400 UNGULATA 
right lateral lobe. In most works on the anatomy of the Horse this 
has been confounded with the Spigelian lobe of man. There is no 
gall-bladder (as in 
all other Perisso- 
dactyles), and the 
biliary duct enters 
the duodenum 
about 6 inches from 
the pylorus. The 
pancreas has two 
lobes or branches— 
a long one passing 
to the left and 
reaching thespleen, 
and a shorter right 
lobe. The principal 
duct enters the 
duodenum with the 
bile-duct, and there 
is often a second 
Fic. 165.—Uniler surface of the liver of the Horse. wu, Umbilical small duct which 
fissure ; lJ, left lateral lobe; lc, left central lobe; rc, right central opens separatel 
lobe; rl, right lateral lobe; s, Spigelian lobe; c, caudate lobe. pe ep y 
near to this. 
Circulatory and Resyirutory Organs.—The heart has the form of a 
rather elongated and pointed cone. There is one anterior vena cava, 
formed by the union of the two jugular and two axillary veins. 
The aorta gives off a large branch (the anterior aorta) very near its 
origin, from which arise—first, the left axillary, and afterwards the 
right axillary and the two carotid arteries. 
Under ordinary circumstances the Horse breathes entirely by 
the nasal passages, the communication between the larynx and the 
mouth being closed by the velum palati. The nostrils are placed — 
laterally, near the termination of the muzzle, and are large and 
very dilatable, being bordered by cartilages upon which several 
muscles act. Immediately within the opening of the nostril, the 
respiratory canal sends off on its upper and outer side a diverti- 
culum or blind pouch (called “false nostril”) of a conical form, and 
curved, 2 to 3 inches in depth, lying in the notch formed between 
the nasal and premaxillary bones. It is lined by mucous mem- 
brane continuous with that of the nasal passage, but its use is not 
apparent. It is longer in the Ass than in the Horse. A similar 
structure is found in the Rhinoceros, and in a much more developed 
condition in the Tapir. Here may be mentioned the guttural pouches, 
large air sacs, diverticula from the Eustachian tubes, and lying 
behind the upper part of the pharynx. These are likewise found 
in other Perissodactyles, but their use is also still not clearly 
