88 APPENDIX. 



uf regular series. Tlte intestinal tube seems to be the viscus, which first presents a defihitfi 

 conformation. It is at first straight, and afterwards it curves forwards, and is embraced by 

 the umbilical chord : it thus forms an angle and descends into the abdominal cavity, which 

 is open at its anterior aspect, and apparently continuous with the short and imperfectly de- 

 veloped chord. This turn of the intestinal canal, and its retention in the chord, seems to 

 form the umbilical vesicle, and the subsequent strangulation of the intestine by the constric- 

 tion and elongation of the chord first gives rise to an insulated appearence of this vesicle sub- 

 sequently, to its entire disappearAce, and lastly, to the separation of the intestines; tlie 

 vermiform appendix remaining as a type of the original conformation. 



About the same time that the intestinal tube curves into the umbilical chord, the urina- 

 ry bladder seems to be also prolonged into the chord, between the chorion and amnion, 

 forming the allantois and urachus, the former of which disappears as the fa-tus is developed 

 and the chord lengthened, the urachus only remaining at the time of birth, showing the 

 nature and type of the original conformation and the communication formerly existing be- 

 tween the allantois and bladder. 



We have already said that all the phases, through which the human embryo passes until 

 its conformation is perfected, correspond with the different stages of permanent organiza- 

 tion which characterize the animal scale. Since these observations were made, we perceive 

 that a similar opinion has been lately entertained by J. F. Meckel, and adopted by M. Be- 

 clard, in his recent and excellent work on General Anatonvy. Many proofs may be addu- 

 ced in support of this doctrine: so evident indeed is the analogy that a very close parallel 

 may be drawn between the stages of development through which the human foetus passes, 

 and the degrees of animal organization. 



The human embryo is at first an imperfectly formed vesicle ; such are the polypi and 

 others of the Zoophytes. At a remoter period it consists of a small vermiform body 

 without a distinct head, ov limbs ; sftch are the Echinodermata, and the Annelides. At a 

 still later period its limbs ; are equally developed, and its tail is prominent: such are the 

 Quadrupeds. 



As respects the nervous system, the ganglial or vital nerves first appear with their gan- 

 glions : such is the nervous structure of the invertebrated animals. As the embryo advan- 

 ces, the ganglial nerves give rise to two thin strips of medullary matter in the situation of 

 the spinal canal, these increase, coalesce, form the spinal and cervical marrow, (medulla 

 oblongata) and the tubercles of the latter, whence are produced the brain and cerebellum; 

 we observe the same conformation in reptiles, fishes, &c. 



The human foetus is remarkable for the rapidity with which it runs through the early 

 grades of the scale of organization. It is this circumstance that renders the early changes 

 which it experiences so difficult to be recognised. 



II. Of the circulation of the Fcetus. There are abundant facts to prove that the circu- 

 lation of the foetus is independent of that of the mother; that the blood of the former flows 

 from the umbilical arteries into the vein of the same name, and not from the uterine arteries 

 into that vein; that the foetal blood is fabricated by the foetus itself, from the juices furnish- 

 ed by the mother to the placenta, and, consequently, that the foetus (toes not receive one 

 drop ready formed from this organ by the umbilical vein.* 



existence in the perfect animals^ especially in man, we are led to infer that this system 

 is not originally formed from the centre towards the circumference, but that the origin 

 of its ramifications commences in the mucous or cellular tissue, when the embryo is 

 yet but in an apparently homogenious state ; and that as the textures become, in the 

 process of foetal growth, more and more developed, so the globules composing the 

 nervous system, and chiefly those of the g'anglial System of nerves are arranged into 

 cords of communication, chiefly in the course of the vessels, for the purpose Of pre- 

 serving communication between the organs, and reinforcing each of the textures with 

 the influence which they generate in their perfect state of development. As the pro- 

 cess of foetal growth proceeds, the nervous ramifications advance towards centres, 

 which vary in their characters, according to the species of the animal ; in those which 

 are more perfect those centres are numerous, and almost each differs in a more or less 

 sensible manner from the other, both as to appearance and function. 



* D. F. Lavagna concludes that the menstrual blood differs from common blood, only 

 in containing no fibrin ; also, that the blood in the uiribilical arteries of the funis contains 

 scarcely any fibrin, whilst that in the umbilical vein forms a tenacious jelly; hence, he in- 

 fers, that the blood acquires fibrin in the ciculation in the placenta, which it parts with in 

 its passage through the foetus Annali di Medicina di Milwio, JVo. 17. 



