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A vertebral rudiment in front of the atlas in some reptiles.

r forming, the front of the head. Procephalic lobe (Zoöl.), that part of the head of an invertebrate animal which is in front of the mouth.

(a) The projecting angle of the ventral side of the sacrum where it joins the last lumbar vertebra.

Having a caudal fin extending around the end of the vertebral column, like that which is first formed in the embryo of fishes; diphycercal.

Pseudhæmal fluid, the circulatory fluid, or blood, of annelids, analogous to the blood of vertebrates. It is often red, but is sometimes green or colorless. -- Pseudhæmal vessels, the blood vessels of annelids.

Any contractile vessel of invertebrates which is not of the nature of a real heart, especially one of those pertaining to the excretory system.

esponds to the inner plate of the pterygoid process of the human skull, but which, in all vertebrates below mammals, is not connected with the posterior nares, but serves to connect the palatine bones with the point of suspension of the lower jaw. -- Pterygoid process (Anat.), a process projecting downward from either…

The plate of bone which forms the posterior end of the vertebral column in most birds; the plowshare bone; the vomer. It is formed by the union of a number of the last caudal vertebræ, and supports the uropigium.

A posterior division of the stomach in some invertebrates.

ey. Quadrate bone (Anat.), a bone between the base of the lower jaw and the skull in most vertebrates below the mammals. In reptiles and birds it articulates the lower jaw with the skull; in mammals it is represented by the malleus or incus.

Of or pertaining to the rachis; spinal; vertebral. Same as Rhachidian.

The spine; the vertebral column.

An extensive artificial group of invertebrates, having all the parts arranged radially around the vertical axis of the body, and the various organs repeated symmetrically in each ray or spheromere.

A class of air-breathing oviparous vertebrates, usually covered with scales or bony plates. The heart generally has two auricles and one ventricle. The development of the young is the same as that of birds.

That part of the eye of an invertebrate which corresponds in function with the retina of a vertebrate.

ur united cells which occupy the axial part of the ocelli, or ommatidia, of the eyes of invertebrates, and contain the terminal nerve fibrillæ. See Illust. under Ommatidium.

One of the group of pigmented cells which surround the retinophoræ of invertebrates. See Illust. under Ommatidium.

One of the curved bones attached to the vertebral column and supporting the lateral walls of the thorax.

That part of the vertebral column which is directly connected with, or forms a part of, the pelvis.

A comprehensive group of vertebrates, comprising the reptiles and birds.