MAMMALS. 585 



in many mammals at the adult period. According to the investi- 

 gations of RUDOLPHI on the other hand, the projecting superior 

 margin of the fossa ovalis exists in many mammals in a highly 

 developed state, which is commonly named tuberculum Loweri 1 . 

 The right ventricle of the heart lies more forward in man than in 

 the rest of the mammals. In this chamber is seen the tricuspid 

 valve in place of the single, strong muscular valve of the birds ; in 

 the duck-mole, however, MECKEL found an arrangement similar in 

 form to that of birds. At the origin of the great artery there is 

 found in the deer and some other ruminants, as also in the hog, 

 one or two small bones in the septum of the ventricles, which are 

 cartilaginous in young animals. 



The mode is various in which the principal stems arise from 

 the arch of the great artery (aorta). This arch is always situated 

 on the left side, in order to pass into the descending aorta. But 

 before forming this arch, it gives off, close to its origin, two arteries 

 (or, according to CAMPER, in the elephant a single artery) for the 

 heart (arteria coronaria). From the arch itself there arise in man, 

 in many monkeys, in the mice and some other rodents, the seal, 

 the hedgehog, &c., three stems, on the right an arteria anonyma, 

 as a short common trunk of the right carotid and right subclavian 

 arteries, whilst on the left side each of these arteries arises by a 

 distinct stem. A more usual arrangement appears to be that where 

 there are only two stems; on the right side a short innominate 

 artery, which then divides into the two carotids and the right 

 subclavian, whilst the left subclavian, as the second stem, arises 

 separately from the arch. This is what is found in the Lemurids 

 and many monkeys, in most of the carnivores, many marsupiates 

 and rodents. In the ruminants and the horse, the aorta imme- 

 diately at its origin divides into an ascending branch, from which 

 the two subclavians and the two carotids arise, and a branch which 

 bends to the left downwards, the descending aorta. Other arrange- 

 ments, so that, for instance, there are two distinct subclavians and 

 a common stem for the two carotids, or two arterice anonymm, each 

 of which divides into a subclavian and a carotid, exist only in 



1 Grundriss der Physiol. 11. i, s. 331 333. Compare on the true nature of this 

 part and on the septum of the auricles, the remarks of RETZIUS, illustrated by beautiful 

 figures, in MUELLER'S Archiv, 1835, s. 161 170. 



