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PHYLOGENETIC
SIGNIFICANCE IN ZEBU CATTLE [Vol.. XXV, Part IV,
In the flesh-humped sanga cattle the spinous processes of the anterior dorsal
vertebrae display considerable variability. In some the fissure is moderately deep,
although commonly not quite so deep as in the zebu cattle ; in others it is hardly
perceptible. Even within one and the same breed the differences are considerable.
The variability of this feature among flesh-humped sanga cattle is due to their
derivation from a mixture of flesh-humped zebu characterised by bifid spinous
processes—and straight-backed longhorn cattle in which spina bifida does not occur.
In fat-humped sanga cattle the neural spines of the dorsal vertebrae are nearly
always typically zebu as may be expected in a cross commonly consisting of two
different zebu strains excepting one of longhorn. The neural spines are distinctly
bifid, long and slender, markedly compressed antero-posteriorly, and curving well
backwards.
Several authors who have commented on the origin of the zebu cattle attribute
considerable importance to the peculiar bifurcation of the spinous processes of the
anterior dorsal vertebrae. Pettit [1909] and Gans [1915] regard the bifidity of the
spinous processes as a typical racial character of the zebu cattle ; Klatt [1927]
goes even further, expressing the hope that it may yet provide an important clue
in the quest of the zebu's wild ancestors.
However, this view cannot be upheld since a number of humped cattle seem
to be entirely devoid of bifid neural spines. Spina bifida, for instance, is absent
not only in flesh-humped brachyceros cattle of Egypt and western Asia and in
many flesh-humped sanga cattle of Africa, but also in the pituitary dwarf zebu
skeleton from India in the Museum of the Royal College of Surgeons, London,
which the author examined in 1936. On the other hand, Duerst [1931] mentions
the occasional occurrence of bifid spinous processes in straight-backed cattle (Sim-
mentaler), where it is ascribed to the strong pull exercised by the weight of the head
on the splenius and the nuchal and supraspinous ligaments. Further, no wild
bovine seems to have the neural spines of the dorsal vertebrae bifid, this character
occurring only in domesticated cattle.
Spina bifida is found in numerous animals in different parts of the spine : In the
elephant, giraffe, camel, llama, Macrauchenia, Orycteropus and Hydrochoerus the
Processus spinosus of the epistropheus is bifid, in Myrmecophaga didactylus trifid.
In Cervus axis the neural spines of the 4th to 7th cervical vertebrae are bifurcated
while in Trichechus those of the 5th and 6th cervical vertebrae and in Crocuta cro-
cuta the Processus spinosus of the 7th cervical vertebrae are bifurcated. In Ornitho-
rhynchus and Dasypus duadecimcinctus several thoracic vertebra, and in the seals
a number of lumbar vertebra, have bifid neural spines. In Rhinoceros tichorhinus
the 2nd sacral vertebrae is distinguished by the bifidity of the neural spinous process,
while in the Bovidae, rats and mice the spinous processes of the caudal vertebra
are bifid [Mijsberg, 1926].
In the rabbit, spina bifida occurs as an abnormality. The degree to which it
is developed varies greatly, although the hereditary basis is the same. Hammond
[1940] attributes this to a mutation caused by a defective gene. The probable
explanation of these variations in the appearance of the character is held to be the
variation in the stage of development of the embryo at which the defective gene