272" PROF. W. K. PAEKEE OX THE STETJCTURE AND 



of the " pedicle," " ascending process," and " pterygoid cartilage ;" the falcate postero- 

 superior part of the quadrate is the " otic process " {ot. p). 



I find no rudiments of the " ethmo-palatine," such as are seen in other Sauropsida ; 

 they are probably, when present, merely detachments of the " pterygo-quadi-ate," and 

 not rudiments of a preoral arch. 



The hyoid arch (PI. LXVIII. fig. 9) is scarcely one fourth the size of the mandibular ; 

 it is also much more segmented, and corresponds very closely in its divisions with a 

 branchial arch. 



A side view (PI. LXVIII. fig. 9) shows that there are four pairs of segments besides 

 the basal rudiment, and of these, one, the " suprastapedial," is a special hyoid element 

 not found in normal branchial arches ; moreover, the distal piece of such an arch, the 

 " hypohyal," is not distinct in the Crocodilia from the common basihyo-branchial plate. 

 The uppermost segment or columella (co.= part of " pharyugo-hyal ") is like a drum- 

 stick ; its height is about three times as great as its thickness ; it is narrow in the middle, 

 and dilated at each end. The next is a short oval nucleus, the " suprastapedial " {s.st); 

 this is a special Crocodilian segment. The third, or " epihyal " {e.hy), unites the 

 pharyngo-hyal with the main piece ; above, this small curved rod is attached by 

 ligament to the uppermost piece '. 



The main bar, or " ceratohyal " {c.Iiy), is like a rib, with its " capitulum " and " tuber- 

 culum," and, like its proper homologue in the herbivorous Mammalia, carries the 

 epihyal ; it is also tied to the columella ; it lessens downwards, becoming terete, and 

 is thoroughly fused below with the mandible, close behind the articulation with the 

 quadrate (fig. 9, c.hy, q, ar) ; it is a gently sinuous bar. The rest of this arch, at 

 present, is merely a median hyo-branchial tract (PI. LXVIII. fig. 7, h.h.br), the hyoid 

 part of which lies in front of the " first ceratobranchials " {c.hr^), or paired " thyro- 

 hyals." 



These segments are to be seen in the subhorizontal sections ; in one which takes the 

 notochord and investing mass through their common plane (PL LXIV. fig. 4), the 

 relation of the mandibular and hyoid arches to the tympanic cavity (first cleft) and 

 auditory capsule is well shown. The cavity widens as it passes forwards between the 

 quadrate {([) and the auditory capsule (««) ; a lesser space is seen passing behind at an 

 acute angle from the front parts, and running behind the quadrate and the joints of 

 the hyoid arch. A thin shaving of the columella {co) or pharyngo-hyal is seen running 

 inwards so as to touch the auditory capsule ; thus the top of the main part or cerato- 

 hyal [c.hy) is seen, and behind it the small epihyal [e.hy) is cut through. 



Another very similar section (PI. LXVIII. fig. 3) is still more instructive ; it is a 

 little higher up, and the columella (co) is seen fitting into the side of the auditory 

 capsule exactly as its counterpart (the hyo-mandibular) does in the Selachians. Here 

 the " suprastapedial " {s.st) is cut across above the top of the ceratohyal {c.hy). 

 ' This separate " suprastapedial" has not turned up in any other type. 



