iu the Fd'tits of Vcrtehrated Animals. 321 



After the direct observation which has been made by Profes- 

 sor Baer and myself of the formation of the septum, the opinion 

 of Rolando, who denies that there can exist at any time a com, 

 munication between the ventricles, cannot, I apprehend, be re- 

 ceived as correct. Were farther proofs required of the accu- 

 racy of the statement given in this account, I think they are to 

 be found, 1^^, In the analogy which this mode of production 

 bears to that of the auricles ; 2^Z, In the similarity between these 

 chano-es in the bird and those observed in mammiferous animals ; 

 3d, In the existence of larger and smaller septa in the hearts of 

 many adult reptiles ; and, lastli/, By the satisfactory explanation 

 wiiich it affords of the communication which continues to exist 

 in many cases of malformation in the human as well as other 



species. 



After the sixth day, little farther change takes place in the 



heart of the chick. The apex of the ventricles becomes more 

 acute, and the parietes of the heart generally more muscular ; 

 but no alteration in its organization occurs till the approach of 

 the termination of foetal life, at which period the closure of the 

 foramen ovale, and the obliteration of the ductus arteriosi, fol- 

 low the inflation of the lungs by air. 



4. Development oftlie Heart in Mammalia. 



The heart of the dog, at the twenty- first day, represented by 

 Baer (Fig %. r s t), bears a great resemblance to that of the chick 

 at the 55th or 60th hour. At this lime, the heart of the dog 

 consists of a membranous tube, twisted on itself, and slightly 

 divided into an auricle, ventricle, and bulb of the aorta. It is 

 thus described by Baer * : " Denudata corporis parte curvata 

 optime in oculos cecidit cordis atrium (Fig. 8. r), venas reci- 

 piens, et ventriculus (* ), a sinistro ad dextrum latus in spiram 

 tortus et ita ac in pullis avium, deficiente pectore, a corporis la- 

 tei'ibus non tectum. In nostro fetu praeter cuticulam pectus te- 

 gentem jam tenerrimum pericardium adest, quod ante atrium 

 ct ventriculum distinguitur. Ex corde systema arteriosum 

 emergere vidi." 



Rathke f has described the heart of a pig at a period some- 

 what more advanced. In this animal he found the heart very 

 • In tlie EpLstola de Ovi, &c. p. 3. f Loc citat. 



