162 ANIMAL BIOLOGY. [Part I. 



sorium. In the fowl the proximal portion forms the quadrate 

 bone, the succeeding portion in the lower jaw ossifying 

 as the articular. In the rabbit it seems probable that the 



s.m.p 



l^.v.cl. 



Fia. 52. THE MANDIBULAR ARCH. 



a. Point where fronto-nasal process overarches the nasal groove, fn. p. 

 Fronto-nasal process, i. m. p. Inferior maxillary process, m. Mouth, n. p. 

 Nasal pit. s. m. p. Superior maxillary process. 1st v. cl. First visceral cleft. 



proximal portion, answering to the quadrate of the fowl, 

 separates early and ossifies as the incus, while the succeeding 

 portion, answering to the articular of the fowl, is segmented 

 off from the rest of Meckel's cartilage, and ossifies as the mal- 

 leus ; while the main mass of the lower jaw is ossified (perhaps 

 in connection with lower labial cartilages) around, but not within, 

 the remainder of Meckel's cartilage. It may be, however, that 

 ossification of the most distal portion of Meckel's cartilage takes 

 place. Concerning the homologies of the quadrate, articular, 

 malleus, and incus, more than one interpretation has been offered. 

 The uppermost end of the hyoid arch would seem to be 

 segmented off and to ossify as the stapes, while the columella of 

 the frog and fowl are also developed from this arch. The 

 remainder of the arch forms the anterior cornua of the hyoid, 

 the basi-hyal giving rise to the body. The posterior cornua of 

 the rabbit and the fowl are remnants of the first branchial arch, 

 but in the frog of the fourth branchial arch, the third and first 

 two being represented by processes of the hyoid plate, the 



