584 CLASS XVII. 



lymphatics run between its lamina, and the glands belonging to the 

 lymphatic system are situated there. The mammals are the only 

 vertebrate animals in which conglomerate or lymphatic glands are 

 met with in the mesentery. Commonly they are larger and less 

 numerous than in man, and often unite (in many carnivores) to form 

 a single mass, to which the name of Pancreas Asellii has been 

 given ^, in which case only a few small distinct glands occur in 

 addition. The chyle, conducted to the conglomerate glands by the 

 chyle vessels, is usually received by a single thoracic duct, which 

 opens into the left subclavian vein 2. Besides the glands in the 

 mesentery, conglomerate glands occur in other parts of the body in 

 greater number than in birds, and the lymphatics differ from those 

 of other vertebrate animals in having valves more numerous and 

 more perfect ^ 



The heart consists as in the birds of two ventricles and two auri- 

 cles, and is invested by the pericardium. The form of the heart is 

 various ; in the cetaceans it is broad, as also in the elephant, elon- 

 gate in the dog, but round in most monkeys, obtusely conical in 

 the horse, the ox, the orang outan and man. In man the heart is 

 placed obliquely, and rests by one of its surfaces on the diaphragm ; 

 such also is the case in the orang and the chimpansee. In the 

 rest of the mammals it is almost always placed more in a straight 

 line, and either does not reach the diaphragm at all, or, as in most 

 of the monkeys, with its apex alone*. In the septum of the auri- 

 cles is seen the oval fossa, the remains of the aperture which in the 

 foetus is found at this part and is named the foramen ovale. This 

 oval aperture is closed after birth, yet in the seals and other ani- 

 mals that live in water sometimes remains open. In the interior of 

 the right auricle under the oval fossa and near the mouth of the 

 inferior vena cava is seen the valve of Eustachius, which is wanting 



1 After the discoverer of the lymphatic sj^stem, Asellius, who first observed these 

 vessels in 1622 in the intestiocal canal of the dog. Be lactibm sive lacteis venis quarto 

 vasoruni nieseraicorum r/enere novo invento Gaspaki Asellii Dissertatio. Mediolani, 

 1627, 4to. 



2 If there be a left and a right thoracic duct, the last unites v^ith the first before the 

 passage into the venous system. 



3 Here also compare the Osservazioni of Panizza referred to above (p. 3.39). 



* The deep external separation of the venous and arterial halves of the heart in the 

 herbivorous Cetacea, especially in Halicore, the Dwjong, is remarkable. See figures in 

 Home, Lectures, iv. PI. l; Kapp Die Cetaceen, 1837, Taf. vill. (in a. foetus) &c. 



