THE LIZARD. 163 



145. The thyroid gland (M), a whitish, transversely 

 elongated body on the ventral wall of the trachea, a short 

 distance in front of the heart. 



146. The right precaval vein (Fig. 43, p. 172, /?-.<;), 

 situated in the lateral region of the neck, and passing back- 

 wards towards the right side of the heart (see 200) : it is 

 formed by the union of three veins; the internal jugular 

 (Figs. 40 and 43 i.ju), coming from the lateral region of the 

 head and bringing blood from the brain, &c. ; the external 

 Jugular (e.ju\ situated in the middle ventral line of the 

 throat, and at its hinder end turning to the right to join the 

 internal jugular; and the subclavian (sd.v), bringing 

 blood from the right fore-limb. 



147. The left precaval, formed by the union of the 

 left internal jugular and left subclavian veins : the left 

 external jugular is absent. 



148. The position and relation of the hyoidean apparatus 



.( 79-83). 



XVIII. Make a longitudinal vertical incision through 

 the liver, beginning at its anterior border, a little to 

 the left (the animal's left, your right) of the post- 

 caval, and passing backwards to the right of the 

 epigastric vein and gall-bladder : in this way the 

 whole postcaval is left uninjured on the right side, 

 and the gall-bladder, with its duct ( 165), and portal 

 ( 161) and epigastric veins, on the left. 1 Note 



149. The stomach (Fig. 40, j/), hitherto concealed 

 beneath the liver : it is a tubular organ, of slightly greater 

 diameter than the intestine, and with thick, muscular walls. 



1 This method of dissection is adopted because of the connection of 

 the liver to the dorsal body- wall by blood-vessels ( 163, 164), which are 

 ruptured if the liver is turned forwards in the ordinary way : in fresh, un- 

 injected specimens there will of course be a good deal of bleeding, but this 

 objection does not apply either to injected or to spirit specimens, 



M 2 



