REPTILIA. 



575 



Fir.261. 



comes converted into the permanent and comparatively simple os 

 hyoides of the Salamander, depicted in Jig. 260, D. 



The branchial arches 2, 3, 4, Dr. St. Ange remarks, are ab- 

 sorbed in proportion as the circulation becomes modified, their 

 atrophy depending upon the change which takes place in the 

 course of the blood, owing to the dilatation of the anastomotic ves- 

 sels (Jig. 259, e, e, e), and the enlargement of the pulmonary arte- 

 ries (b). It is, therefore, owing to a kind of revulsion produced 

 by the afflux of the blood towards the pulmonary organ, instead of 

 towards the branchiae, that the atrophy of the branchial capillaries, 

 and subsequently of the whole branchial apparatus, is produced. 



(632.) We must, 

 in the last place, before 

 leaving the considera- 

 tion of the circulating 

 system of the REP- 

 TILIA, describe that of 

 the Lepidosiren, a crea- 

 ture so exactly interme- 

 diate between the two 

 classes, that it is really 

 difficult to determine 

 whether it ought most 

 properly to be called 

 a fish provided with 

 lungs, or a reptile with 

 the circulatory organs 

 of a fish. 



The heart resembles 

 that of a fish, and con- 

 sists of a single auricle 

 (fg. 261, a), a ventri- 

 cle (6), and bulbus 

 arteriosus (c). The 

 vena cava (e), bringing 

 the vitiated blood from 

 the system, terminates 



at once in the auricle, which is represented in the figure as laid 

 open ; but the pulmonary vein (/), whereby the aerated blood 

 is brought from the lungs (w, m), passes along as far as the 

 auriculo-ventricular opening, where it empties its contents into the 



