374 COMPARATIVE SPLANCHNOLOGY. 



In the smaller ruminants there is formed a ductus communis. The camel has 

 no gall bladder. 



The pancreas presents no comparative feature of interest, excepting that its 

 duct forms in the ox no ductus communis, but enters the duodenum separately. 

 The spleen is of one thickness throughout, with two rounded extremities ; it 

 adheres to the left side of the rumen and the diaphragm, but is not supported 

 by the great omentum. 



RESPIRATORY SYSTEM. 



The nostrils are narrow, and are capable of little dilatation compared with 

 those of the horse. The nasal fossae differ chiefly in there being an additional 

 third turbinal, the olfactory fossa, and in the arrangement of the frontal sinuses, 

 which extend over the cranium, and are continuous with the cavities in the horn 

 cores (see p. 100). The nasal chambers communicate at the posterior nares 

 below the inferior border of the vomer, and each of them contains a structure 

 called the canal of Jacob son, communicating with the mouth. It commences 

 in the floor of the nasal chamber, at the base of the septum, on each side of the 

 vomer, proceeds forwards, and terminates behind the pad in front of the palate. 

 It contains a number of mucous follicles ; its use is unknown. The larynx is 

 simpler in structure, the lateral ventricles and true vocal chords being only 

 slightly developed. The trachea presents no important variation. We may 

 note the presence of a third bronchus, which passes to the right lung to supply 

 a lobe which is wanting in the horse. 



The thoracic cavity is relatively smaller in the ruminant, and the pleurse 

 present a very important deviation from the arrangement found in the solipede 

 viz., the posterior mediastinum is imperforate and strong, completely separ- 

 ating one pleural sac from the other. This arrangement exists in all the 

 domesticated mammals but the solipede. 



The left lung is divided into two lobes, the right into four, the anterior one 

 recurving over and almost covering the front of the heart. The interlobular 

 cellular tissue is exceedingly thick, the separation between the lobules being 

 distinctly visible. This arrangement explains perfectly the special nature of 

 pneumonic lesions in the larger ruminants. 



URINARY SYSTEM. 



In the comparative anatomy of the kidney, the chief variation from the 

 simple type consists in the gland being more or less divided or lobulated. 

 In some animals the kidney is so lobulated as almost to resemble a bunch 

 of grapes, each lobule having its own blood-vessels and excretory duct. This 

 subdivision is constant in all animals in early foetal life ; but in the majority, 

 the parietes of the lobules coalesce, and the organ becomes a single mass. The 

 kidney of the ox is intermediate in form, the medullary or inner substance 

 of the organ being united, while the cortical or outer substance is divided 

 into lobes. The pelvis consists of a principal cavity, with a diverticulum or 

 calyx for each lobule, the uriniferous tubes of each calyx opening on a papilla. 

 The general form of the gland is ovoid and elongated ; in the smaller rumi- 



