the middle of the vertebral bodies, the position was found subject to variation in the caudal portion of the column, where it sometimes passed above, and at other times below, the vertebral bodies.


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	The interesting observations of Kowalevsky on the existence of a chorda dorsalis in Ascidia (Mem. de TAcad. de St. Petersboiu'g, torn. x. and xi., 1867 and 1868), would appear to show that this structure, and the type of development which accompanies it, are not confined to vertebrate animals, and that in them the notochord may present more of a merely vestigial character than constitute an important element in the formation of the skeleton. The constancy of its position and relations, however, is an important fact regai-ding its history.		The interesting observations of Kowalevsky on the existence of a chorda dorsalis in Ascidia (Mem. de TAcad. de St. Petersboiu'g, torn. x. and xi., 1867 and 1868), would appear to show that this structure, and the type of development which accompanies it, are not confined to vertebrate animals, and that in them the notochord may present more of a merely vestigial character than constitute an important element in the formation of the skeleton. The constancy of its position and relations, however, is an important fact regai-ding its history.


	The notochord does not undergo transverse segmentation in the same manner as the protovertebral plate does. It remains undivided to the last, but in the course of vertebral ossification it shows alternate diminutions and enlargements of its diameter, corresponding in number and position with the vertebral divisions. One of these enlargements is found between the odontoid process and the basi-occipital bone, and another has been observed by Mihalkovies in the interval betwecn the basi-occipital and the basi-sphenoid bones or their cartilagenous matrices.		The notochord does not undergo transverse segmentation in the same manner as the protovertebral plate does. It remains undivided to the last, but in the course of vertebral ossification it shows alternate diminutions and enlargements of its diameter, corresponding in number and position with the vertebral divisions. One of these enlargements is found between the odontoid process and the basi-occipital bone, and another has been observed by Mihalkovies in the interval betwecn the basi-occipital and the basi-sphenoid bones or their cartilagenous matrices.
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	1, 2, the three primary enceplialic vesicles ; in front and to the sides the cephalic fold ; crossing at 2 the fovea cardiaca ; 3, the caudal extremity of the medullary canal dilated into a rhomboid form ; 4, 4, six primordial vertebral divisions.		1, 2, the three primary enceplialic vesicles ; in front and to the sides the cephalic fold ; crossing at 2 the fovea cardiaca ; 3, the caudal extremity of the medullary canal dilated into a rhomboid form ; 4, 4, six primordial vertebral divisions.

	In front of this last swelling, the chorda is ~~beiit~~ down below the base of the skull, and tapering to a fine filament, ends or is lost in the floor of the pituitary fossa. The enlargements now mentioned have some interest in connection with the question of the vertebral constitution of the skull
			In front of this last swelling, the chorda is bent down below the base of the skull, and tapering to a fine filament, ends or is lost in the floor of the pituitary fossa. The enlargements now mentioned have some interest in connection with the question of the vertebral constitution of the skull in number and position to the vertebral segments of the body (somatomes of Goodsir) ; each one comprising superficially a segment of the muscular plate, and more deeply a pair of intervertebral ganglia and nerves, as well as the parts of the skeleton which lie before and behind them.

	===Segmentation of the Protovertebrae===		===Segmentation of the Protovertebrae===
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			The more obvious protovertebral segmentation docs not extend into the mesoblastic tissue beyond the commencement of the basis of the cranium, the mass of blastema which there surrounds the prolongation of the notochord (the investing mass of Rathke) remaining one and undivided, or being devoid at least of the marked cleavage which occurs in the strictly vertebral part.
	in number and position to the vertebral segments of the body (somatomes of Goodsir) ; each one comprising superficially a segment of the muscular plate, and more deeply a pair of intervertebral ganglia and nerves, as well as the parts of the skeleton which lie before and behind them.

	The more obvious protovertebral segmentation docs not extend into the mesoblastic tissue beyond the commencement of the basis of the cranium, the mass of blastema which there surrounds the prolongation of




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	B, transverse horizontal section through a part of one dorsal vertebra. 1, remains of the chorda dorsalis in the middle of the body ; 2, arch of the vertebra ; 3, head of a rib.		B, transverse horizontal section through a part of one dorsal vertebra. 1, remains of the chorda dorsalis in the middle of the body ; 2, arch of the vertebra ; 3, head of a rib.

	~~the notochord (the investing mass of Ratlike) remaining one and undivided, or being devoid at least of the marked cleavage which occurs in the strictly vertebral part.~~


	It is ~~fi'om~~ this protovertebral plate on each side, whether in its entire primitive condition, or in its later and divided state, that the material is derived for the formation of the bodies and laminae of the vertebra? and the muscles which cover them. This is effected by the rapid increase of the mesoblast, and by the extension of that structure beyond the immediate confines of the vertebral laminae in an inward and downward direction, so as to throw a quantity of new mesoblastic material round the notochord, and inwards and upwards, so as to pass in between the primary medullary canal and the enveloping layer of epiblast.
			It is from this protovertebral plate on each side, whether in its entire primitive condition, or in its later and divided state, that the material is derived for the formation of the bodies and laminae of the vertebra? and the muscles which cover them. This is effected by the rapid increase of the mesoblast, and by the extension of that structure beyond the immediate confines of the vertebral laminae in an inward and downward direction, so as to throw a quantity of new mesoblastic material round the notochord, and inwards and upwards, so as to pass in between the primary medullary canal and the enveloping layer of epiblast.

Z8600021: /* Segmentation of the Protovertebrae */

2012-10-11T23:55:51Z

Segmentation of the Protovertebrae

← Older revision		Revision as of 10:55, 12 October 2012
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	In front of this last swelling, the chorda is beiit down below the base of the skull, and tapering to a fine filament, ends or is lost in the floor of the pituitary fossa. The enlargements now mentioned have some interest in connection with the question of the vertebral constitution of the skull		In front of this last swelling, the chorda is beiit down below the base of the skull, and tapering to a fine filament, ends or is lost in the floor of the pituitary fossa. The enlargements now mentioned have some interest in connection with the question of the vertebral constitution of the skull

	==Segmentation of the Protovertebrae==		===Segmentation of the Protovertebrae===

	The transverse vertebrate segmentation which occurs in the primary vertebral plates affects only that part of these plates which is formed of mesoblast. It begins at a very early period, as already stated, even before the close of the primary medullary canal, in the form of one or two, or it may be three short transverse transparent lines which separate a corresponding number of dark or condensed quadrilateral masses of the primitive vertebral plates. These quadrilateral masses, the so-called primordial vertehrcc (Urwirbel of the Germans) (fig. 526, -4, 4), do not, however, correspond merely to the vertebrae of the skeleton, nor are they directly converted into theii- rudiments, but they are rather divisions equivalent		The transverse vertebrate segmentation which occurs in the primary vertebral plates affects only that part of these plates which is formed of mesoblast. It begins at a very early period, as already stated, even before the close of the primary medullary canal, in the form of one or two, or it may be three short transverse transparent lines which separate a corresponding number of dark or condensed quadrilateral masses of the primitive vertebral plates. These quadrilateral masses, the so-called primordial vertehrcc (Urwirbel of the Germans) (fig. 526, -4, 4), do not, however, correspond merely to the vertebrae of the skeleton, nor are they directly converted into theii- rudiments, but they are rather divisions equivalent

Z8600021: /* The muscular plate */

2012-10-11T23:55:36Z

The muscular plate

← Older revision		Revision as of 10:55, 12 October 2012
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	==The muscular plate==		===The muscular plate===

	Shortly after this extension of the mesoblast in the two directions before mentioned, another separation, or rather differentiation, is observed to take place in the direction of its length, in the formation along the dorsal surface, and below the epiblast, of a series of circumscribed plates which form the foundation of the erector muscles of the spine, and the great dorsal muscles of the trunk. These constitute together the muscular, or rather the musculo-cutaneous plate, for it appears also to include the formative rudiment of the true skin.		Shortly after this extension of the mesoblast in the two directions before mentioned, another separation, or rather differentiation, is observed to take place in the direction of its length, in the formation along the dorsal surface, and below the epiblast, of a series of circumscribed plates which form the foundation of the erector muscles of the spine, and the great dorsal muscles of the trunk. These constitute together the muscular, or rather the musculo-cutaneous plate, for it appears also to include the formative rudiment of the true skin.
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	There is thus deposited the formative material for the vertebral bodies, the vertebral arches, and the muscles which immediately surround them, together with the general integument.		There is thus deposited the formative material for the vertebral bodies, the vertebral arches, and the muscles which immediately surround them, together with the general integument.


	Meanwhile the vertebral segmentation goes on progressing from before backwards, extending through the dorsal, lumbar, sacral and coccygeal vertebrfB, till the process is complete ; but this is accompanied by other changes having reference to the separation of the nerveroots and ganglia from their formative tissue, and the development of the elements of the permanent vertebra?.		Meanwhile the vertebral segmentation goes on progressing from before backwards, extending through the dorsal, lumbar, sacral and coccygeal vertebrfB, till the process is complete ; but this is accompanied by other changes having reference to the separation of the nerveroots and ganglia from their formative tissue, and the development of the elements of the permanent vertebra?.


	In the outer portion of each protovertebral mass a transverse partition arises which separates the anterior part, as ganglion and nerve root, from the posterior, as matrix or forerunner of the bone and other structures which belong to the vertebral column. Each nerve then comes thus to be placed in front of the future permanent vertebra with the protovertebral division of which it was originally connected. In the inner or central part of the primordial vertebrae a different kind of change occurs, first, by the amalgamation or fusion of the protovertebral masses, and subsequently by their subdivision in such a manner that the intervertebral disc arises on a level with or opposite the centre of each protovertebral mass, and the blastema, out of which a permanent vertebral body is formed, is made up by the union of two parts, an anterior and a posterior, the first of these being derived from the hinder part of the preceding protovertebral mass of the same number, the other part being supplied by the anterior section of the protovertebral mass immediately following.		In the outer portion of each protovertebral mass a transverse partition arises which separates the anterior part, as ganglion and nerve root, from the posterior, as matrix or forerunner of the bone and other structures which belong to the vertebral column. Each nerve then comes thus to be placed in front of the future permanent vertebra with the protovertebral division of which it was originally connected. In the inner or central part of the primordial vertebrae a different kind of change occurs, first, by the amalgamation or fusion of the protovertebral masses, and subsequently by their subdivision in such a manner that the intervertebral disc arises on a level with or opposite the centre of each protovertebral mass, and the blastema, out of which a permanent vertebral body is formed, is made up by the union of two parts, an anterior and a posterior, the first of these being derived from the hinder part of the preceding protovertebral mass of the same number, the other part being supplied by the anterior section of the protovertebral mass immediately following.