OF THE EESPIKATION. 
63 
part of the liver, which projects as a point. This vena cava 
runs a short distance, and enters as a principal part in the 
formation of that venous sac described above, which com- 
municates with the right auricle, and in which several other 
veins terminate : a species of valvules are observed at the 
mouth of each of these veins. ^ 
The heart of Ophidians has constantly on its upper sur- 
face a conglomerate gland, more or less in size, and sur- 
rounded by several other glands differing much, according 
to the species, in form and number. This first gland has 
been regarded by several naturalists as analogous to the 
th3rm.us ; by others, and I am of this number, it has been 
compared to the thyroid, t 
OF THE RBSPIEATIOlSr. 
To obtain an idea of the respiration of Ophidians, we 
must examine with attention a serpent in the state of repose. 
We then observe that the trunk contracts and dilates alter- 
nately by the play of the ribs, and that the movements are 
slowly repeated at regular intervals ; but we observe also, 
that the nostrils remain closed during this operation, and 
only open at considerable intervals, during which the body 
often has contracted thirty times. It results from these 
remarks, that the lungs of Ophidians, besides their ordinary 
function, have to act as a reservoir for atmospheric air : 
this reservoir, filled by a single inspiration, contains a suf- 
ficient quantity of air, in order that the oxygenation of the 
blood can take place by the contractions of the lungs, with- 
out the necessity of a new inspiration, which only follows 
the expulsion of the air contained in the lungs, from which 
the oxygen has been totally absorbed. 
The structure of the lungs of Ophidians clearly proves 
what we advance ; it is chiefly remarkable for two circum- 
stances, because the lung usually terminates in a blad- 
- The description of the organs of circulation has been chiefly taken 
from the Boa constrictor. For further details consult the labours of 
Cuvier, Legons d’Anat, Comp., vol. iv. ; Schlemm, in Tiedemann Zeit- 
schrift,Yo\. ii., p. l,pl. 7 ; Retzius’ Schwed Verhandl,, 1830, and the Isis, 
1832, p. 524 ; Meckel, System, \o\. v, p. 218. 
t Consult the excellent memoir of Haugstedt, entitled Thymi Dcr^ 
scriptio, p. 152. 
