SKULL — BIRDS 



173 



An anlorbital plate arises from the side wall just in front of this fissure and forms 

 the hinder wall of the capsule, while later, the lateral wall and roof arise as 

 continuations of the median septum (in some the lateral wall starts as a separate 

 chondrification). Internally the capsule consists of an anterior atrium and a 

 wider posterior part with two conchae (turbinals), ingrowths from the lateral wall. 

 The mandibular arch consists of quadrate and Meckelian. The former lies 

 close to the otic capsule and consists of a body with a pterygoid process, directed 

 anteriorly and medially, which is soon reduced. An otic process appears a little 

 later, extending to the region of the anterior semicircular canal, differentiating 

 later into two parts for articulation with the capsule and with the squamosal 

 respectively. The lower end of the quadrate has two condyles to fit correspond- 

 ing surfaces on the head of the Meckelian. The two Meckel's cartilages are 

 widely separate anteriorly at first, gradually growing together, in Mdopsitlacus 

 bv the intervention of a copular cartilage. 



Fig. 186. — Later chondrocranium of chick with membrane bones (Tonkoff, in 

 Gaupp, '05). an, angular; ao, antorbital cartilage; d, dentale; /, frontal; ios, orbital 

 septum; >«, maxilla; n, nasal; oc. otic capsule; p, parietal; pi, palatine; pf, prefrontal; 

 plsp, sphenolateral; ptn, prema.xilla; q, quadrate; qj, quadratojugal; sa, surangulare; 

 sq, squamosal; 2, zygomatic. 



The accounts of the development of the hyoid apparatus are contradictory 

 and leave many points uncertain. The hyoid arch (fig. 187, B) arises as two 

 separate parts on either side, one closely associated with the cranium, the other 

 in the pharyngeal floor. The latter adjoins a median copula; statements differ 

 as to its fate. Usually it is said that the copula forms a small projection (ento- 

 glossum) near the anterior end of the apparatus, but others say that this arch 

 unites with the copula, and in parrots furnishes the loop on the upper side of the 

 copula. This statement also recognises a pair of separate paraglossal cartilages 

 near the end of the copula, which, with the copula, form the entoglossum which 

 often is bifid at the tip. The larger cornu arises from the first branchial arch 

 and divides early (usually) into two elements (sometimes three), variously 

 called hypo- and ceratobranchial or cerato- and epibranchial. The copula 

 sometimes has connected with it posteriorly a pair of subcopular cartilages 

 which unite and give attachment to muscles. 



