uitGANS OF CIRCULATION. 4* 



ossification caller! the bone of the heart. The heart lies, for the 

 most part, in the median line, parallel with the sternum, rarely having 

 its apex, as in Man, directed to the left, though this is the case in the 

 Apes, the Sloth, and the Mole, and also in a less degree in some other 

 animals, as the Seal. 



The Aorta gives off first from its root the two coronary arteries, 

 rarely only a single one, as in the Elephant. The origin of the 

 vessels from the arch of the aorta exhibits, as is well known, fre- 

 quent varieties in Man, several of which occur as normal states in the 

 genera and orders of Mammalia. In the Horse and the Ruminan- 

 tia the aorta divides at once nt its origin into an anterior trunk, 

 or arteria innominata, which jrves T both carotid and subclavian 

 arteries, and a posterior trunk for tiie thoracic and abdominal aorta. 

 In most of the Carnivora, Rodentia, Marsupiata, and in the Hog, 

 Ant-eater and Pangolin, the left subclavian artery is distinct from the 

 innominata, and proceeds by itself from the arch. In the Dolphin 

 and Cheiroptera, at least in Vespertilio murinus, two arterise innomi- 

 nate arise, and give off each a carotid and subclavian upon either 

 side. The human arrangement, namely, with three main trunks, 

 of which the innominata gives off the right common carotid and 

 subclavian arteries, occurs partly in the Apes, Carnivora, some 

 Rodentia and most Edentata. It is very rarely, as in the Ele- 

 phant, that both the carotids are given off from a single common 

 trunk, situated in the middle between the two subclavian arteries. 

 Sometimes, as in some diving animals, as the Seals and Narwhal, 

 the aorta forms near to its exit from the heart a sac-like expan- 

 sion. The subdivisions of the arterial system exhibit a host 

 of minor differences, which can not be entered upon further here. 

 It is only worthy of remark, that in some animals, as the Sloth and 

 Loris, which are remarkable for the slowness of their movements, 

 that the arteries of the arm and leg divide at the commencement 

 of the extremities into several (3) main trunks, two of which rami- 

 fy again into a number of finer anastomosing filaments (retia mi- 

 rabilia), which wind around the middle branch. Large arterial retia 

 mirabilia occur within the skull of the Ruminantia, and are situated 

 within the cavernous sinus, and extend even to the vertebral artery. 

 The Cetacea have many arterial plexuses in different situations in 

 connexion with the intercostal and thoracic arteries in the cavity of 

 the thorax, and upon both sides of the vertebral column from the 

 psoas muscle to the neck. 



The Pulmonary artery, in its mode of origin and the number of its 



