MR. ST. GEORGE MIVART ON THE VERTEBRATE SKELETON. 391 
DESCRIPTION OF THE PLATE. 
PLATE LIII. 
Fig. 1. Ideal generalized expression of the vertebrate skeleton. Descending from the cranium (or ex- 
panded, anterior part of the epaxial system) are the enlarged anterior parts of the hypaxial 
system :—1, the trabeculz cranii; 2, the mandible; 3, the hyoidean arch; 4, the first branchial 
arch. The paraxial parts are made to show their generally double origin (tubercular and capi- 
tular), and a certain tendency to distal bifurcation. "These parts diminish in the caudal region 
concomitantly with the increase in the hypaxial system. The skull, or expanded anterior end 
of the epaxial system, is represented as consisting of three segments (I., II., TIL), with a sense- 
capsule (nasal, ocular, auditory) at the anterior aspect of each segment. "The limbs are sup- 
posed to be simplified according to the view before expressed by me in the Transactions of 
the Linnean Society—namely, a correspondence between the greater tuberosity and the lesser 
trochanter, and between the lesser tuberosity and the great trochanter. 
Fig. 2. Diagram of a transverse section of the most developed skeletal segment according to the ideal 
here expressed. From above the centrum the epaxial parts, E (neural arches and neural spine), 
ascend. From each side of the centrum the paraxial system proceeds outwards and downwards 
to coalesce in the sternum below. 
i, tubercular process; tr, tubercular part of the rib; tr, its continuation outwards towards the sur- 
face of the body; c, capitular process; cr, capitular part of the rib; vr, vertebral rib; sr, 
sternal rib; s, sternum. From beneath the centrum the hypaxial system descends. 
A, The part of the hypaxial system which is related to the great vessels; B, part related to the 
alimentary system ; C, part related to the heart. 
Fig. 3. Diagram of the conditions existing in sharks. N, neural canal; B, alimentary tract, surrounded 
by solid hypaxial parts, H (the branchial arches). V, the aortic vessels, extending up outside 
the branchial arches and inside the paraxial system (P), here represented by certain external 
branchial cartilages. 
Fig. 4. Diagram of the conditions existing in the Lamprey. N, neural canal; B, alimentary tract, only 
bounded by H, a membranous representation of the hypaxial system. V, the ascending vessels ; 
P, the paraxial system or branchial basket. 
Fig. 5. Branchial arches, H, of the Monk fish (Squatina), attached to the under surface of the spine ; P, 
ridge representing the root of the paraxial system. Drawn, by permission, from the specimen 
No. 442 in the Museum of the Royal College of Surgeons. 
Fig. 6. Part of the vertebral column of a Flounder, showing the caudal arches, HP, apparently formed 
by the bending down of the paraxial parts of the trunk. 
Fig. 7. Part of the vertebral column of a Sole, showing the caudal arches formed by the simple elongation 
of the hypaxial elements of the trunk—the paraxial elements, P, retaining their independence 
till they disappear. 
Fig. 8. Under surface of part of the vertebral column of Lophius, showing the caudal arches, H, formed 
by the production of the margins of the subcentral aortic groove of the trunk. 
Fig. 9. Vertebra of Naseus fronticornis (copied from Dr. Cleland's article in the Natural-History Review, 
vol. iii. p. 129). H, hypaxial elements; P, paraxial elements, consisting of :—ż, tubercular pro- 
cess; tr, the rib from it, continuing outward toward the body-wall; c, capitular process, which 
is continued on by membrane only. 
Fig. 10. Part of the vertebral column of a fish, showing the suspension of hypaxial elements, H, to the 
paraxial parts, P, of the first caudal vertebrze. 
