2 PROFESSOR OWEN ON THE CHARACTERS, ETC. 



Mammals, like Birds, have a heart composed of two ventricles 

 and two auricles, and have warm blood : they breathe quickly ; but 

 inspiration is performed chiefly by the agency of the diaphragm ; 

 and the inspired air acts only on the capillaries of the pulmonary 

 circidation. 



The blood-discs are smaller than in Reptiles, and, save in the 

 Camel-tribe, are circular. The right auriculo-ventricular valve is 

 membranous, at least never entirely fleshy ; and the aorta bends 

 over the left, never over the right, bronchial tube. The primary 

 branches of the aorta are given off not immediately after, but at a 

 little distance from, its origin, and there is less constancy in the 

 order of their origin than in Birds : the phrenic arteries, the coeliac 

 axis, and the superior mesenteric artery are always branches of 

 the abdominal aorta, which terminates by dividing beyond the 

 kidneys into the iliac arteries, from which spring both the femoral 

 and ischiadic branches : the caudal or sacro-median artery, which 

 in some long-tailed Mammals assumes the character of the con- 

 tinued trunk of the aorta, never distributes arteries to the kidneys 

 or the legs, as in Birds. The kidneys are nourished, and derive 

 the material of their secretion, exclusively from the arterial system. 

 Their veins are simple, commencing by minute capillaries in the 

 parenchyma and terminating generally by a single trunk on each 

 side in the abdominal vena cava : they never anastomose with the 

 mesenteric veins. 



The kidneys are relatively smaller and present a more compact 

 figure than in the other vertebrate classes ; their parenchyma is 

 divided into a cortical and medullary portion, and the secreting 

 tubuli terminate in a dilatation of the excretory duct, called the 

 pelvis. 



The liver is generally divided into a greater number of lobes 

 than in Birds. The portal system is formed by veins derived 

 exclusively from the spleen and chylopoietic viscera. The cystic 

 duct, when it exists, always joins the hepatic, and does not enter 

 the duodenum separately. The pancreatic duct is commonly 

 single. 



The mouth is closed by soft flexible muscular lips : the upper 

 jaw is composed of palatine, maxillary and premaxillary bones, and 

 is fixed ; the lower jaw consists of two rami, which are simple or 

 formed by one bony piece, and are articulated by a convex or flat 

 condyle to the base of the zygomatic process, and not to the tym- 

 panic element of the temporal bone ; the base of the coronoid 

 process generally extends along the space between the condyloid 



