144 On the. First and Second Visceral Arche*. [Apr. 2G, 



origin, namely, as a modification of the hyouiandibula, the primitive 

 proximal paramere of the second visceral arch. 



Successive Modifications of the Mandibular and Hyoidean Visceral 



Arches. 



I. Primitive condition (jSTotidanidae). The palato-quadrate bar 

 alone carries the mandible. The second arch is indifferent. Hyoman- 

 dibnla and qnadrate (the palatine part is an outgrowth) are both 

 attached to the cranium. 



II. The hyomandibula gains a fibro-cartilaginous connexion with 

 the mandible, the masticatory apparatus becomes amphistylic and 

 occasionally hyostylic (Rajidae. most Selachians). 



The hyoid gains a cranial attachment (many Rajidae). 



III. The quadrate- or autostylic suspensorium becomes preponde- 

 rant ; the hyomandibula is, as in Teleosteans, divided into a proximal 

 and into a distal (symplectic) element. The proximal partis received 

 into a fenestra of the otic capsule, and is converted into a stapes, whilst 

 the distal half either remains (Proteus, Siren, Menopoma) or is lost 

 (other Urodela). The whole hyomandibula would have been lost 

 owing to its excalation from suspensorial functions, unless it had 

 entered the auditory service. 



IV. The autostylic arrangement prevails. The whole hyomandibula 

 remains, gains an attachment on the " tympanum," and differentiates 

 itself into several conjointed pieces, notably stapes or columella 

 proper, and extra-columella or malleus. 



The extra-columella gains connexion with the parotic cartilage ; this 

 connexion frequently remains, but in Anvra alone it contains a special 

 element of probably parotic origin. 



The quadrate forms an important part of the tympanic frame. 



IV<x. Collateral departure of the Anura. The connexion between 

 the tympanal part of the hyomandibula with the mandible is lost. 



V. The quadrate still forms the principal suspensorial part of the 

 mandible. The extra-columella, or malleus, retains for a long time its 

 previously acquired connexion with Meckel's cartilage (Amniota). 



Ya. The top end of the hyoid is attached to the cranium (Gecko*. 

 Mammalia), and is occasionally fused with the extra-columella 

 (Hatteria). 



Yb. Or. the proximal portion of the hyoid is removed from the skull 

 and remains otherwise well developed (most Lizards); or its proximal 

 portion becomes reduced and lost (Chelonia, Crocodilia, Ophidia, Aves). 



Yc. The extra-columella gains an attachment to the quadrate, 

 squamosal, or pterygoid, whilst its connexion with the mandible 

 (Ophidia, Chameleon), and the tympanum, is lost. 



VI. The quadrate gradually loses its articulation with the man- 

 dible; the latter gairs a new outer articulation with the squamosal; 



