The elements of embryology. / By M. Foster ... and Francis M. Balfour.

  • Michael Foster
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The elements of embryology. / By M. Foster ... and Francis M. Balfour. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    v.] last two disappear in the chick without giving rise to any permanent • structures. The first visceral cleft remains permanently open, but is drawn out by the oTowth of surrounding parts into a long tube, subsequently divided into the -meatus auditorius and the Eustachian tube. The other visceral cleits are : obUttirated. 15. By the end of the second day three pairs of aortic i arches had been established in connection with the heart. \When the visceral folds and clefts are formed, a definite J arrangement between them and the aortic arches is always The same Head as shewn in Fig. 37, seen from the Feont. IThe neck has been cut across between the first and second visceral folds, the - incision being carried through the first visceral cleft. In the cut sm-face h are seen the sections of the hind brain Hb., and of blood-vessels c. I I F. The first visceral fold; between the ends of the fold is seen a section of the somatopleure at its extreme forvyard limit; in it lies the aorta a. Below the folds is the cavity of the throat al, and /. Fis placed in the first visceral cleft. I C.H. Cerebral hemispheres. N. Nasal pit. cJi.f. groove indicating the choroidal fissure. observed. The first visceral cleft runs between the first and (^second aortic arches. Consequently the first aortic arch runs in the first visceral fold and the second in the second. In :the same way, the second visceral cleft lies between the ^■second and third aortic arches, the third aortic arch running in the third visceral fold. Each aortic arch runs in the thickened mesoblast of the corresponding fold. Arrived at the upper surface of the alimentary canal, >^these arches unite at acute angles to form a common trunk, the idorsal aorta (Fig. .39 A, A. 0), which runs along the back imme- idiately under the notochord. The length of this common single (trunk is not great, as it soon divides into two main branches Fig. 38. I