290 



MAMMALIA. 



Snd 



finally on the intercostal arteries and the iliac veins of the Dolphin. 



A renal-portal system is always absent. 



The lymphatic system is provided with numerous lymphatic 



glands, and its main trunk (ductus thoracicus), which is placed on 



the left, opens into the 

 superior vena cava. 



Of the so-called vascular 

 glands the spleen, the thy- 

 nms, and the thyroid, which 

 is especially developed in the 

 young, are very generally 

 present (fig. 675). 



The paired lungs (fig. 675) 

 are freely suspended in the 

 thoracic cavity, and are dis- 

 tinguished by the numerous 

 ramifications of the bronchial 

 tubes, the finest branches of 

 which end with conical, fun- 

 nel -shaped dilatations (in- 

 fundibula), which are pro- 

 vided on their lateral surfaces 

 with swellings. Respiration 

 is mainly effected by the 

 movements of the diaphragm, 

 which forms a complete, 

 usually transversely placed, 



FIG. 676. Circulatory apparatus of Man (from Owen septum between the thoracic 



after Allen Thomson). Vd, Right yentricle ; Vs, 

 left Ventricle ; Ad, right Auricle ; J&, left Auricle ; 

 Ao, Aortic arch ; Aod, descending Aorta ; Cd, right 

 Carotid; Cs, left Carotid; Sd, right eubclavian 

 Artery ; Ss, left subclavian Artery ; M, Mesenteric 



and abdominal cavities: by 

 the contraction of its mus- 

 cular parts it acts as an in- 



Vena Cava ; Vd, superior Vena Cava; JT, common 

 Iliac vein; Vp, Vena port* ; J3, right Jugular; 



Js, left jugular ; Svd, right subciavian Vein ; 



Artery; J7, common Iliac Artery; Va, inferior spiratory muscle ; that is, it 



j:i fl tpe thp fVioramV ravitv 



( 



The elevation and depression 

 of the ribs also have an effect 



Lungs ; L, Xiver ; N t Kidney ; D, Intestine. in dilating the thorax. The 



trachea is, as a rule, straight, without coils, and divides at its lower 

 end into two bronchi leading to the lungs. There may be, in addition, 

 a small accessory bronchus on the right side. The trachea is supported 

 by cartilaginous half -rings which are open behind, and only excep- 

 tionally by complete rings of cartilage. The first part of the trachea, 



