in the Foetus of Vertebrated Animals. SI 5 



the ventricle, and the tube of the heart has the appearance of 

 being coiled into a knot. The auricle, originally placed poste- 

 riorly, now lies between the ventricle and the body of tlie foetus, 

 (55th hour), and towards the 65th hour, is in a great part con- 

 cealed behind the ventricle and bulb of the aorta. 



Between the 60th and 70th liours, the convex part of the 

 ventricle, afterwards becoming the apex, projects farther from the 

 breast of the foetus than before, and its concave part (75th hour, ?/) 

 becomes less curved, so that the depth of the ventricle is in- 

 creased. The passage from the auricle to the ventricle, the 

 canalis auricularis of Haller, does not increase in the same ratio 

 as these cavities, so that it now appears proportionally smaller 

 than before. About the 60th hour, the texture of the auricle 

 differs considerably from that of the ventricle ; the auricle re- 

 mains, as at first, composed of a thin and membranous paries, 

 while the ventricle has now become stronger and thicker, and is 

 rendered rough by the deposition of muscular fibres. 



Before the 65th hour, the heart is quite single, consisting, 

 like that of the fish, of one auricle, one ventricle, and the bulb 

 of the aorta. Towards the 70th and 80lh hours, the cavities of 

 the heart begin to be divided for the formation of the right and 

 left auricles and ventricles. Most late observers seem to be 

 agreed with regard to the inode in which the division of the 

 auricular cavity takes place ; but that of the ventricle has been 

 described very differently by those authors who have recently 

 written on the subject. The earlier authors, such as Al- 

 drovandus, Colter, Fabricius, Vesling *, and even Harvey -f*, 

 seem to have been altogether ignorant of this change ; and 

 Malpighi | appears to have been the first who ascertained that 

 the cavities of the heart are originally single, and afterwards 

 become divided by septa. Malpighi has pointed out the time 

 at which the auricle becomes divided, but Haller § first traced 

 this division from its commencement ; and little new has since 

 been added to his observations. 



Towards the 75th hour, the auricle has become considerably 



" See the Anatome Animalium of Blasius. 



•f Anatomical Exercitations concerning Generation. London, 1653.' 

 + De Formatione PuUi in Ovo. 1672. 



§ Sur la Formation du Coeur dans le Poulet. Lausanne, 1758, and in liis 

 Opera Minora, vol. ii. 



x2 



