282 REPORT—1846. 
canal. The diverging appendage, sometimes single and anchylosed to the 
arch (lepidosiren); sometimes single and detached like a long, narrow bone 
(some murenoids); more commonly consists of two bones (23, 24), which 
extend outwards, downwards, and backwards from the pleurapophysis (20) ; 
but the more constant and better ossified bone of the two, no. 24, articulates 
posteriorly with the succeeding pleurapophysis (23) and combines its move- 
ments with those of its own arch, just as the diverging appendages of one 
thoracic hemal arch in the bird associate the movements of that arch with 
those of the next in succession (as in fig. 15, pl, a, pl). The hemapophyses 
here, as at the opposite end of the body, begin so far to dissociate themselves 
from the pleurapophyses as to articulate also directly with the centrum (13) 
as well as with the pleurapophyses. I regard this as a very interesting ap- 
proximation to that condition of the typical vertebra which is illustrated by 
the diagram (fig. 14), and which is seen in nature in the caudal vertebre of 
the crocodiles, enaliosaurs and menopome (fig. 28, H). 
From the foregoing analysis it appears, then, that in osseous fishes the 
endoskeletal bones of the head are arranged, like those of the trunk, in seg- 
ments; that these are four in number, and that they closely conform to the 
. character of the typical vertebra. , 
Thus we have four centrums and neural arches : viz. 
N 1. Epencephalic arch (figs. 1 and 5, 1, 2, 3, 4); 
N 1. Mesencephalic arch (figs. 2 and 5, 5, 6, 7,8); 
N 1. Prosencephalie arch (figs. 3 and 5, 9; 10, 11, 12); 
N iv. Rhinencephalic arch (figs. 4 and 5, 13, 14, 15). 
As a collective name for the sum of these immoveably articulated arches 
would be as convenient as the anatomist finds the names ‘sacrum’ and ‘cara- 
pace,’ applied to similarly consolidated portions of vertebral segments in the 
pelvic and abdominal regions of certain air-breathing vertebrates, that of 
‘cranium’ may well be retained for the neural arches of the skull: but it 
should be understood to signify, in all animals, the bones 1 to 15 inclusive ; 
whereas it has, hitherto, been applied variably in different species; some- 
times including sense-capsules and facial bones, intercalated to expand the 
walls.of the cavity for a large brain; and more frequently excluding true 
cranial bones, those of the rhinencephalic arch, for example, which encompass 
as essential a part of the encepbalic chamber, as the sacral vertebre do of the 
neural canal at the opposite end of the vertebral axis ; although in both in- 
stances the extremities of the neural axis may have been withdrawn, in the 
course of its concentrative change and movement, from their original seat. 
The hemal arches indicated by the arrows in fig. 5, the heads marking 
the point of junction or crown, are,— 
H 1. Scapular arch (50-52) ; 
H 11. Hyoidean arch (3s—a3) ;. 
H ur. Mandibular arch (28-32) ; 
H tv. Maxillary arch (20-22). 
The diverging appendages of the hemal arches are,— 
1. The Pectoral (54-57) ; 
2. The Branchiostegal (44) ; 
8. The Opercular (34-37) ; 
4. The Pterygoid (23-24). 
The bones or parts of the splanchno-skeleton which are intercalated with 
or attached to the arches of the true vertebral segments, are,— 
The Petrosal (16) or ear-capsule, with the otolites, 16"; 
The Sclerotal (17) or eye-capsule ; 
The Turbinal (19) or nose-capsule ; 
The Branchial arches ; 
