14 



lar membrane, having a number of coils on their surface, not unaptly 

 to be compared, when magnified, to the convolutions of the small in- 

 testines. If all the fluid yolk be removed by gentle and repeated 

 washing, and the vitelline sac be successfully injected, we neverthe- 

 less do not observe any very remarkable vascularity. Large yellow 

 trunks appear dividing into small branches at the base of the folds, 

 and seem to contain the yellow globules of the yolk, but the red color 

 of the injection is only here and there apparent. These vessels are 

 the so-called vasa lutea of Haller ; but it is certain, I believe, from 

 r these injections, that the vessels do not contain the yellow corpuscules, 

 but that these yolk-globules are super-imposed and external to their 

 parietes. 



This fact seems to have struck Burdach and Von Baer, from whose 

 researches Burdach appears chiefly to have compiled his account. 



This author, describing the vessels of the vitelline sac at the 8th, 

 9th and 10th days, says "they are covered with a thick layer of cellu- 

 lar tissue containing the yellow vitelline globules which color it. Also 

 the small branches, which contain little blood (vasa lutea of Haller), 

 appear themselves yellow. But it appears to me doubtful whether 

 they admit the vitelline matter without change. It is perhaps only 

 the liquid part of the yolk that is absorbed by the veins, for at the close 

 of the 1 0th day its diminution (the contents of the yolk-sac) is more 

 considerable than could result from the passage of this substance 

 through the vitelline canal, and the blood is so little colored in the 

 small venous branches, that we recognise its mixture with water very 

 slightly coloured."* 



When, however, by repeated ablutions, and by directing a stream of 

 water over these folds, we detach the granular matter completely, we 

 behold an exquisite vascular structure that has few parallels for beau- 

 ty in the animal economy. We then see that vessels alone constitute 

 the framework of the undulating folds, the large trunks of which form 

 the base, while innumerable lesser branches dip deeper into the interior 

 of the sac, inosculating repeatedly, and terminating in a series of very 

 tortuous branches that fringe the extreme edge of each plica. Nu- 

 merous simple loops are observed, shooting from the sides of the lar- 

 ger trunks, and constituting the simplest type of vascular papilla; or 

 villosities of mucous surfaces. 



If then we conceive each trunk, anastomotic branch, in fact every 

 single loop and vessel, thickly covered with an aggregated arrangement 



♦Burdach, Physiologie, vol. iii. 



