THE SKELETON OF THE VERTEBRATE HEAD. 193 



of the so-called basi-glosso and uro-hyals in the bird remains 

 to be determined. 



The precise observations of Eathke have shown that the 

 lateral halves of the feebly-developed hyoid of the ophidian 

 are formed by the lower portions of the primordial cartila- 

 ginous streaks of the second pair of visceral laminae, while the 

 auditory columellse are formed in their upper portions. 

 Eathke also found that the primordial cartilaginous streaks of 

 the third pair of visceral laminae, and which are attached to 

 the occipital region, disappear altogether. 



There are no embryological observations in sufficient detail 

 to indicate the morphological relations of the more or less 

 complex hyoid apparatus in the chelonian and lacertian. 

 The so-called hyoid, or suspensory arch of the branchial 

 apparatus in the Amphibia, is developed in the second pair of 

 visceral laminae. The corresponding arch in the tadpole, and 

 the anterior or suspensory horn of the so-called " hyoid " of 

 the frog, are also developed in this pair of visceral laminae. 

 The suspensory arch of the branchial apparatus is attached to 

 the quadrate, or so-called " tympanic " piece of the mandi- 

 bular arch, and not to the base of the cranium. Eathke had 

 observed a filament extending between the auditory region of 

 the cranium and the quadrate cartilage of the tadpole. He 

 found that the so-called " malleus and incus " are developed 

 in this filament. According to Eeichert, this filament appears 

 to be the upper part of the second primordial cartilaginous 

 streak, which, in consequence of the peculiar manner in which 

 it curves forward superiorly towards the quadrate cartilage (a 

 curvature of the same kind towards the quadrate bone has been 

 observed by Eathke in the adder), becomes attached to it. In 

 consequence of this attachment, the hyoidean arch becomes 

 suspended to the quadrate portion of the mandibular ; and the 

 upper portion, between the quadrate cartilage and the auditory 

 region of the skull, becomes converted into those elements in 



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