XIII 



PHYLUM CHORDATA 



437 



veins similar to those forming the right, except that it has no 

 azygos branch. 



The post-caval vein (pt. c.) is formed in the hinder part of the 

 abdominal cavity by the union of the internal iliacs (i. il. v.) 

 bringing the blood from the back of the thighs. Shortly after 

 its origin it receives the two external iliacs (e. il. v.) bringing the 

 blood from the hind -limb. In front of this a pair of ilio-lumbar 

 (i.l.) veins join it ; a little farther forward a pair of spermatic (spm.) 

 (in the male) or ovarian (in the female) veins ; and opposite the 

 kidneys a pair of renal veins (?-.). From the liver the blood is carried 

 to the post-caval by the lupatw veins. A pair of small posterior 

 phrenic veins (p. ph.) bring the blood from the diaphragm and open 

 into the post-caval as it passes through the substance of the latter. 



The hepatic portal system consists, as in other Vertebrates, of a 

 system of veins conveying blood from the various parts of the 

 alimentary canal to the liver, the trunks of the system uniting to 

 form the single large portal vein (Fig. 1026, ^>. v.). The principal 

 veins of the portal system are the licno- gastric, duodenal, anterior 

 mesenteric, and posterior mesenteric. There is no trace of a renal 

 portal system. The red blood corpuscles are circular, bi-concave, 

 non-nucleated discs. 



Respiratory Organs. The larynx (Fig. 1029) is a chamber 

 with walls supported by cartilage, lying below and somewhat 



behind the pharynx, with 

 which it communicates 

 through a slit-like aperture. 

 The cartilages of the larynx 

 are, in addition to the 

 epiglottis, which has been 

 already referred to (p. 431), 

 the large thyroid (th.), which 

 forms the anterior wall, the 

 ring-like cricoid (c?*.), the 

 two small arytenoids (ary^ 

 and a pair of small nodules, 

 the cartilages of Santorini 

 (sant), situated at the apices of the arytenoids. The vocal cords 

 extend across the cavity from the thyroid in front to the arytenoids 

 behind. Leading backwards from the larynx is the trachea or 

 wind-pipe (Fig. 1025, tr.), a long tube the wall of which is supported 

 by cartilaginous rings which are incomplete dorsally. The 

 trachea enters the cavity of the thorax, and there divides into the 

 two bronchi, one passing to the root of each lung. 



The lungs (Fig. 1030) are enclosed in the lateral parts of the 

 cavity of the thorax. Each lung lies in a cavity lined by a 

 membrane the cavity of the 2 } ^ ura ^ sac or plcural membrane. 

 The right and left pleural sacs are separated by a considerable 



cr 

 tr 



FIG. 1029. Lepus cuniculus. Laiynx. A, 

 ventral view ; B, dorsal view. /?/. arytenoid ; 

 cr. cricoid ; (p. epiglottis ; sant. cartilage of San- 

 toriiii ; th. thyroid ; ^.-trachea. (From Krause, 

 after Schneider.) 



