Pseudencephalic foetuses have been divided into two classes, according as there exists a vertebral fissure or not; nosencephalic, where the vascu lar tumor occupies only the upper part of the head; thlipsencephalic, where the anomaly is much more accentuated. The tumor projects so much backwards as to sometimes invade the first cervical vertebra:. It is a frequent monstrosity in the human race, but unknown iu animals.
Pseudencephalic foetuses, properly so-called, may be considered as thlip sencephalic with the vertebral column largely open even down to the lumbar region. Tho disjointed vertebral bodies are widely separated, the spinal marrow has disappeared, and may not have been replaced by a vascular tumor. The skin of the back along the fissure is lacking, and the eater .
nal covering is represented by the meniugeal membranes.
Anencephalic Fceluses.—These may be considered as pseudencepha lie without the fungous tumor. Other anomalies in development are fre quently present. This variety is found almost exclusively in the human species, and usually in the female. According to Meckel, Saint-Hilaire and Dareste, the anomaly is the result of an arrest of development, due to external pressure on the amnion. It may be subdivided into: Deren cephalic foetuses, where the vault of the skull is largely open, all the bones having been pushed laterally, in a rudimentary state (Fig. 198); the occi pital foramen is not recognizable. The upper cervical vertebra:, are in cluded in the arrest of development, as also, at times, the first dorsal.
Throughout the fissure the nervous centres are completely lacking. This is a comparatively rare monstrosity.
Anencephalio (true) Fcetus.—Where the arrest in development extends throughout the entire vertebral canal, which is open and transformed into a groove without special depth. The spinal marrow is lacking. Anon cephalic foetuses are distinguished from derencephalic in that the fissure of the vertebral column is much more extensive.
Such foetuses are often remarkable on account of their development.
The liquor amnii is often profuse. The head is small, immediately on top of the trunk, the ears at the level of the shoulders, the face turned wards, the eyes projecting, the tongue often hanging from the mouth.
(Fig. 200.) The chief diagnostic point before birth is the fact, to which Cazeaux calls attention, that, whenever the finger touches the presenting part, the foetus moves convulsively. These movements are probably due
to direct excitation of the brain.
" Version is indicated. ]fit is not possible, the head is pulled down, by a finger or hook in the mouth." (Charpentier.) Cyclocephalic fcetuses present the following character istics: " Absence of nasal apparatus which is more or less atrophied; the visual apparatus of one or the other side badly-shaped, at times rudimen tary, approaches the median line, one eye almost always being confounded with the other." (Saint-Hilaire.) In the lower grades of these monstrosities, the maxillary region is always much deformed, but the inferior portions of the face are not much altered, and the ears are in their normal site. Cyclocephalicism is often complicated by other anomalies, in the limbs or trunk. The fcetuses are usually female, and are usually born before term. When they are born alive, they soon die, which is the result rather of the difficulty of feeding them than of anomalies in the nervous system. According to Dareste, cyclocephalicism is due to an arrest of development of the anterior cere bral vesicle.
Saint-Hilaire makes a division into five varieties: Ethnocephalic.—Where the nasal apparatus is not completely atrophied, but is present in a rudimentary state, with two imperfect nostrils, single one. There are two orbital cavities and eyes.
Cebocephalic.—Where the nasal apparatus is completely atrophied, but two orbits and eyes are present. They resemble monkeys, whence the name.
Rhinocephalic.—Where the nose has only partially disappeared, the two orbits are fused into one, which occupies the median line. (Figs. 201, 202, 203.) The nose has usually one opening. In the orbit two united distinct eyes may often be seen, although every variety may prevail, from double cornea pupil and lens, down to one large eye, oval, large lens with wide transverse diameter.
Cyclocephalic (true).—Where the atrophy of the nasal apparatus is more pronounced than in the rhinocephalic foetus, the nose disappears entirely, and the monster becomes cyclocephalic. (Fig. 204.) the inferior portion of the face is very abnormal. The maxillary bones are lacking, and often the integument projects to such an extent as to look like an elephant's trunk.