In this article we will discuss about the structure of different vertebrae.
I. Procoelous:
A. Bufo sp. (Toad), Rana sp. (Frog):
1. Hypapophysis and chevron bone absent.
2. Neural spine:
A median elevation (Bufo); backwardly directed (Rana).
3. Atlas:
Prezygapophyses absent.
4. Typical vertebra:
Postzygapophysis present.
B. Calotes sp. (Lizard):
1. Presence of hypapophysis in cervical and chevron bone in caudal.
2. Neural spine:
A crest at right angle to centrum.
3. Atlas:
Bony ring, centrum absent.
4. Axis:
An odontoid process with hypapophysis.
5. Cervical:
Hypapophysis well or ill developed or absent.
6. Thoracolumbar:
Neural spine a crest; no hypapophysis.
7. Sacral:
Transverse processes well developed.
8. Caudal:
Y-shaped chevron bone.
2. No distinct suture between premaxilla and maxilla.
3. Canines do not project beyond other teeth.
4. Nasal bones elevated on the facial plane.
5. Nasal aperture long, oval or pyriform.
6. Dental formula 
II. Amphicoelous:
Fish, Rana sp. (Frog):
A. Fish. Caudal, with haemal spine.
B. Rana sp. Eighth vertebra.
III. Heterocoelous:
Columba sp. (Pigeon):
1. Atlas:
Bony ring, with centrum, without suture,
2. Axis:
Odontoid process present.
3. Cervical:
Vertebrarterial foramen present.
4. Free thoracic:
Presence of hypapophysis and costal facets.
5. Synsacrum:
A compound bone formed by the fusion of posterior thoracic; all the lumbars (5 or 6); 2 sacrals and the anterior caudals (5).
6. Pygostyle:
Plough-shaped, bent upwards and formed by the fusion of last 4 caudals.
IV. Acoelous:
Cavia sp. (Guinea pig):
1. Atlas:
Ring-like, centrum and transverse processes present.
2. Axis:
Odontoid process present.
3. Cervical:
Transverse process stuby and bifid in 4, 5 and 7.
4. Thoracic:
a. Anterior thoracic (1 to 10). Centrum bears capitular facets; transverse processes well built and with facet for tuberculum.
b. Posterior thoracic (11 to 13/14). Centrum bears lateral facets; transverse processes short.
V. Biconvex:
Bufo sp. (Toad), Rana sp. (Frog):
Ninth vertebra.
Identification:
1. Teleost (Bony fish):
Precaudal vertebra:
(Fig. 42.22A)
1. Centrum amphicoelous (concave on both ends).
2. Neural arch dorsal, with a narrow neural spine and a neural canal.
3. Paired pre and postzygapophyses present.
4. Paired transverse processes, with facets for articulation of ribs.
Caudal vertebra:
(Fig. 42.22B)
1. Centrum amphicoelous.
2. Dorsal neural arch with a narrow neural spine and a neural canal.
3. Paired pre and postzygapophyses present.
4. Ventral haemal arch with a narrow haemal spine and a haemal canal.
2. Bufo sp. (Toad); Rana sp. (Frog):
Atlas:
First cervical vertebra (Fig. 42.23)
1. Ring-like.
2. Centrum small and bears two concave facets anteriorly.
3. Neural arch encloses a neural canal.
4. A pair of well developed postzygapophyses present.
5. Transverse processes and prezygapophyses absent.
Typical vertebra:
(Fig. 42.24)
1. Centrum procoelous (concave anteriorly, convex posteriorly).
2. Neural arch encloses a neural canal.
3. Presence of a dorsomedian, depressed, neural spine.
4. A pair of transverse processes present.
5. Pre and postzygapophyses present.
Rana sp. Eighth vertebra:
(Fig. 42.25)
1. Centrum amphicoelous.
(Rest as in a typical vertebra)
Bufo sp. Ninth vertebra:
(Fig. 42.26A)
1. Centrum procoelous.
2. Presence of two round condyles on the posterior face.
3. Transverse processes flat and broad distally.
4. Postzygapophyses absent.
(Rest as in a typical vertebra except points 2 and 3)
Rana sp. Ninth vertebra:
(Fig. 42.26B)
1. Centrum biconvex.
2. Transverse processes cylindrical, stout and backwardly directed.
(Rest as in Bufo)
In frog, the transverse processes are relatively small, outward and downward in the 2nd and 3rd vertebrae; upward and backward in 4th, 5th and 6th.
Bufo sp. Urostyle:
(Fig. 42.27A)
1. Long, slender, rod-like and narrows posteriorly.
2. A mid-dorsal neural crest present.
3. A pair of concavities present on the anterior end.
4. A narrow hole, neural canal runs throughout the urostyle.
Rana sp. Urostyle:
(Fig. 42.27B)
(Point 1 to 3 as in Bufo sp.)
4. Neural canal restricted to anterior part only.
3. Calotes sp. (Garden lizard); Varanus sp. (Monitor):
Atlas:
First cervical vertebra:
(Fig. 42.28)
1. Ring-like.
2. Hypo-centrum (incomplete centrum) occupies ventral position.
3. Neural arch encloses a cavity, which is horizontally divided by a ligament into two, upper neural canal and lower odontoid fossa.
4. Presence of a concave articular facet ventrally, on the anterior face.
5. Presence of a rudimentary hypapophysis (absent in Varanus sp.).
6. A pair of postzygapophyses present.
7. A pair of blunt posterolateral processes present below postzygapophyses.
8. Neural spine, prezygapophyses absent.
Axis:
Second cervical vertebra:
(Fig. 42.29)
1. Centrum procoelous.
2. Odontoid process (centrum of first vertebra) present.
3. Neural arch encloses a neural canal.
4. Neural spine crest-like and directed posteriorly (almost vertical and more wide anteroposteriorly in Varanus sp.).
5. Pre and postzygapophyses well developed.
6. Presence of a vertical hypapophysis.
7. Rudiments of diapophyses in the form of anterolateral tuberosities.
8. Odontoid process bears hypapophysis in the form of a spine (Varanus).
Typical cervical vertebra:
(Fig. 42.30)
1. Centrum procoelous, well developed.
2. Neural arch encloses a neural canal.
3. Neural spine crest-like and directed posteriorly (almost vertical in Varanus sp.).
4. Pre and postzygapophyses present.
5. Two capitular facets present anteriorly.
6. Presence of a ventral hypapophysis.
Thoracolumbar vertebra:
(Fig. 42.31)
1. Centrum procoelous, well developed.
2. Neural arch encloses a neural canal.
3. Neural spine crest-shaped.
4. Pre and postzygapophyses present.
5. Two capitular facets present anteriorly.
6. Hypapophysis absent.
Sacral vertebra:
(Fig. 42.32)
1. Centrum procoelous, well developed.
2. Neural arch encloses a neural canal.
3. Neural spine crest-shaped.
4. Pre and postzygapophyses present.
5. Presence of two transverse processes.
6. Capitular facets absent.
7. Hypapophysis absent.
Caudal vertebra:
(Fig. 42.33)
1. Centrum procoelous, well developed.
2. Neural arch encloses a neural canal.
3. Neural spine crest-shaped.
4. Pre and postzygapophyses present.
5. Presence of two transverse processes.
6. A ventral Y-shaped chevron bone encloses a haemal canal.
7. Capitular facets absent.
8. Hypapophysis absent.
The caudal vertebrae gradually become smaller posteriorly and are tubular further behind. The above structures are identified up to 13 or 14 caudal vertebra.
4. Snake:
Precaudal vertebra:
(Fig. 42.34A)
1. Centrum procoelous, well developed.
2. Neural arch encloses a neural canal.
3. Neural spine crest-like.
4. Transverse processes small.
5. Pre and postzygapophyses present.
6. Presence of additional articulating surfaces, zygosphene at the anterior and zygantra at the posterior face.
7. Presence of capitular facets.
Caudal vertebra:
(Fig. 42.34B)
1. Transverse process rod-shaped and well developed.
2. Capitular facets absent.
(Rest as in precaudal vertebra; points 1, 2, 3, 5, 6)
Chevron bone or haemal arch present.
5. Columba sp. (Pigeon); Callus sp. (Fowl) Atlas:
(Fig. 42.35)
1. Small, ring-like, bones completely fused and without any suture.
2. A distinct centrum lacking.
3. Odontoid fossa, a notch, present at the posterior side of the thickened ventral portion.
4. A cup-shaped facet for articulation with occipital condyle present anteriorly,
5. Postzygapophyses present.
6. Prezygapophyses absent.
Axis:
(Fig. 42.36)
1. Centrum heterocoelous, i.e., surface saddle-shaped, anterior face concave from side to side and convex from above downwards; posterior face convex from side to side and concave from above downwards.
2. Odontoid process (centrum of first vertebra) peg-like.
3. Neural arch encloses a neural canal.
4. Neural spine blunt.
5. Pre and postzygapophyses well developed.
6. Hypapophysis small and flattened.
Typical cervical vertebra:
(Fig. 42.37)
1. Centrum heterocoelous.
2. Neural arch encloses a neural canal.
3. Neural spine crest-shaped (short in anterior vertebrae; longer in posterior ones).
4. Pre and postzygapophyses present.
5. Transverse processes present.
6. Vestigeal, double-headed ribs fused with the vertebra and directed posteriorly.
7. Vertebrarterial foramen present.
8. Articulating surfaces of the centrum contain synovial capsules, meniscus and supplementary ligament.
N.B. Posterior cervicals bear hypapophysis.
Free thoracic vertebra:
(Fig. 42.38)
1. Centrum heterocoelous.
2. Neural arch encloses a neural canal.
3. Neural spine large and crest-shaped.
4. Pre and postzygapophyses present.
5. Transverse processes present.
6. Presence of capitular facets on centrum and tubercular facets on transverse processes for articulation with double-headed ribs.
7. Vertebrarterial foramen present.
8. Articulating surfaces of the centrum contain synovial capsules, meniscus and supplementary ligament.
9. Presence of hypapophysis.
Synsacrum:
(Fig. 42.39)
1. Elongated, more or less triangular in shape.
2. Formed by the fusion of 13 to 14 vertebrae in Columba and 15 in Gallus.
3. The vertebrae are posterior thoracic 1, lumbar 5 to 6, sacral 2, anterior caudal 5 in Columba sp. and posterior thoracic 1, lumber 7, sacral 2 and anterior caudal 5 in Callus sp.
Free caudal vertebra:
(Fig. 41.40)
1. Centrum short but prominent and appears as acoelous (flat on both the faces).
2. Neural arch quadrangular and encloses a narrow neural canal.
3. Neural spine moderately developed and bifid.
Pygostyle or ploughshare bone:
(Fig. 42.41)
1. A laterally compressed skeletal structure, upturned posteriorly.
2. Formed by the fusion of last four caudals.
3. Centrum heterocoelous but appears as
4. Facet at the anterior end for articulation with last free caudal vertebra.
6. Cavia sp. (Guinea pig); Oryctolagus sp. (Rabbit):
Atlas:
(Fig. 42.42)
1. Ring-like, centrum very small.
2. Neural arch encloses a cavity, which is divided by a ligament into two, upper neural canal and lower odontoid fossa.
3. Neural spine small.
4. Presence of two concave articular facets on both the anterior and posterior faces.
5. Transverse processes small and flat (well developed in rabbit).
6. Presence of vertebrarterial foramen at the base of the transverse process and alar foramen dorsolaterally.
Axis:
(Fig. 42.43)
1. Centrum acoelous (flat on both faces) and broad.
2. Odontoid process, (centrum of first vertebra) peg-like.
3. Neural arch with upper lamina and lower notched pedicel, and encloses a neural canal.
4. Neural spine compressed and directed anteroposteriorly.
5. Transverse processes small, backwardly directed and bear vertebrarterial foramen at the base.
6. Postzygapophyses present, prezygapophyses absent.
Typical cervical vertebra:
(Fig. 42.44)
1. Centrum acoelous, short but broad from side to side.
2. Neural arch with upper lamina and lower notched pedicel, and encloses a neural canal.
3. Neural spine small.
4. Transverse processes stuby and bifid in C4, C5, C7 with three terminal lobes in C6 in Cavia sp.
a. Stuby and bifid except C7 in Oryctolagus sp.
5. Presence of intra-vertebral foramen.
6. Pre and postzygapophyses well developed.
Anterior thoracic vertebra:
(Fig. 42.45)
1. Centrum acoelous, compact and small.
2. Neural arch notched in front and behind and encloses a neural canal.
3. Neural spine long, narrow and directed backward.
4. Transverse processes short, stout and strongly built.
5. Presence of concave capitular facets on the sides of the centrum and tubercular facets on the ventral surface of the transverse processes for articulation with capitulum and tuberculum of ribs.
6. Pre and postzygapophyses present.
Posterior thoracic vertebra:
(Fig. 42.46)
1. Centrum acoelous, compact and small.
2. Neural arch notched in front and behind and encloses a neural canal.
3. Neural spine small.
4. Transverse processes small and lack articular facets for ribs.
5. Pre and postzygapophyses present.
Lumbar vertebra:
(Fig. 42.47)
1. Vertebra large with acoelous centrum.
2. Neural arch encloses a neural canal.
3. Neural spine flat and directed anteriorly.
4. Transverse processes large, expanded, directed forward and downward.
5. Pre and postzygapophyses well developed.
6. A pair of metopophyses, dorsal to the prezygapophyses, a pair anapophyses, below the post zygapophyses and a ventromedian ridge, hypapophysis present.
Sacral vertebra (Sacrum):
(Fig. 42.48)
1. Three to four small vertebrae fused to form sacrum.
2. The sizes of the vertebrae decreases posteriorly.
3. Centrum acoelous.
4. Neural arch encloses a neural canal.
5. Neural spine well developed and vertical.
6. Transverse processes present, those of the first sacral vertebra flat and laterally expanded.
7. Pre and postzygapophyses small.
8. Metapophyses dorsal to prezygapophyses, paired and small in size.
9. Anapophysis and hypapophysis absent.
10. Presence of intra-vertebral foramina.
Caudal vertebra:
(Fig. 42.49)
1. Size of the vertebrae decreases posteriorly and the last two are rod-like.
2. Centrum acoelous.
3. Neural spine directed upward.
4. Transverse processes absent.
5. Pre and postzygapophyses very small.