VASCULAR SYSTE]*I. 



511 



tricle and auricle (sometimes as in Halicore the division is marked 

 externally). It is enclosed in a pericardium, and sends off an 

 arterial trunk, which forms a left aortic arch, from which two 

 vessels frequently arise, viz. (1) a right anonyma, with the two 

 carotids and right subclavian ; and (2) the left subclavian ; or, 

 as in man, three vascular 

 trunks, viz. (1) a right 

 anonyma, with the right 

 carotid and right subcla- 

 vian ; (2) the left carotid ; 

 and (3) the left subcla- 

 vian, all close to one 

 another. As a rule, one 

 superior vena cava (right) 

 and an inferior vena cava 

 open into the right aur- 

 icle ; more rarely, as in 

 the rodents, monotremes, 

 and elephants, etc., there 

 are two superior venae 

 cavae. Retia mirabilia 

 have been recognised 

 principally for the ar- 

 terial vessels, and are 

 found on the extremities 

 of burrowing and climb- 

 ing animals {Stenofs, 

 Myrmecophaga, Brady- 

 fus, etc.) ; on the caro- 

 tids round the hj^ophy- 

 sis, and on the ophthal- 

 mic arteries in the orbit 

 in ruminants ; finally on 

 the intercostal arteries 

 and the iliac veins of the 

 dolphin. The red blood 



corpuscles are devoid of a nucleus and are discoidal, except in the 

 Camelidae in which they are elliptical. They vary in size : in 

 man they are 3-0V0 ^^ of an inch ; in the elephant ytw^^^^ of an 

 inch ; they are smallest in the chevrotains in which they are 



Fro. 26?. — circulatory apparatus of man (from 

 Owen, after Allen Thom'^on). Ad right auricle ; 

 Ao aortic arch ; Aod descending aorta ; Aj> pul- 

 monary artery ; As left auricle ; Br bronchi ; 

 Cd right carotid • Cs left carotid ; D intestine; 

 Jd right jugular ; Jl common iliac artery ; J I 

 common iliac vein ; Js left jugular ; L liver ; 

 M mesenteric artery ; N kidney ; P lungs ; Sd 

 right subclavian artery ; Ss left subclavian artery ; 

 Srd right subclavian, Svs left subclavian vein; 

 Tr trachea ; Va inferior vena cava ; Vd superior 

 vena ca\a ; Vd right ^entricle ; Vp vena portao ; 

 Vpu pulmonary vein ; Vs left ventricle. 



