206 THE FROG. 



of the quadrate turns sharply inwards, QR, and is connected with 

 i he 1 rabecula just in front of the ear capsule, EC. From the outer 

 edge of the quadrate the prominent, vertical, orbital process, qo, 

 projects upwards ; and the anterior end of the quadrate, like its 

 posterior end, turns sharply inwards, to form the palato-pterygoid 

 bar, qp, which is fused with the trabecula, between the nose and 

 the eye. The quadrate may thus be described as a horizontal 

 bar of cartilage, lying to the outer side of the trabecula, and 

 connected with this by two struts, one in front of the eye and 

 one behind it. 



The second segment of the mandibular bar, or Meckel's 

 cartilage, MC, is a short, stout bar of cartilage, which runs 

 inwards and forwards across the floor of the mouth. The third 

 segment, or lower labial cartilage, LL, is a much smaller bar at 

 the inner end of Meckel's cartilage, which meets, or is actually 

 fused with, its fellow of the other side in the median plane. 



The chief further changes that occur in the mandibular bar 

 during the later periods of tadpole life (cf. Fig. 93) : — are (i) a pro- 

 gressive diminution in size of the orbital process, qo ; and (ii) the 

 development of an additional connection between the hinder end 

 of the quadrate and the auditory capsule, by means of an otic 

 process (Fig. 93, qe). 



At the time of the metamorphosis, very considerable and 

 important changes take place, which will be described later on. 



The hyoid bar appears directly after the mandibular bar, and 

 immediately behind this. At first the right and left bars are 

 separate ventrally, but they soon become connected by a median 

 plate. The hyoid bar thickens rapidly, and at 12 mm. (Figs. 

 90, 92) forms a broad, somewhat S-shaped plate of cartilage, the 

 ceratohyal, hr, which lies across the floor of the mouth. The 

 outer end of the ceratohyal is enlarged, and turned upwards, and 

 articulates with the ventral surface of the quadrate about the 

 middle of its length (Fig. 90, hq). The inner ends of the two 

 ceratohyals are connected, across the floor of the mouth, by a 

 median basihyal cartilage, hb, the posterior end of which grows 

 back as a keel-like urohyal process (cf. Fig. 65, hb), which 

 separates the two halves of the thyroid body from each other. 



The branchial bars are a series of four pairs of cartilaginous 

 rods, developed in the four branchial arches of each side. They 

 appear in order, from before backwards, as slender curved bands 



