First Type. — Acephali in the form of a rounded mass, without any indication of extre mities. — Examples have been given by G. Vrolik, Bland, and W. Vrolik, all of twins. The rounded mass is covered with the skin ; it contains an intestinal fold, and receives the insertion of the umbilical cord. In general there is found in it the rudimental indication of vertebrx and of spinal medulla.
Second Type. — Acephali in the form of a rounded mass, with indication of feet. — The chief observations of this form have been given by G. Vrolik and Clarke, in cases of twins. They have an umbilical cord, rudi mental external genital parts, and an anal orifice, with an imperfect abdominal cavity, in which are contained an intestinal loop formed by a colon and cmcum, and kidneys. Conse quently all the thoracic viscera, the liver, the spleen, pancreas, stomach, and the small in testines, are wanting ; but there is a rudiment of a nervous system, a tolerably complete right inferior extremity, a pelvis, and a left separate foot, without femur and crus. (Figs. 616, 617.) the observations which we know of it are of twins, and in one case of three children born at one birth. In many it is proved that the mother of the acephalus has been often fecun dated. They are rarely full-grown at birth, and they have in most instances a placenta common to them and the well-formed child, but with a separate cord ; the fcetal membranes also appear to be common to both. The cord of the acephalus contains sometimes two, sometimes three or four vessels (T. II. Kalck). The integuments of the monster, truncated at its upper part, are irregularly tumified, by a large quantity of thick, pale, or yellowish subcutaneous cellular tissue. Interiorly there are lumbar vertebrm, with a pelvis, and the bones and muscles of inferior limbs, besides the spinal marrow and its nerves ; the lumbar and sacral parts of the sympathetic nerve ; blood-vessels without a heart, of which the arteries are connected with the umbilical ar teries, and the veins with the umbilical vein ; a loop of intestines ; uropoietic, and genital parts. All the other parts are wanting.
Fifth Type. —Acephali in which the trunk is much more developed, with an imperfect tho rax, composed of some dorsal vertebree and ribs. The superior limbs are wanting.— The only difference between this and the preceding type is in the more complete trunk, there being a thorax superadded to the abdomen. In all the other points the structure re sembles that of the fourth type ; they are Third Type.—Acephali in which the trunk is more developed, without a head and thoracic or superior extremities, but composed If an in complete trunk, with an imperfect inferior extre mity.— In the lowest grade of this monstrosity may be ranked an acephalus observed by Ruysch, consisting only of a leg. Somewhat more perfect is the acephalous inferior ex tremity of a goat, mentioned by Hayn. It consisted of a pelvic bone, with the other bones of the inferior extremity, some muscles, the vessels and nerves of the femur, which were probably connected with the umbilical cord of the perfect goat born at the same time as the acephalus.
Fourth Type. Acephali in which the trunk is more developed, without a thorax and without superior limbs, and composed of an domen, genital organs, and two inferior limbs.
The hypogastrium and the two inferior limbs are, then, more or less completely formed parts. With exception of one, all always twins, and not full grown. As far as it has been mentioned by different obser vers, there is either a common placenta, with two cords (Ponjol), or with one cord split into two (Mery) ; or there are two placenta connected together (Herholdt); or there are two totally separate ova, with a double placenta (Monro). The external appear ance differs from that of the fourth type, by greater length, and less truncated upper part of the body, in which a feeble indication of head may sometimes be visible (Ponjol, Prochaska). The integuments are as in the fourth type ; the toes are generally mal formed ; the arms and the external genital organs are often abnormal. To the lumbar part of the spinal column is joined an imper fect osseous thorax, sometimes with cervical vertebra (Hevermann), but without thoracic viscera. The diaphragm exists in most cases. There are vessels without a heart, which cohere with the umbilical vessels. The viscera of the epigastric region are commonly want ing ; Atkinson mentions only a liver. In some intestines can be recognised either as intestina tenuia or crassa. The uropoietic organs, and the internal parts of generation are commonly present. There is in all a spinal marrow. The observations as to the nervous system are very incomplete. (Seefigs. 618, 619.) Sixth Type. -- Acephali with a trunk com posed of a thorax and an abdomen, and with two superior and two inferior limbs. — When the trunk is more developed, the thorax becomes more convex, is more distinct from the abdo men, and supports two superior limbs. These acephali, too, are twins, at least in the greater number of the cases. They are often not full-grown, and borne by women who haie frequently been pregnant. The placenta is in general common to the two foetuses, but with two cords. The thorax is more perfect than in the fifth type ; the upper part of the body terminates not in an obtuse end, but in a broad and flat surface, havir g a fissure in the midst, with an indication of a head. The sternum is often rudimentary, and the osseous frame of the superior limbs is very incom plete. To the spinal column are added cervical . and sometimes a confused indication of cranial bones. There is usually a dia phragm, but neither heart nor lungs. There are commonly two vascular trunks, an arte rial and a venous. With the venous is con nected the umbilical vein ; and from the in ternal iliac arteries arise the umbilical arteries. There are uropoietic organs, and an intestinal canal, with a cacal termination ; and some times a liver. This latter is, however, some times wanting, together with the spleen and the pancreas. In the intestinal tube there is no meconiurn, but only a mucous substance. The nervous system is very incomplete; but there is constantly a spinal marrow with the abdominal part of the sympathetic. I have observed distinct muscles, of which the pre sence has been denied by others.