400 



UNGULATA 



re 



Fig. 166. — Under surface of the liver of the Horse, u, Umbilical 

 assure ; //, left lateral lobe; Ic, left central lobe; re, right central 

 lobe ; rl, right lateral lobe ; s, Spigelian lobe ; c, caudate lobe. 



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 the spleen, 

 and a shorter right 

 lobe. The principal 

 duct enters the 

 duodenum with the 

 bile-duct, and there 

 is often a second 

 small duct which 

 opens separately 

 near to this. 



Circulatory and Respiratory 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 Ehinoceros, 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 



