Nuchal layer

The lamina of the nuchal ligament (Lamina nuchae), or nuchal layer is a broad median divider extended from the cord, with which the dorsal border is continuous, to the cervical spinous processes on which it connects through strips. As the cord, it is fibrous in Men, but elastic in domestic Mammals.

In Carnivorous, is is so weak that it is usually considered missing; it is also nearly absent in Pigs.

At the opposite, it is thick and very extended in great Ungulates. In Equidae and Ruminants, it is made of two yellow elastic laminas, easy to dissociate, spread on each side of an intermediate lamina, less rich in elastic  fibers; this one is hardly represented in Equidae but very developed in Bulls, where the two other laminas are less extended, only inserted on the three vertebrae following the atlas.

In these great species, the nuchal layer, also attached to the first thoracic spinous processes, delimits just in front of these an 'oval foramen', particularly remarkable in Equidae. Besides, it it does not attach to the cranial extremity of the cord and is lacking at the level of the atlas. 

In Equidae, the insertions of the nuchal layer vary. Its lamellae attach mainly from C2 to C5 in the modern horse and from C2 to C7 in the primitive horse.