96 ME. W. a. EIDEWOOI) ON" THE HTOBEANCHIAL 



eacli approximately resembling in sliape the half of a longitu- 

 dinally divided egg-shell. The cartilage is thin and fairly uniform 

 throughout, and is perforated ventrally by the three branchial 

 slits sloping obliquely outwards, backwards, and slightly upwards. 

 The two cartilages are closely applied one to another in the 

 median plane for about one-half of their length. Their applied 

 faces are nearly flat, and are readily separable, no fusion having 

 yet taken place. The two cartilaginous basket-works look 

 upwards and slightly inwards, and the inner and anterior edges 

 are involute. Of the three branchial clefts the first is situated 

 about halfway from the anterior end, so that in front of it 

 there is quite a large extent of unbroken cartilage. This latter 

 represents the first branchial arch of the tadpole of the frog^ 

 The length of the most anterior cleft is about one-half of the 

 transverse diameter of the basket. The second and third clefts 

 are nearly parallel with the first : they are successively shorter^ 

 and lie rather closer to the median line. The two bars of 

 cartilage separating the three clefts are the second and third 

 branchial arches, while the cartilage bounding the last cleft 

 posteriorly represents the fourth branchial arch of the frog- 

 tadpole. Seeing that in fishes the cleft is situated in front of the 

 arch of the same denomination (i. e. that the first branchial cleft 

 is bounded behind by the first branchial arch, and so on), the 

 three clefts here present represent the second, third, and fourth 

 branchial clefts respectively. It may seem unnecessary to insist 

 on this point ; but when three clefts occur, as here, in a continuous 

 cartilage, there is a temptation to speak of them loosely as the 

 first, second, and third, and then arises a danger of losing sight 

 of their morphological enumeration. 



The inner or pharyngeal surface of the branchial cartilage ia 

 not smooth, but is covered with a multitude of minute, blunt, 

 arborescent growths. These are not shown in the figures. There 

 are also sharply defined ridges running along the upper surface 

 of the second and third branchial arches, and continued over the 

 undivided cartilage both outwards, backwards, and upwards, to 

 the external edge, and inwards, forwards, and upwards, to the 

 internal overhanging border. These latter processes are evidently 

 equivalent to those outgrowths in the branchial apparatus of the 

 Mana tadpole which Graupp calls spicula ii. and iii. (14. Taf. xvii. 

 fig. 1), and to which Parker (34) attaches undue importance by 

 calling them the true branchial arches. The fiap-like outgrowth 



