THE SKELETON OF THE VERTEBRATE HEAP. 189 



allusion to the remarkable iudication which it affords of the 

 signification of the quadrate bone, and articular piece of the 

 lower jaw... It affords, as it appears to me, sufficient evidence 

 that the quadrate bone of the l)ird is the homologue of the 

 mammalian incus, and that the articular piece of its lower 

 jaw is the homologue of that ossified portion of the upper end 

 of Meckel's cartilage, which in the mammal forms the slender 

 process of the malleus. 



The quadrate bone has been hitherto considered as the 

 homologue of the tjTupanic bone in the mammal, not only 

 from the proximity of the latter to the condyle of the jaw, 

 but chiefly from its presumed absence in the skull of the bird. 

 But there appears to me to be sufficient evidence of its exist- 

 ence, not only in the fibro-cartilaginous frame which connects 

 the margin of the tympanic membrane to the mastoid, lateral 

 occipital, and basi-sphenoid, but more particularly in the thin 

 well-defined lamina of bone, which, apparently united to its 

 fellow of the opposite side, forms the floor of the t}Tnpanic 

 cellular space in the broad posterior portion of the basi- 

 sphenoid. As these apparently united laminas are continuous 

 with the single cartilaginous Eustachian tube, below the 

 single or double osseous Eustachian orifice, I am induced to 

 believe that they will turn out to be the feebly-developed 

 representatives of the tympanic bones of the mammal. 



By a very beautiful analysis Professor Owen has proved 

 that the quadrate-jugal bone of the bird is the homologue of 

 the squamous portion of the mammalian temporal. I cannot, 

 however, give my assent to his determination of its special 

 homolog}'', as a portion of the subdivided radiating appendage 

 of the maxillary arch. Its relations in binls and crocodiles, 

 in which it presents all its fimdamental connections, appear 

 to me to show that it is an anterior actinapophysis of the 

 mandibular arch ; passing forwards to abut against the malar, 

 which I have already stated to be a jiosterior actinapophysis 



