Z8600021 at 14:30, 25 Haziran 2015

2015-06-25T14:30:38Z

← Older revision		Revision as of 01:30, 26 Haziran 2015
Line 49:		Line 49:


	Reinak. ~~Tho~~ course of the bow, as compared with the transverse phiiie of tho body of the enibrj-o, in oblique, so that while the centre of the bow next the notochord is neai- the centre of the segment, the tips of the bow lie at the caudal limit of the segment and ultimately spparate the muscle plate of its own segment from that of the next following. The obliquity of the bow appears ti' me to be determined primarily by the arrangement of the spinal ganglia, the dorsal ends of which fill out the wi.dth of the segment, while the lower ]K>inted end is carrie<l forward to the anterior border of the segment; this disposition leaves the caudal side of the segment free for the mesenchyma and the differentiation of the vertebral bow; the obliquity is further assisted by the form of the muscle plate, as can be seen in Fig, -IVi. The [wrtiou of the bow imdemeath the chorda in the me<lian line is temted the hypoc'horda] brace (SiKiiige) and in its xdtimatc development differs considerably from the rest of the bow. The investing mass around the notiHrhord on the caudal side of the bow and above it becomes later the anl^e of the body of the vertebra. The vertebral bow may be Tegaraed as the primitive stage; it is found in the chick from the middle of the fourth to the middle of the fifth day; in cow embryos of 7-11 mm.		Reinak. The course of the bow, as compared with the transverse phiiie of tho body of the enibrj-o, in oblique, so that while the centre of the bow next the notochord is neai- the centre of the segment, the tips of the bow lie at the caudal limit of the segment and ultimately spparate the muscle plate of its own segment from that of the next following. The obliquity of the bow appears ti' me to be determined primarily by the arrangement of the spinal ganglia, the dorsal ends of which fill out the wi.dth of the segment, while the lower ]K>inted end is carrie<l forward to the anterior border of the segment; this disposition leaves the caudal side of the segment free for the mesenchyma and the differentiation of the vertebral bow; the obliquity is further assisted by the form of the muscle plate, as can be seen in Fig, -IVi. The [wrtiou of the bow imdemeath the chorda in the me<lian line is temted the hypoc'horda] brace (SiKiiige) and in its xdtimatc development differs considerably from the rest of the bow. The investing mass around the notiHrhord on the caudal side of the bow and above it becomes later the anl^e of the body of the vertebra. The vertebral bow may be Tegaraed as the primitive stage; it is found in the chick from the middle of the fourth to the middle of the fifth day; in cow embryos of 7-11 mm.

	The vertebral bow is destined to form the processes of the vertebra, and the manner in which its ends spread out against the muscle plate can be well seen in a cross-section, Fig. 244. At the time the bow is differentiated the muscle plate has become protuberant toward the notochord, and when the dense mesenchyma forming the bow spreads out it is forced by the muscle plate to grow dorsal ward, and ventral ward, and thereby to become, as it were, branched; the dorsal branch is the anlage of the neural arch; the ventral branch the anlage of the transverse or costal process, because it grows out still farther to form the anlage of the rib.		The vertebral bow is destined to form the processes of the vertebra, and the manner in which its ends spread out against the muscle plate can be well seen in a cross-section, Fig. 244. At the time the bow is differentiated the muscle plate has become protuberant toward the notochord, and when the dense mesenchyma forming the bow spreads out it is forced by the muscle plate to grow dorsal ward, and ventral ward, and thereby to become, as it were, branched; the dorsal branch is the anlage of the neural arch; the ventral branch the anlage of the transverse or costal process, because it grows out still farther to form the anlage of the rib.

	There follows a transitional state which is characterized by the gradual development of the c^irtilaginous vertebra. This stage extends in the chick fn)ra the middle of the fifth to the middle of the sixth day, and is found in cow embryos of 12-17 mm. The notochord exliibits signs of retrogi'ossive cliange, and is contracted at the level of the vertebral bow. The part of the investing mass (perichordal mesenchvma) iinniediatelv over the centre of the bow or hypochordal brace becomes the anlage of the interrertebral ligament, its cells Ix'coming first less crowded and then acquiring an elongated form; out of tliis anlage the adult ligament is slowly differentiated, chiefly by the development of connective-tissue fibrilIsB. The investing mass behind the hy]K)chordal brace develops into the cartilaginous l>ody of the vertebra, in the mammal before, in the bird after, cartilage begins to appear in the vertebral bow. In the mammals there are two centres of chondrification, which may be recognized in the bird also, although they are in the latter connected with one another under tiie chorda. The process of chondrification continues until out of the investing mass tho separate vertebral bod^" is differentiated. Moanwhih* the chondrification goes on in the vertebral bow, and in birds the whole 1k)W is converted into cartilage and unites with tho Ijody to form the completed vertebra. In mamm^ds except in the occipital and ant^M-ior cervical vertebne the central part does not form cartilage l)ut remains as a dense mesenchymal band, which can lie recognized as a more or less distinct structure for some time, but is ultimately lost in the substance of the intervertebral ligament. A median longitudinal section of a cow embryo a little more advanced. Fig. 245, shows the ])ersistence of the hyiK)chordal brace.

	~~The permanent stage~~ is ~~reacheil~~ by the ~~fusion~~ of the ~~cartilage of~~ the ~~bow with that~~ of the ~~body, which may be sfiid~~ to ~~l)e completed in the chi(k })v~~ the middle of the ~~seventh dav~~, and in cow ~~embrv'os~~ of ~~22 nun~~. In the ~~chick~~ the ~~whole~~ bow ~~is differentiated into cartilage, cUid its central~~ part ~~fuses with~~ the ~~vertebral lK~~)~~dy. In mammals this fusion does not take phice except in~~ the ~~occiput, but~~ the ~~two ends of each~~ bow ~~become cartilaginous and fuse with the corres\|K)nding vertebral lx)dy, except in~~ the ~~case~~ of the ~~first cervical vertebra~~, ~~see p. 430. The central portion of the bow in all vertebne below the~~ first ~~cervical disjippears~~ and ~~is lost in~~ the ~~intervertebral~~ ligament~~. lu a longitudinal section, Fig. 345, it can be seen that the tirst bow~~ is ~~a nell developed cartilaginoiiB piece~~, ~~Sc, while~~ the ~~second, is onlj partiall} chondnfied, while the third and fourth are almost lost m the intervertebral ligament~~. The ~~first bow, as just stated, forms~~ the ~~atlas During~~ the ~~de\ elopment~~ of ~~the cartilage~~ the vertebra ~~continues gronmg and~~ the ~~arches extend farther from the body; the neural arches gradually close over the medullary canal~~, ~~the closure taking place much earlier~~ in the ~~chick than~~ in the ~~mammal~~. In the ~~human embryo the neural arches extend at eight weeks only 11 short distance up the side~~ of ~~the spinal cord ; at three iin mths they have come~~ in ~~contact on~~ the ~~dor sal side in tUo dorsjd region~~, ~~but~~ are ~~still quite far apart iu~~ the ~~lumbar and sacral regions (Kiillikcr, " Gnindnsa," MH) and by the fourth month all the arches baveclused~~. The ~~development~~ of the ~~spinous pnMress needs to be further investigntod~~. ~~The ventral processes. Fig~~, ~~^44, spread downward~~ and ~~are brought, owing~~ to the ~~primitive inclination of thevfrt4'liral lx>w, totho caudal boundary~~- of the ~~segment to~~ which ~~they beloiif;~~, ~~and as they lie at~~ the ~~caudal edge~~ of the ~~muscle plate~~ of ~~their respective segments, they con- o'rui Wrv'icHi' v«tei]ni': c~~. ~~f,, b™ue» tribute to sepiirato that plate fr^.m the "} AJli'-AfSTtYSriiJ?!™"' "' ""^ next following~~. ~~These processes loose their continuity with the vertebra proper~~, ~~but remain connected with it by ligaments; they thus become~~ the ~~independent anlages~~ of the ~~ribs, where true ribs are developed~~.		There follows a transitional state which is characterized by the gradual development of the c^irtilaginous vertebra. This stage extends in the chick fn)ra the middle of the fifth to the middle of the sixth day, and is found in cow embryos of 12-17 mm. The notochord exliibits signs of retrogi'ossive cliange, and is contracted at the level of the vertebral bow. The part of the investing mass (perichordal mesenchvma) iinniediatelv over the centre of the bow or hypochordal brace becomes the anlage of the interrertebral ligament, its cells Ix'coming first less crowded and then acquiring an elongated form; out of tliis anlage the adult ligament is slowly differentiated, chiefly by the development of connective-tissue fibrilIsB. The investing mass behind the hy]K)chordal brace develops into the cartilaginous l>ody of the vertebra, in the mammal before, in the bird after, cartilage begins to appear in the vertebral bow. In the mammals there are two centres of chondrification, which may be recognized in the bird also, although they are in the latter connected with one another under tiie chorda. The process of chondrification continues until out of the investing mass tho separate vertebral bod^" is differentiated. Moanwhih* the chondrification goes on in the vertebral bow, and in birds the whole 1k)W is converted into cartilage and unites with tho Ijody to form the completed vertebra. In mamm^ds except in the occipital and ant^M-ior cervical vertebne the central part does not form cartilage l)ut remains as a dense mesenchymal band, which can lie recognized as a more or less distinct structure for some time, but is ultimately lost in the substance of the intervertebral ligament. A median longitudinal section of a cow embryo a little more advanced. Fig. 245, shows the persistence of the hypochordal brace.

			The permanent stage is reacheil by the fusion of the cartilage of the bow with that of the body, which may be sfiid to l)e completed in the chi(k })v the middle of the seventh dav, and in cow embrv'os of 22 nun. In the chick the whole bow is differentiated into cartilage, cUid its central part fuses with the vertebral lK)dy. In mammals this fusion does not take phice except in the occiput, but the two ends of each bow become cartilaginous and fuse with the corres\|K)nding vertebral lx)dy, except in the case of the first cervical vertebra, see p. 430. The central portion of the bow in all vertebne below the first cervical disjippears and is lost in the intervertebral ligament. lu a longitudinal section, Fig. 345, it can be seen that the tirst bow is a nell developed cartilaginoiiB piece, Sc, while the second, is onlj partiall} chondnfied, while the third and fourth are almost lost m the intervertebral ligament. The first bow, as just stated, forms the atlas During the de\ elopment of the cartilage the vertebra continues gronmg and the arches extend farther from the body; the neural arches gradually close over the medullary canal, the closure taking place much earlier in the chick than in the mammal. In the human embryo the neural arches extend at eight weeks only 11 short distance up the side of the spinal cord ; at three iin mths they have come in contact on the dor sal side in tUo dorsjd region, but are still quite far apart iu the lumbar and sacral regions (Kiillikcr, " Gnindnsa," MH) and by the fourth month all the arches baveclused. The development of the spinous pnMress needs to be further investigntod. The ventral processes. Fig, ^44, spread downward and are brought, owing to the primitive inclination of thevfrt4'liral lx>w, totho caudal boundary- of the segment to which they beloiif;, and as they lie at the caudal edge of the muscle plate of their respective segments, they con- o'rui Wrv'icHi' v«tei]ni': c. f,, b™ue» tribute to sepiirato that plate fr^.m the "} next following. These processes loose their continuity with the vertebra proper, but remain connected with it by ligaments; they thus become the independent anlages of the ribs, where true ribs are developed.

	Another point deserving attention is the relation of the vertebrffi to , the vertobnil arterv which arises, as described in Chapter XXIV., as a series of l<ingitudinal anastomoses between the intersegmental arteries; the vertebral artery begins to appear in (row embryos of 12 mm,, and is ii continuous stem in those of 15 mm. The vessel forming the nna.'^toniosis grows tlinaigh the mass of the vertebral bow during the transitional stage, while the inesenchyma is not very dense at the jioint \|»netratcd by the arter>\ This discoverj-, which we owe to Frorieji, sets aside the statement, which has l>ecome traditional, that the developing vertebra grows around the arterj", and shows instead that the artery grows thnmgh the developing anlagc of the vertebra. The artery, by its position, may te said to mark approximately the boundary between the neural and costal processes of the vertebra.

	The ~~ossijicaiion~~ of the vertebrce does not alter the morphology of the cartilaginous stage, and it is doubtful whether it is accompanied bj' any noteworthy change in the form of the single skeletal pieces. The ossification begins with two centres, one in each neural arch, and is continued by a third centre in the Ixxly of the vertebra. The centres in the neural arches lie near the body proper; that of the body appears in man about the seventh week. The centres of ossification of the l)ody become recognizable first in the dorsal region, and from there their differentiation progresses successively from vertebra to vertebra, lx)th heiidward and tailward. The centre is situated at first on the dorsal side of the chorda (Robin), but as the centre extends it incloses the notochord, which is gradually obliterated so that it can no longer lx> distinguislied aft(»r the actual formation of Ixme has commenced. The progress of ossification is very slow ; thus the preliminary degeneration covers the period, in cow embryos, in which their length increases from "2.2 to 0.0 cm., and it is not until the latter length has been atUiinod that the actual deposit of bone begins (Froriep, 86.1, 13(»). In man the centres do not attain the surface of the cartilage until the fourth or fifth month. Ultimately * the three deposits of bone fuse into a single osseous vertebra, but for a long ])eriod before this cartilage remains between the bony arches and the bony body, and on the dorsal side between the arches; these cartilaginous areas act as growing zones. The epiphyses are separate centres of ossification, whioli apjK^ar one on the cranial side, one on the caudal side of the body of each vertebra, but not until after birth. The development of tlio e])iphyses and their fusion with the main lx)dy have been investigatcKlby Schwegel, 58.1. To complete the adult bony vertebra there are five centres of ossification requisite.		Another point deserving attention is the relation of the vertebrffi to , the vertobnil arterv which arises, as described in Chapter XXIV., as a series of l<ingitudinal anastomoses between the intersegmental arteries; the vertebral artery begins to appear in (row embryos of 12 mm,, and is ii continuous stem in those of 15 mm. The vessel forming the nna.'^toniosis grows tlinaigh the mass of the vertebral bow during the transitional stage, while the inesenchyma is not very dense at the jioint \|»netratcd by the arter>\ This discovery, which we owe to Frorieji, sets aside the statement, which has l>ecome traditional, that the developing vertebra grows around the arterj", and shows instead that the artery grows thnmgh the developing anlagc of the vertebra. The artery, by its position, may te said to mark approximately the boundary between the neural and costal processes of the vertebra.


			The ossificaiion of the vertebrce does not alter the morphology of the cartilaginous stage, and it is doubtful whether it is accompanied bj' any noteworthy change in the form of the single skeletal pieces. The ossification begins with two centres, one in each neural arch, and is continued by a third centre in the Ixxly of the vertebra. The centres in the neural arches lie near the body proper; that of the body appears in man about the seventh week. The centres of ossification of the l)ody become recognizable first in the dorsal region, and from there their differentiation progresses successively from vertebra to vertebra, lx)th heiidward and tailward. The centre is situated at first on the dorsal side of the chorda (Robin), but as the centre extends it incloses the notochord, which is gradually obliterated so that it can no longer lx> distinguislied aft(»r the actual formation of Ixme has commenced. The progress of ossification is very slow ; thus the preliminary degeneration covers the period, in cow embryos, in which their length increases from "2.2 to 0.0 cm., and it is not until the latter length has been atUiinod that the actual deposit of bone begins (Froriep, 86.1, 13(»). In man the centres do not attain the surface of the cartilage until the fourth or fifth month. Ultimately * the three deposits of bone fuse into a single osseous vertebra, but for a long ])eriod before this cartilage remains between the bony arches and the bony body, and on the dorsal side between the arches; these cartilaginous areas act as growing zones. The epiphyses are separate centres of ossification, whioli apjK^ar one on the cranial side, one on the caudal side of the body of each vertebra, but not until after birth. The development of tlio e])iphyses and their fusion with the main lx)dy have been investigatcKlby Schwegel, 58.1. To complete the adult bony vertebra there are five centres of ossification requisite.


	Summary, — Every vertebra is developed within the limits of a single segment, that is, out of the mesenchyma produceil from the inner wall of a single segment. This point is es})ecially imjx)rtant because it is commonlv stated that each vertebra is derived from a^ljacent parts of two segments. Each vertebra has two distinct parts, -the vertebral how {Wirbelhotfen) and the vertebral lK>dy (Wirhefh'orper): both parts in their first stage consist of condenseil mesenchymal tissue. The bow appears first and is an arched band of tissue passing under the notochord, thence running obliquely backward and t(»rminating on the caudal side of the muscle plate of the segment. The lK)dy appears later in each segment just l)ehin(l the median part of the bow. The Ih)W and the Ix^dy l)otli cliondrify and fuse with one another, except in the first cervical s(»gm*^nt; in birds the whole l)ow becomes cartilaginous, but in mamniMls the middle part of the bow atrophies, except in the first cervical s(»gnient. The lateral portions of the bow form both the neural and costal arches; the distal		Summary, — Every vertebra is developed within the limits of a single segment, that is, out of the mesenchyma produceil from the inner wall of a single segment. This point is es})ecially imjx)rtant because it is commonlv stated that each vertebra is derived from a^ljacent parts of two segments. Each vertebra has two distinct parts, -the vertebral how {Wirbelhotfen) and the vertebral lK>dy (Wirhefh'orper): both parts in their first stage consist of condenseil mesenchymal tissue. The bow appears first and is an arched band of tissue passing under the notochord, thence running obliquely backward and t(»rminating on the caudal side of the muscle plate of the segment. The lK)dy appears later in each segment just l)ehin(l the median part of the bow. The Ih)W and the Ix^dy l)otli cliondrify and fuse with one another, except in the first cervical s(»gm*^nt; in birds the whole l)ow becomes cartilaginous, but in mamniMls the middle part of the bow atrophies, except in the first cervical s(»gnient. The lateral portions of the bow form both the neural and costal arches; the distal


	Eirts of the latter separate from the vertebra proper to form the anges of the ribs. The morphology of the vertebral column is completely determined while it is in the cartilaginous stage; ossification is merely a supplementary process and produces no important change in the form or anatomical relations of the vertebrae.		Eirts of the latter separate from the vertebra proper to form the anges of the ribs. The morphology of the vertebral column is completely determined while it is in the cartilaginous stage; ossification is merely a supplementary process and produces no important change in the form or anatomical relations of the vertebrae.

Z8600021: Created page with "{{Minot 1897 header}} {{Minot 1897 footer}}"

2014-03-29T06:56:04Z

Created page with "{{Minot 1897 header}} {{Minot 1897 footer}}"

New page

1897 Human Embryology 20 - Revision history

Z8600021 at 14:30, 25 Haziran 2015

Z8600021: /* Chapter XX. The Skeleton */

Z8600021 at 07:01, 31 March 2014

Z8600021 at 02:03, 30 March 2014

Z8600021: Created page with "{{Minot 1897 header}} {{Minot 1897 footer}}"