632 J. PLAYFAIR MCMURRICH. 



turns abruptly upwards towards the base of the skull, parallel 

 to the first branchial arch. This is probably the genio- or 

 basihyal. 



The branchial arches (Brs.) remain the same practically as 

 in the last stage, and throughout show very little differentiation. 

 Another cartilage, however, makes its appearance at this stage, 

 which, though not at present connected with the visceral 

 cartilages, eventually unites with them. It consists (fig. 2, 

 E. Pa.), on either side, of a cartilaginous rod, articulating with 

 the sides of the rostral cartilage, near its anterior extremity, 

 and extends backwards and slightly downwards. It is the 

 commencement of the ethmopalatine cartilage. 



The principal change to be noted in Stage c (fig. 5) is the 

 growth of the pterygo-quadrate cartilage. It has now grown 

 upwards and expanded at the extremity with an anterior and 

 posterior process. The anterior is clearly connected with the 

 ethrao-palatine by a band of connective tissue, and represents 

 the pterygoid portion, while the posterior one has no connec- 

 tions, but probably is the future metapterygoid. Another 

 point is clearly noticeable at this stage, which helps in no 

 small degree to indicate the homologies of the cartilages. The 

 symplectic does not meet the basal portion of Meckel's carti- 

 lage ; the only cartilage articulating with this being the 

 quadrate portion of the pterygo-quadrate. In previous stages 

 this meeting and articulation seems to exist, or, at all events, 

 the two cartilages are almost in contact, but now their want of 

 union can be clearly seen. 



The growth of the pterygo-tjuadrate constitutes again the 

 most noticeable feature when we examine Stage d. In this it 

 is seen that the pterygoid process has grown so far forward, 

 and the ethmopalatine so far backward, that they are now 

 separated only by a very small portion of connective tissue. 

 The growth has been mainly, however, on the part of the 

 pterygoid process. The metapterygoid process has grown back- 

 wards only a short distance, and at this stage does not form a 

 buttress to the hyomandibular, as in the salmon. In the pre- 

 ceding stage, but more clearly to be seen in this, one can 



