hi the Foetus of Vertebrated Animals 319 



its right and left cavities are formed, takes place considerably 

 later than the production of the septum of the ventricles ; and 

 he, therefore, does not agree with Rolando, Prevost, and Du- 

 mas, in believing that the obstruction thus produced to the flow 

 of blood from the right to the left auricle is to be regarded as 

 the cause of the development of the right ventricle. 



During last spring I was enabled to investigate this sub- 

 ject more carefully than had previously been done, by means 

 of some very large goose's eggs, which, having been hatched 

 for the proper time, presented to me hearts of such a size 

 that their cavities could be distinguished with the naked eye 

 alone. The observations I then made confirmed in the more 

 important particulars the account which Baer gives of the se- 

 paration of the right from the left ventricle, by the formation 

 of a septum rising between them : they lead me to believe, 

 however, that this septum is not produced exactly in the man- 

 ner he has described. I can have no doubt, however, of the 

 existence of a gradually increasing septum in the hearts of 

 the foetus of all birds, as I have examined the foetus of 

 the common fowl, the turkey, the duck, and the goose, and 

 have found corresponding appearances in them all. According 

 to my observations, the septum does not rise from the apex of 

 the heart, but begins to be formed by imperceptible degrees 

 towards the right and upper side of the common ventricle (Fig. 

 19. C, D, z). At and before the time at which the first traces 

 of the interventricular septum appears, the internal paries of the 

 ventricle is of a very spongy structure, being composed of nu- 

 merous loose fleshy fibres, interwoven with one another. From 

 part of these netted fibres, some of which, in a more advanced 

 state, no doubt constitute the columnae cameas of the ventricle, 

 the septum which divides the cavity springs ; but, from the gra- 

 dual manner in which it takes its origin, it is difficult to assign 

 any very definite period for the commencement of the right ven- 

 tricle. On the fifth day, in the goose (a period corresponding 

 nearly to the 65th hour in the chick), the septum becomes 

 more distinct. The right ventricle (Fig. 19- s'), now also ap- 

 pears as a distinct cavity, occupying the dilated part at the root 

 of the bulb of the aorta, on the right side of the heart. 



The septum of the ventricles (s), does not appear to be form- 



