488 Vertebrata. 



large intestine, tlie end portion alone being termed rectum. 

 A c se c u m almost always arises from the large intestine at its 

 junction with tlie small intestine ; in some animals, {e.g., the Horse), 

 it attains an enormous length, whilst in others {e.g., Man), it is 

 small, or even rudimentary* The liver, which is situated behind 

 the diaphragm, is usually, but not invariably, provided with a 

 gall bladder (it is wanting in, e.g., the Horse), The pancreas 

 has generally one duct,t which opens into the anterior portion of the 

 small intestine, either together with, or independently of, the bile 

 duct. J 



Respiratory Organs. The entrance to the larynx is a 

 longitudinal slit behind the tongue, anterior to the entrance into the 

 oesophagus. In front of the opening, there is a peculiar flap, the 

 epiglottis, which contains a large elastic cartilage ; under ordinary 

 conditions it is directed forwards, often reaching even up over 

 the edge of the soft palate (Fig. 396), but when food passes from the 

 mouth through the pharynx into the oesophagus, the epiglottis is let 

 down over the glottis. The walls of the larynx are supported by 

 large cartilages, viz., the cricoid behind, the large thyroid 

 below; in front and above, the two arytenoids. The rest 

 of the trachea is usually strengthened for some distance 

 by cartilaginous rings ; it branches posteriorly into two large 

 bronchi, which branch again ; each lung, as already stated, is an 

 arboriform organ, of which both the larger and finer branches are 

 hollow. Only the peripheral branches, which have thin walls, and 

 are furnished with small dilations (alveoli) are respiratory ; in 



other regions the tubes have thicker walls, 

 provided in the larger branches with 

 cartilaginous rings like those of the 

 trachea, or with small cartilaginous plates. 

 All the branches are held together by 

 connective tissue. The lungs, with the 

 heart, are situated in the anterior portion 

 of the body-cavity, the thorax, along 

 ■CI- oAB o 11 ^ J, the dorsal wall of which the oesophagus 



Fig. 397. Small portion of a .. '^ 



Mammalian lung fiUed passes; whilst the rest of the alimentary 

 with mercury, a finest bronchial ^anal, with the kidneys and reproductive 



tuDS, respiratory portion of ■" , . . , 



the lung.— After Frey. Organs, lies in the posterior portion, the 



abdomen. A large septum, the dia- 

 phragm, divides the thorax from the abdomen; it is tendinous 



* In Man and some other Mammalia, the cseoum is continued into a thin narrow 

 appendage, the processes vermiformis. 



t Occasionally the pancreas has two duets, which either open both direct into the 

 gut, or one unites with the bile duct. 



J The great omentum is a specially developed portion of the mesentery, depending 

 in many forms over the ventral side of the stomp oh and the intestine. 



