Hemivertebrae in dogs are most common in the tail, resulting in a screw shape. Block vertebrae
Block vertebrae occur when there is improper segmentation of the vertebrae, leading to parts of or the entire vertebrae being fused. The adjacent vertebrae fuse through their intervertebral discs and also through other intervertebral joints so that it can lead to blocking or stretching of the exiting nerve roots from that segment. It may lead to certain neurological problems depending on the severity of the block. It can increase stress on the inferior and the superior intervertebral joints. It can lead to an abnormal angle in the spine, there are certain syndromes associated with block vertebrae; for example, Klippel–Feil syndrome. The sacrum is a normal block vertebra. Fossil record
Evidence for block vertebrae found in the fossil record is studied by paleopathologists, specialists in ancient disease and injury. A block vertebra has been documented in T. rex. This suggests that the basic development pattern of vertebrae goes at least as far back as the most recent common ancestor of archosaurs and mammals. The tyrannosaurs block vertebra was probably caused by a "failure of the resegmentation of the sclerotomes". Butterfly vertebrae
Butterfly vertebrae have a sagittal cleft through the body of the vertebrae and a funnel shape at the ends. This gives the appearance of a butterfly on an x-ray. It is caused by persistence of the notochord (which usually only remains as the center of the intervertebral disc) during vertebrae formation. There are usually no symptoms.
Pancuronium (trademarked as Pavulon) is an aminosteroid muscle relaxant with various medical uses. It is used in euthanasia and is used in some states as the second of three drugs administered during lethal injections in the United States. Mechanism of action
Pancuronium is a typical non-depolarizing curare-mimetic muscle relaxant. It competitively inhibits the nicotinic acetylcholine receptor at the neuromuscular junction by blocking the binding of acetylcholine. It has slight vagolytic activity, causing an increase in heart rate,  but no ganglioplegic (i.e., blocking ganglions) activity. It is a very potent muscle relaxant drug, with an ED95 (i.e., the dose that causes 95% depression of muscle twitch response) of only 60 µg/kg body weight. Onset of action is relatively slow compared to other similar drugs, in part due to its low dose: an intubating dose takes 3–6 minutes for full effect. Clinical effects (muscle activity lower than 25% of physiological) last for about 100 minutes. The time needed for full (over 90% muscle activity) recovery after single administration is about 120–180 minutes in healthy adults. The effects of pancuronium can be at least partially reversed by anticholinesterasics, such as neostigmine, pyridostigmine, and edrophonium. Development
Workers at Organon were inspired by the structure of the aminosteroid alkaloid malouetine to develop a series of aminosteroid neuromuscular blockers based on an androstane nucleus, culminating in the development of pancuronium bromide.Pancuronium is designed to mimic the action of two molecules of acetylcholine with the quaternary nitrogen atoms spaced rigidly apart by the steroid rings at a distance of ten atoms (interonium distance).