THE SKELETON OF THE VERTEBRATE HEAD. 179 



In all the forms, I believe that traces of the intermediate or 

 temporal centrum may be detected, either in the cartilaginous 

 or osseous condition. In fishes, more or less of the primordial 

 cartilage remains above the junction of the occipital centrum, 

 post-sphenoidal centrum, and temporal neurapophyses (" petro- 

 sals"), and covered more or less internally, or towards the 

 cranial cavity, by the internal prolongations of the occipital 

 centrum, and of the temporal and post-sphenoidal neurapo- 

 physes. The peculiar canal for the muscles of the orbit 

 existing in certain fishes, and which is roofed over principally 

 by the " petrosals," or temporal neurapophyses, appears to be 

 hollowed out principally in the primordial temporal centrum, 

 and to be lined by its constituent cartilage. The peculiar Y- 

 shaped bone met with in the pike, perch, and salmon, marked 

 9 1 by Professor Owen, and * by Hallman, and considered by 

 the former as that portion of the pre-sphenoidal centrum which 

 results from the ossification of the corresponding central por- 

 tion of the notochord, appears to me to be a central element, 

 but referable rather to the post-sphenoidal or temporal than 

 to the pre-sphenoidal segment. For, in the first place, it may 

 be questioned whether the corda dorsalis of the fish reaches 

 the region of the pre-sphenoid ; and, in the second place, if I 

 am correct in my determination of the post-sphenoidal and 

 temporal neurapophyses of the fish, the two ascending limbs 

 of this bone abut against these latter elements, and are not at 

 all connected with the pre-sphenoidal neurapophyses. As, 

 moreover, these ascending limbs of the bone in question are 

 more intimately connected with the bones which Professor 

 Owen considers to be the ali-sphenoids, but which I must hold 

 to be the inferior temporal neurapophyses, I am inclined to 

 conceive it an ossified portion of the temporal centrum. 



With regard to the bone termed by Hallman os innomi- 

 natum, which is small but well marked in the carp, and larger 

 in the perch, and which Professor Owen considers to be the 



