in the Fcetus of Vertehrated Animals. 101 



and appear to be processes of this bone, which are developed only 

 during fcetal life. At the same time, three clefts are formed be- 

 tween these arches on each side of the neck, and below the at- 

 tachment of the external gills, through which the water taken 

 into the pharynx is driven out by a muscular effort, so as to pro- 

 duce a current near the leaflets of the gills. It is only in the 

 latter stages of fa?tal development, however, that the aid of 

 these currents through the branchial Apertures is required, 

 owing to the existence in the earlier periods of a very singular 

 provision, lately discovered by my friend Dr Sharpey *, by 

 which, in the batrachian reptiles, as well as in all the mollusca 

 which he has examined, a constant renewal of water is pro- 

 duced, in contact with their respiratory surfaces. Dr Sharpey 

 has shown that, in the batrachia during the early stage of foetal 

 life, the integuments, and especially those parts on which 

 bloodvessels are minutely distributed, possess an inherent power 

 of producing currents in the water near them, without any 

 perceptible muscular action, of impelling, as it were, the water 

 along the surface, and thus forcing it to be constantly in motion. 

 This power of producing currents is strongest in the covering of 

 the gills themselves, but it also exists to a considerable extent in 

 other parts of the body, especially on the tail and lower part 

 of the abdomen •[•. 



A considerable time before the gills of the salamander arrive 

 at their full size, the rudiments of the lungs, the principal res- 

 piratory organs of the adult animal, begin to be formed. The 

 lungs may be perceived, according to Rusconi, about the 23d 

 day of the development of the embryo, and they have attained 

 a considerable size by the time that the gills are perfected. 

 About the 4.0th day they consist of two long shaped sacs situ- 

 ated behind the stomach, close to the vertebral column. They 

 do not contain any air for some time after their formation. 

 According to Rusconi, the larva of the salamander begins to 

 expel air from its mouth about the 30th day ; but it is difficult 

 to conceive how air can at this time be introduced into the lungs 



• On the Currents produced by the Respiration, &c. Edinburgh Medical 

 and Surgical Journal, 1830. 



t It would be interesting to know if any analogous power exists in the 

 body or gills of the foetus of those cartilaginous fishes in which external gills 

 are found. 



