318 
DE. CLELAND ON THE EELATIONS 
the quadrate jugal, but the bone called mastoid by Professor Owen, corresponds to the 
mammalian squamous. The quadrate bone of the bird has been abundantly proved to 
correspond to the incus of the mammal. The elements of the limb-arch are the incus, 
malleus, and lower jaw ; and its superior member, the incus, is, throughout the vertebrate 
series, connected with the mastoid and squamous bones. As for the stapes, it is a radia- 
tion of the petrous sclerotome, and corresponds to the structure which supports the eye 
of the Shark, and to the ethmoidal turbinations in the presphenoidal and ethmovomerine 
sclerotomes. While, on the one hand, the rib-arches belong to the individual segments 
of the body, on the other there are three limb-arches, corresponding to the three great 
regions of the body : one for the head — the region in which the highest development of 
organs of animal life takes place ; one for the cervical region — the region in which is 
the highest development of the vascular organs ; and one for the abdomen — the region 
in which the greatest development is found of organs of vegetable life. 
Explanation op the Plates. 
PLATES IV. & V. 
Fig. 1. Bones from specimen referred to in the text as No. 1. 
A. The vomer, ethmoid, sphenoidal spongy bones, and left palate and maxil- 
lary bones, from the skull of an infant, slightly enlarged, and viewed from 
behind : — a, orbital plate of the ethmoid ; 5, posterior extremity of the vomer ; 
c, sphenoidal process of the palate-bone ; d, orbital surface of the palate-bone, 
and, immediately above it, the orbital portion of the sphenoidal spongy bone : 
between the two processes of the palate-bone is the spheno-palatine foramen, 
completed above by the inferior portion of the sphenoidal spongy bone: 
e, the superior portion of the sphenoidal spongy bone ; f, inferior portion. 
B. Another view taken from the same specimen : — a, b, c, the parts of the infe- 
rior margin of the vomer which articulate with the palate, maxillary, and 
intermaxillary bones respectively ; d, inferior aspect of the sphenoidal spongy 
bone ; e, orbital plate of the ethmoid, seen in perspective ; f, inferior tmhi- 
nated process of the ethmoid. 
Fig. 2. Bones from specimen referred to in the text as No. 2. 
A. Ethmoid, with sphenoidal spongy bones attached : — a, cribriform plate ; 
b, os planum; c, superior portions of the sphenoidal spongy bones, with 
space between them for the body of the presphenoid ; e, e, orbital portions ; 
f, /, inferior portions. 
B. Sphenoid : — a, body of postsphenoid ; b, body of presphenoid. 
Fig. 3. Bones from specimen referred to in the text as No. 3. 
A : — a, part of the orbital 'plate of the frontal ; b, os planum ; c, presphenoid ; 
