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Human embryology and teratology
Book Reviews from the larger book. Some of these tables will be useful, for example, those giving dose regimens for antihypertensives or for urinary tract antiinfectives. It is difficult to imagine, however, that there will be a need for these tables beyond the student years: most practitioners become familiar with one or two regimens and use them for most patients, without needing to consult a pocket guide. The Quick Reference also offers the disadvantage of preserving in portable form the inaccuracies of the information about which I have already been critical. Finally, at the advertised price of $14.95 for the 57-page guide, it is likely that students will make their own crib sheets of necessary information for use in the small pocket looseleaf notebooks that are universal on medical school campuses. ANTHONY R. SCIALLI, MD
Reproductive Toxicology Center Washington, D.C.
Embryology a n d T e r a t o l o g y . O ' R a h i l l y R , Mtiller F. New York, Wiley-Liss; 1992. 317 pages. $159.95.
291
cause the bulbus cordis and ventricle grow faster than the other regions, the heart tube bends upon i t s e l f . . . As the primitive heart bends, the atrium and sinus venosus come to lie dorsal to the bulbus cordis, truncus arteriosus, and ventricle. Another area of disagreement with traditional teaching arises over the half-segment shift credited with formation of the vertebral bodies from adjacent sclerotome halves. The account in Langman's Medical Embryology (2) goes like this: During the 4th week of development, the cells of the sclerotomes shift their position to surround both the spinal cord and notocord • . . The thus-formed mesenchymal column retains traces of its segmental origin as the sclerotomic blocks are separated by less dense areas containing the intersegmental arteries. During further development, the caudal portion of each sclerotome segment proliferates extensively and condenses. This proliferation is so extensive that it proceeds into the subjacent intersegmental tissue and in this manner binds the caudal half of one sclerotome to the cephalic half of the subjacent sclerotome. Hence, by incorporation of the intersegmental tissue into the precartilaginous vertebral body, the body of the vertebra becomes intersegmental in origin.
Human
The Carnegie Collection is well known to anatomists as one of the earliest and most thoroughly studied repositories of human embryos in the world. The Collection was started in the early years of this century by Franklin Mall, a student of the embryologist Wilhelm His Sr (whose son was responsible for the bundle of His). Mall handed the collection down to George Streeter, who is best known for establishing the staging system for human embryos. This staging system was brought to its current form by Ronan O'Rahilly, the principal author of the newly issued
Human Embryology and Teratology. Advance advertisements for this book made much of the fact that human material was the basis for this new treatment of embryology. In fact, the authors preface their text with a restatement of the general aim of Franklin Mall's Manual of Human Embryology, to give "an account of the development of the human body, based throughout on human material." The implication is that embryologists who use nonhuman material and experiments may be misled in their attempts to understand human development. As a result, Doctors O'Rahilly and Miiller appear to have thrown their lot in with the reconstruction of embryologic events from the examination of different human specimens, frozen at one point in time. Perhaps because of this unique approach, Human Embryology and Teratology presents some material in an unconventional manner. Here for example is the account of the positioning of the atrial end of the heart: With the development of the head fold, a pocket of endoderm forms the foregut and the future cardiogenic plate is folded over beneath its floor, so that its cephalic and caudal ends become reversed. In this way, the future atrial end of the heart becomes situated more caudally, and the future ventricular end more cephalically. Here is the more traditional explanation, taken from Keith Moore's textbook (1): The arterial and venous ends of the heart tube are fixed by the branchial arches and the septum transversum, respectively. Be-
To this version, Doctors O'Rahilly and Muller respond: According to the concept of resegmentation.., the boundaries of the definitive vertebral bodies are determined by a vertical "shift" of half a segment in relation to the initial segmental limits. Although such an arrangement has frequently been assumed, the definitive appearance does not require i t . . . leaving the reader wondering how the myotomes come to bridge the intervertebral discs in the O'Rahilly-Miiller version. It should be clear that the examples of new versions of embryologic events are not meant as a detraction; the portrayal in Human Embryology and Tetratology may be correct and traditional views may require modification. The prospective reader of this book should understand, however, that there are several places herein where disagreements will arise. Of more importance, perhaps, are the characteristics of the explanations and illustrations used in this book. Although the authors purport to have written for beginners as well as for more advanced researchers, the text and accompanying artwork is not simple. In fact, I doubt a student could make use of this book without a solid grounding in anatomy and an introductory course in embryology. Missing, for example, are the fate maps of the pharyngeal clefts, arches, and pouches, replaced by a table telling the reader the anatomic names of the mature structures to which the embryonic structures give rise. The first arch, for example, is listed as giving rise to the tensor veli palatini, among other muscles. Although not incorrect, tabular presentation of this material does not make learning embryology particularly easy. The use of "Teratology" in the title signifies only that the embryologic basis of abnormal development is included in the discussion of normal development. This has become an integral part of modern embryology texts, and Human Embryology and Teratology adds nothing novel in this approach. There is, to be sure, a short introductory chapter titled "Teratology", but the attempt to present the basics of the field in l0 pages adds little to the book. The authors appear to be fascinated with innova-
292
Reproductive Toxicology
tions in reproductive medicine and molecular biology: no opportunity is missed to mention IVF and ultrasonography, but the information is superficial and detracts from the embryology. At times, there are embarassing errors as when homeoboxes are defined as " D N A sequences that encode amino acids." In general, however, this is a carefully constructed book by a prominent academic embryology team. It is difficult to recommend it to a particular readership group; however, I envision that embryologists and teratologists will want to take a look at a copy on approval. The approach put forward by Doctors O'Rahilly and Miiller is
Volume 7, Number 3, 1993 novel and may be of interest and importance to workers in this field. ANTHONY R. SCIALLI, MD
Reproductive Toxicology Center Washington, D.C. REFERENCES 1. Moore KL. The developing human. 3rd ed. Philadelphia: WB Saunders Company; 1982. 2. Sadler TW. Langman's medical embryology. 6th ed. Baltimore: Williams & Wilkins; 1990.
Reproductive Toxicology Center Washington, D.C.
Embryology a n d T e r a t o l o g y . O ' R a h i l l y R , Mtiller F. New York, Wiley-Liss; 1992. 317 pages. $159.95.
291
cause the bulbus cordis and ventricle grow faster than the other regions, the heart tube bends upon i t s e l f . . . As the primitive heart bends, the atrium and sinus venosus come to lie dorsal to the bulbus cordis, truncus arteriosus, and ventricle. Another area of disagreement with traditional teaching arises over the half-segment shift credited with formation of the vertebral bodies from adjacent sclerotome halves. The account in Langman's Medical Embryology (2) goes like this: During the 4th week of development, the cells of the sclerotomes shift their position to surround both the spinal cord and notocord • . . The thus-formed mesenchymal column retains traces of its segmental origin as the sclerotomic blocks are separated by less dense areas containing the intersegmental arteries. During further development, the caudal portion of each sclerotome segment proliferates extensively and condenses. This proliferation is so extensive that it proceeds into the subjacent intersegmental tissue and in this manner binds the caudal half of one sclerotome to the cephalic half of the subjacent sclerotome. Hence, by incorporation of the intersegmental tissue into the precartilaginous vertebral body, the body of the vertebra becomes intersegmental in origin.
Human
The Carnegie Collection is well known to anatomists as one of the earliest and most thoroughly studied repositories of human embryos in the world. The Collection was started in the early years of this century by Franklin Mall, a student of the embryologist Wilhelm His Sr (whose son was responsible for the bundle of His). Mall handed the collection down to George Streeter, who is best known for establishing the staging system for human embryos. This staging system was brought to its current form by Ronan O'Rahilly, the principal author of the newly issued
Human Embryology and Teratology. Advance advertisements for this book made much of the fact that human material was the basis for this new treatment of embryology. In fact, the authors preface their text with a restatement of the general aim of Franklin Mall's Manual of Human Embryology, to give "an account of the development of the human body, based throughout on human material." The implication is that embryologists who use nonhuman material and experiments may be misled in their attempts to understand human development. As a result, Doctors O'Rahilly and Miiller appear to have thrown their lot in with the reconstruction of embryologic events from the examination of different human specimens, frozen at one point in time. Perhaps because of this unique approach, Human Embryology and Teratology presents some material in an unconventional manner. Here for example is the account of the positioning of the atrial end of the heart: With the development of the head fold, a pocket of endoderm forms the foregut and the future cardiogenic plate is folded over beneath its floor, so that its cephalic and caudal ends become reversed. In this way, the future atrial end of the heart becomes situated more caudally, and the future ventricular end more cephalically. Here is the more traditional explanation, taken from Keith Moore's textbook (1): The arterial and venous ends of the heart tube are fixed by the branchial arches and the septum transversum, respectively. Be-
To this version, Doctors O'Rahilly and Muller respond: According to the concept of resegmentation.., the boundaries of the definitive vertebral bodies are determined by a vertical "shift" of half a segment in relation to the initial segmental limits. Although such an arrangement has frequently been assumed, the definitive appearance does not require i t . . . leaving the reader wondering how the myotomes come to bridge the intervertebral discs in the O'Rahilly-Miiller version. It should be clear that the examples of new versions of embryologic events are not meant as a detraction; the portrayal in Human Embryology and Tetratology may be correct and traditional views may require modification. The prospective reader of this book should understand, however, that there are several places herein where disagreements will arise. Of more importance, perhaps, are the characteristics of the explanations and illustrations used in this book. Although the authors purport to have written for beginners as well as for more advanced researchers, the text and accompanying artwork is not simple. In fact, I doubt a student could make use of this book without a solid grounding in anatomy and an introductory course in embryology. Missing, for example, are the fate maps of the pharyngeal clefts, arches, and pouches, replaced by a table telling the reader the anatomic names of the mature structures to which the embryonic structures give rise. The first arch, for example, is listed as giving rise to the tensor veli palatini, among other muscles. Although not incorrect, tabular presentation of this material does not make learning embryology particularly easy. The use of "Teratology" in the title signifies only that the embryologic basis of abnormal development is included in the discussion of normal development. This has become an integral part of modern embryology texts, and Human Embryology and Teratology adds nothing novel in this approach. There is, to be sure, a short introductory chapter titled "Teratology", but the attempt to present the basics of the field in l0 pages adds little to the book. The authors appear to be fascinated with innova-
292
Reproductive Toxicology
tions in reproductive medicine and molecular biology: no opportunity is missed to mention IVF and ultrasonography, but the information is superficial and detracts from the embryology. At times, there are embarassing errors as when homeoboxes are defined as " D N A sequences that encode amino acids." In general, however, this is a carefully constructed book by a prominent academic embryology team. It is difficult to recommend it to a particular readership group; however, I envision that embryologists and teratologists will want to take a look at a copy on approval. The approach put forward by Doctors O'Rahilly and Miiller is
Volume 7, Number 3, 1993 novel and may be of interest and importance to workers in this field. ANTHONY R. SCIALLI, MD
Reproductive Toxicology Center Washington, D.C. REFERENCES 1. Moore KL. The developing human. 3rd ed. Philadelphia: WB Saunders Company; 1982. 2. Sadler TW. Langman's medical embryology. 6th ed. Baltimore: Williams & Wilkins; 1990.