DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 229 



and ends blindly a short distance from the blind end of the efferent 

 vessel, and in a direct line with this. 



"We shall consider the accounts given by other investigators con- 

 cerning the lingual artery at the conclusion of our description of the 

 next stage, 12 mm. Here we may mention that we have paid very 

 special attention to its early development, and are quite satisfied that 

 at 9 mm. its condition is as described and figured here : at this 

 period it has no communication with any other vessels. Further- 

 more, we have failed to detect it at any earlier stage, except an 

 immediately preceding one ; and are satisfied that in Bana temporaria 

 it does not arise from any part of the vessels which we have described 

 in the earlier stages as belonging to the hyoid and mandibular arches. 

 The distance to which the lingual artery can be traced forwards in 

 the floor of the mouth varies in different specimens, but this variation 

 we believe to be connected with the rapid growth forward of the 

 artery after its first appearance. 



In Fig. 11, the lingual artery, A L, appears to have very close 

 relations with the hyoid and mandibular veins, V Y and V M. 

 There is really a considerable interval between them, the artery 

 being much nearer the median plane than the veins. Part of the 

 hyoidean vein is represented as cut away in order to show the 

 dilated part of the lingual artery, which would otherwise be hidden 

 by it. 



d. The Second Branchial Arch. — The vessels of this arch are 

 practically identical with those of the first arch, and need not be 

 described in detail. The course and relations of the several vessels 

 are the same, and the vessels are of equal size, or if anything slightly 

 larger than those of the first arch. The afferent vessel bears, ventral 

 to the gill, a series of small sacculations (Fig. 11, A F.2) forming 

 the rudiments of the internal gills, which are similar to but rather 

 more prominent than those of the first afferent vessel. 



e. The Third Branchial Arch. — The afferent vessel (Figs. 11 and 

 12, A F.3) is of good size, though smaller than those of the first and 

 second branchial arches. It runs outwards to the small external 

 gill, dilates rather suddenly as it enters it, and then runs along the 

 posterior border of the gill to its tip, where it communicates directly 

 with the efferent vessel. It gives off loops to the lobes of the gill, 

 similar to those of the anterior arches. 



