In Uromastrix 'Y' shaped chevron bone is found in which vertebra?

Option 4 : Atlas

Concept-

• Uromastyx is a genus of lizards native to Africa and the Middle East.
• Most species in the genus prefer living in rocky or hilly areas with plenty of underground hiding places.
• Many people commonly refer to these lizards as spiny-tailed lizards, uromastyces, dab lizards, or mastigures.

Caudal vertebrae of Uromastyx-

• Y-shaped chevron bone attached to the ventral surface of the centrum, is the characteristic feature of the vertebra of reptiles. 
• The caudal vertebrae progressively become smaller towards the posterior end, finally getting reduced to mere bony rod-like centrum.
• Anterior caudal vertebrae:
  • In the anterior caudal vertebrae the centrum is longer and strongly procoelous.
  • The neural spine is long, pointed and directed backwards.
  • Pre- and post-zygapophyses are well developed.
  • Transverse processes are long, slender, and directed outwardly and downwardly.
  • Y-shaped chevron bone has two haemal arches attached to the ventral surface of centrum and a long downwardly directed haemal spine.
• Posterior caudal vertebrae:
  • It resembles the anterior caudal vertebrae with the exception of absence of chevron bone.
  • The various processes get gradually reduced.​

Sacral vertebrae-

• Both the sacral vertebrae are firmly united.
• These are stout and strong giving support to the pelvic girdle.
• Anterior or first sacral vertebra is more stout than the second.
• Its centrum is short and strongly procoelous.
• The neural spine is small crest-like.
• Pre- and post-zygapophyses are well developed and hypapophysis is absent.

Thoracic vertebrae-

• Thoraco-lumbar vertebrae occur in the thoracic and abdominal regions.
• Thoraco-lumbar vertebrae are similar to cervical vertebrae but they are slightly larger in size and lack hypapophysis.
• Centrum is procoelous and neural spine is vertical crest-like.
• Pre- and post-zygapophyses are present.

Atlas vertebrae-

• Atlas vertebra is the first vertebra of cervical region.
• It is small and ring ­like in shape with no distinct centrum.
• It is composed of three distinct bony pieces of which two are dorso-lateral and one ventral around the neural canal.
• The neural canal is divided by a ligament into the dorsal and ventral portion which is downwardly projected into a small spine.
• Ventral piece occupies the position of centrum.