REPTILIA. 573 



evidently goes to the branchiae, and a very small part to the 

 lungs. 



The reader must, however, here remark, that there are small 

 anastomosing vessels (e, e, e), uniting the branchial arteries with 

 the trunks of the branchial veins, and that these are situated 

 just at the roots of the gills, since these vessels become of the 

 utmost importance during the subsequent stages of the metamor- 

 phosis. 



The branchise gradually become diminished in size, and a smaller 

 quantity of blood passes through them, and as this goes on the vessels 

 (a, a, a ; f,f->f) shrink in the same proportion. Meanwhile the 

 lungs are progressively more and more developed, and the pulmo- 

 nary artery (b) expands in an equal ratio. As the blood forces 

 its way with more difficulty through the branchise, the anastomos- 

 ing vessels (e, e, e) dilate, and a freer supply of blood is poured 

 into the pulmonary system ; until at last, when the lungs are fully 

 formed, and the branchial arteries (a, , a) and veins (/,/,/) 

 quite obliterated, all the blood necessarily passes immediately 

 through the anastomotic trunks (e, e, e), which of course then 

 represent the vessels (0,0, o) of the Menopoma (Jig- 257), and 

 the mode of respiration is thus completely converted from that 

 of a Fish into that of a true Reptile. 



(631.) But, during the progress of these changes in the dispo- 

 sition of the vascular system, others not less wonderful take place 

 in the form and uses of the entire hyoid apparatus, and, in those 

 muscles of the throat which are connected with the function of 

 respiration. 



The hyoid apparatus of the tadpole is, in fact, a very compli- 

 cated structure,* and, like that of the fish, supports the branchise, 

 and facilitates the entrance and expulsion of the water ; moreover, 

 by opening or closing at pleasure the communication which exists 

 through the branchial apertures between the mouth and the ex- 

 terior of the body, it thus allows air to be taken into the lungs at 

 pleasure. 



The os hyoides of the tadpole, at an early period of its deve- 

 lopem en t, supports four branchial arches (Jig. 260, A, 1, 2, 3, 4), 

 which bound three branchial fissures, through which, as in a fish, 

 the water escapes from the mouth. The branchial arches 2 and 3 



* Recherches anatomiques et physiologiques sur les organes transitoires et la meta- 

 morphose des Batraciens ; par J.G. Martin St. Ange. Annales des Sciences Naturelles, 

 vol. xxiv. 



