en * Prof. Owen on the Class. Mammalia. 
The blood-dises are smaller than in Reptiles, and, save i ‘ 
eamel-tribe, are circular. The night auriculo-ventricular valve 18 
membranous, at least never entirely fleshy; and the aorta bends 
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 continued 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 gener- — 
ly 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 com- 
pact figure than in the other vertebrate classes; their parenchyma — 
1s 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 cysti¢ 
uct, when it exists, always joins the hepatic, and does not enter — 
the [aay separately. ‘The pancreatic duct is commonly — 
single. = 
__ The mouth is closed by soft flexible muscular lips: the upper — 
jaw 1s composed of palatine, maxillary and premaxillary bones, — 
and is fixed; the lower jaw consists of two rami, which are sim- 
ple or formed by one bony piece, and are articulated by a con 
vex or flat condyle to the base of the zygomatic process, 2 
not to the tympanic element of the temporal bone; the base 
the coronoid process generally extends along the space betweet 
the condyloid and the alveolar processes. The jaws of Mammals, 
with few exceptions, are provided with teeth, which are arrange 
in a single row; they are always lodged in sockets, and never 
Ps 
lottis: the rings of the trachea are generally cartilagi 
incomplete behind: there is no inferior larynx. The cesop! 
is continued without partial dilatations to the stomac 
varies in its structure according to the nature of the f 
quantity of nutriment to be extracted therefrom. 
