250 
The 214, 33, 4th and 5 vertebrae are fused in the adult: they are 
the 2"dand 3" vertebrae of Weber. The 5* is the most independent, 
especially as to its arch and neural spine, and in young forms readily 
separates from the 42. 
The reduction affecting the incus noted above has extended to the 
rest of the 2"lvertebra so that no trace is left in the adult, except a 
little cartilage in the region of the neural spine. — The body serves 
apparently merely to deepen the anterior cavity of the third vertebra, 
although in horizontal sections through fish of 3—4cm length, the 
204 and 3" vertebrae appear of almost equal size. 
The usual intervertebral growth of the notochord does not take 
place between the 3" and 4 vertebrae so that the posterior cone of 
the one and the anterior cone of the other are only very incompletely 
developed, and very little trace of the notochord is left between the 
two vertebrae in the adult. The limit between the bodies is marked 
however by a rough ridge which serves for the attachment of the air- 
bladder. The transverse processes of the 3'4 vertebra are converted 
into the mallei, the arches are ossified as is the strong neural spine 
which projects forwards and receives in its bifid extremity the supra- 
occipital above the foramen magnum. The 4t*and 5* vertebrae to- 
gether form as much as */,t% of the length of the bone which results 
from the fusion of the 224, 374, 4thand 5% vertebrae. |The suture be- 
tween the centra is often obscured in the adult on the outside by the 
formation of superficial ossifications corresponding to the attachment 
of the air-bladder but is always evident in the neural canal. 
The transverse processes of the 4!tare of great size forming on each 
side a flattened plate which projects horizontally outwards from the 
body, and possesses a thick anterior edge suturally united with the trans- 
verse portion of the supraclaviculare. — Thus like the mallei the trans- 
verse processes of the 4'%project considerably in front of the vertebra 
to which they belong. — The ventral surface of the thickened anterior 
edge serves for the attachment of the air-bladder; and the dorsal sur- 
face of the whole plate for the insertion of muscles. 
The Emergence of the Spinal Nerves. 
The roots of the anterior spinal nerves emerge through indepen- 
dent apertures in the arches of the vertebrae. The 15*spinal nerve 
emerges through the occ. lat., the 2"4 and 3'X very close to each other in 
the membranous wall of the neural canal between the ascending process 
of the stapes and the anterior margin of the arch of the 3"! vertebra, 
the 4 through the posterior margin of the arch of the 3", the 5™. 
similarly through the 4! and so on. The 15t, 2™¢, 3‘ and 4" take part 
